JP4875037B2 - Magnetic memory, reproducing method thereof, and writing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic memory in which multi-value recording can be achieved and which exhibits favorable thermal stability. <P>SOLUTION: The magnetic memory includes a memory cell 1 having a first ferromagnetic layer 2, a first nonmagnetic layer 4 formed on the first ferromagnetic layer, a second ferromagnetic layer 6 formed on the first nonmagnetic layer, a second nonmagnetic layer 8 formed on the second ferromagnetic layer, and a third ferromagnetic layer 10 formed on the second nonmagnetic layer. The first and third ferromagnetic layers have approximately vertical axes of easy magnetization on film surfaces, respectively. The second ferromagnetic layer has a smaller coercive force than those of the first and third ferromagnetic layers, and the axis of easy magnetization inclines at larger than 0&deg; and 90&deg;or smaller with respect to a vertical direction to the film surface. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a multilevel magnetic memory, a reproducing method thereof, and a writing method.

  In recent years, research and development of spin electronics devices using the spin degree of freedom of electrons has been actively conducted. For example, in a hard disk drive, the magnetization state of a recording medium is controlled by a magnetic field from a magnetic head, and in a magnetic random access memory, the magnetization state of a magnetoresistive element is controlled by a combined magnetic field from two write lines. The method of controlling the magnetization state by such a magnetic field has an old history and is now an established technology.

  On the other hand, with recent advances in nanotechnology, the recording units of the recording medium and the magnetoresistive effect element have been miniaturized, and it has become necessary to control these magnetization states locally on the nanoscale.

  However, since the magnetic field has the property of spreading in space, it is difficult to localize. For this reason, a problem of so-called “crosstalk” that causes erroneous writing due to the influence of the magnetic field on the recording unit and the magnetoresistive effect element other than the write target occurs. If the magnetic field generation source is made small in order to localize the magnetic field, a magnetic field having a magnitude necessary for magnetization reversal cannot be obtained.

  Therefore, “current direct drive type magnetization reversal method” capable of reversal of magnetization without causing “crosstalk” has attracted attention (for example, see Non-Patent Document 1). This is a technique in which a spin injection current as a write current is passed through a magnetoresistive effect element, and magnetization reversal is executed using spin-polarized electrons generated in the magnetoresistive effect element. Specifically, the angular momentum of the spin-polarized electrons is transmitted to the electrons in the magnetic layer serving as the magnetic recording layer in the magnetoresistive effect element, thereby reversing the magnetization of the magnetic recording layer.

  If such a direct current drive magnetization reversal technology (spin injection magnetization reversal technology) is used, the magnetization state can be easily controlled locally at the nanoscale, and the value of the spin injection current can be reduced according to miniaturization. This will help to realize spin electronics devices such as high recording density hard disks and magnetic random access memories.

  In this spin injection magnetization reversal technique, as a method of reducing the current density, a magnetic layer sandwiched between magnetic layers (pinned layers) having magnetizations fixed in opposite directions with nonmagnetic layers above and below the magnetic reference layer. Recording elements have been proposed. Furthermore, in order to obtain a structure in which the magnetization directions of the pin layers in opposite directions are arranged in the direction perpendicular to the film surface, and an upper and lower pinned layer in which the magnetization directions are opposite to each other, a film with a changed coercive force can be used. Connection with an antiferromagnetic film is disclosed.

However, there are problems with this technology. That is, the current density Jc of the spin injection current required for the magnetization reversal becomes a large value of 1 × 10 ⁷ A / cm ² or more. When such a large value is reached, reliability problems such as deterioration of element characteristics occur due to the influence of heat generated in the magnetoresistive element.

  As countermeasures, for example, several proposals have been made such as reducing the value of the saturation magnetization Ms of the magnetic material constituting the magnetoresistive element (see, for example, Patent Documents 1 and 2). However, when the saturation magnetization Ms is reduced, there is a problem that the thermal fluctuation resistance of the magnetization state of the free layer under the bias magnetic field from the pinned layer is deteriorated. As can be seen from the same analogy with the problem of high density in in-plane recording, when the magnetization of the pinned layer and the magnetization of the free layer are in the same direction, the free layer is in the direction of assisting its own magnetization. It is stable because it receives a magnetic field from the pinned layer, but if it is facing in the opposite direction, it receives a magnetic field from the pinned layer in a destabilizing direction, so it is necessary to design a free layer that is more resistant to thermal fluctuations. .

  On the other hand, the capacity of a hard disk or MRAM is basically determined by the bit size or cell size. When the size is reduced, the problem of thermal fluctuations occurs, so that expectation for multi-value recording is increasing. For example, Patent Document 3 discloses a structure in which a total of two magnetic recording layers are inserted between three magnetic reference layers. This is a technique for recording / reproducing using only current.

Furthermore, a technique for reading multi-value information by applying a magnetic field during reproduction is disclosed (Patent Document 4). According to this, by inserting an in-plane type free layer between two in-plane magnetic recording layers and applying an external magnetic field to rotate the magnetization of the free layer, The relative angle (parallel or antiparallel) is read. In the case of this structure, since the magnetization is in-plane, if the external magnetic field is to be applied, it is necessary to use the above-mentioned write line, and there is a problem in place selectivity. For this reason, it is said that it is difficult to apply to an MRAM having about 64 Mbits or more. Further, the recording method is not disclosed.
FJ Albert, et al., Appl. Phy. Lett. 77, 3809 (2000) Japanese Patent Laid-Open No. 2005-93488 JP 2004-193595 A JP 2004-193595 A JP 2004-356642 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic memory capable of multi-value recording and having good thermal stability, a writing method thereof, and a reproducing method.

  The magnetic memory according to the first aspect of the present invention includes a first ferromagnetic layer, a first nonmagnetic layer formed on the first ferromagnetic layer, and a second formed on the first nonmagnetic layer. A memory cell having a ferromagnetic layer, a second nonmagnetic layer formed on the second ferromagnetic layer, and a third ferromagnetic layer formed on the second nonmagnetic layer; Each of the first and third ferromagnetic layers has an easy axis of magnetization substantially perpendicular to the film surface, and the second ferromagnetic layer has a smaller coercive force and an easy axis of magnetization than the first and third ferromagnetic layers. It is characterized in that it is inclined at an angle of greater than 0 degree and not more than 90 degrees with respect to a direction perpendicular to the film surface.

  The magnetic memory reproducing method according to the second aspect of the present invention is the magnetic memory reproducing method according to the first aspect, wherein electrons are caused to flow from the first ferromagnetic layer to the second ferromagnetic layer. And changing the magnetization direction of the second ferromagnetic layer and measuring the resistance according to the relative magnetization directions of the second and third ferromagnetic layers. Detecting the direction of magnetization of the magnetic layer.

The magnetic memory reproducing method according to the third aspect of the present invention is the magnetic memory according to the first aspect, wherein the magnetic memory is electrically connected from the third ferromagnetic layer side of the memory cell and connected to the memory cell. The magnetic probe further includes a magnetic probe capable of relative movement and capable of changing the direction of its own magnetization, and the magnetization of the second ferromagnetic layer is substantially perpendicular to the film surface according to the direction of magnetization of the magnetic probe. A method of reproducing a magnetic memory controlled to be directed in a direction, wherein the magnetization direction of the second ferromagnetic layer is oriented in a direction substantially perpendicular to the film surface by adjusting the magnetization direction of the magnetic probe; and , By passing a current between the first ferromagnetic layer and the third ferromagnetic layer using the magnetic probe, and an electrical resistance between the first ferromagnetic layer and the second ferromagnetic layer, and 2 ferromagnetic layers and the third strength Characterized in that it comprises the steps of: reading the sum of the electrical resistance between the sexual layer.
A magnetic memory writing method according to a fourth aspect of the present invention is the magnetic memory according to the first aspect, wherein the magnetic memory is electrically connected to the third ferromagnetic layer and is relative to the third ferromagnetic layer. The magnetic probe further includes a magnetic probe capable of moving and capable of changing the direction of its own magnetization, and the magnetization of the second ferromagnetic layer is in a direction substantially perpendicular to the film surface in accordance with the direction of magnetization of the magnetic probe. A method of writing to a magnetic memory controlled so as to be directed to the direction of magnetization of the second ferromagnetic layer by adjusting the direction of magnetization of the magnetic probe; and The direction of magnetization of the first ferromagnetic layer or the third ferromagnetic layer into which electrons have flowed by flowing electrons from the second ferromagnetic layer toward the first ferromagnetic layer or the third ferromagnetic layer. Of the second ferromagnetic layer Characterized in that it comprises the steps of: varying so as to have the same orientation as the reduction.

  According to the present invention, it is possible to provide a magnetic memory capable of multi-value recording and having good thermal stability, a writing method thereof, and a reproducing method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
First, a magnetic memory according to a first embodiment of the present invention will be described. The magnetic memory according to the present embodiment has a plurality of memory cells arranged in a matrix. A basic configuration of the memory cell according to the present embodiment is shown in FIGS. The memory cell 1 includes a first magnetic recording layer 2 having a ferromagnetic layer, a first barrier layer 4, a magnetic reference layer 6 having a ferromagnetic layer, a second barrier layer 8, and a second magnetic having a ferromagnetic layer. The recording layer 10 has a stacked structure in which the recording layers 10 are stacked in this order. The magnetic recording layers 2 and 10 are layers for storing information, and the magnetic reference layer 6 is a reference layer for recording and reproducing information on the magnetic recording layers 2 and 10.

By making the easy axis directions of magnetization of the first and second magnetic recording layers 2 and 10 (in the magnetic recording layers 2 and 10 the magnetization is perpendicular to the film surface when there is no external magnetic field) to be the direction perpendicular to the film surface The magnetization orientation direction is perpendicular to the film surface. Here, the film surface means the surface of the film when the first or second magnetic recording layer 2, 10 is regarded as a “film”. Accordingly, the direction perpendicular to the film surface means that the first magnetic recording layer 2, the nonmagnetic first barrier layer 4, the magnetic reference layer 6, the nonmagnetic second barrier layer 8, and the second magnetic recording layer 10. It becomes the direction of stacking. The first and second magnetic recording layer 2 and 10, the uniaxial magnetic anisotropy constant K _u, for example, perpendicular magnetization material having a 1 × 10 6 ^erg / cc or more values used generally perpendicular magnetization film both Called. That is, the first and second magnetic recording layers 2 and 10 have a magnetization direction substantially perpendicular to the film surface when there is no external magnetic field. The perpendicular magnetization film is easier to miniaturize than the in-plane magnetization film in which the magnetization direction is substantially parallel to the film surface in the absence of an external magnetic field, and the current of the spin injection current for magnetization reversal is small and power saving.

On the other hand, the magnetic reference layer 6 is configured to have a lower coercive force than the first and second magnetic recording layers 2 and 10. That is, the magnetic reference layer 6 has a uniaxial magnetic anisotropy constant K _u or a crystal anisotropy constant K ₁ of, for example, 1 × 10 ⁵ erg / cc or less, and the easy axis direction alone is 0 with respect to the film surface perpendicular. A material that is tilted at an angle greater than 90 degrees and less than 90 degrees is selected.

In order to make the easy magnetization directions of the first and second magnetic recording layers 2 and 10 perpendicular to the film surface, the saturation magnetization M _s (emu / cc) of the magnetic material constituting the magnetic recording layer is different. The relationship with the isotropic magnetic field H _an (Oe) may be set to Han> 12.57 Ms. Incidentally, the anisotropic magnetic field _{H an,} using the magnetic anisotropy _{K u} direction perpendicular to the film plane _is given by _{H an = 2K u / M s} .

  In the memory cell 1 configured as described above, when the magnetizations of the first and second magnetic recording layers 2 and 10 are parallel (in the same direction), the magnetization of the magnetic reference layer 6 is shown in FIG. Thus, the magnetization directions of the first and second magnetic recording layers 2 and 10 are the same. On the other hand, as shown in FIG. 1B, when the magnetizations of the first and second magnetic recording layers 2 and 10 are antiparallel (opposite directions), the magnetization of the magnetic reference layer 6 is on the film surface. It becomes almost parallel.

  A specific example of the memory cell according to this embodiment is shown in FIG. The memory cell 1 of this specific example includes a first magnetic recording layer 2, a first magnetic insertion layer 12, a first barrier layer 4, a second magnetic insertion layer 14, a magnetic reference layer 6, a third magnetic insertion layer 16, and a second magnetic recording layer. The barrier layer 8, the fourth magnetic insertion layer 18, and the second magnetic recording layer 10 have a stacked structure in which they are stacked in this order. That is, the first and second magnetic insertion layers 12 and 14 are provided so as to sandwich the first barrier layer 4 of the memory cell 1 shown in FIGS. 1A and 1B, and the second barrier layer 8 is sandwiched therebetween. Thus, the third and fourth magnetic insertion layers 16 and 18 are provided. Note that it is not necessary to provide all of the first to fourth magnetic insertion layers. For example, only the first and fourth magnetic insertion layers 12 and 18 in contact with the first and second magnetic recording layers 2 and 10 may be provided.

  The stacked structure of the memory cell 1 is provided on a metal underlayer 22 formed on the soft magnetic underlayer 20. For example, the magnetic recording layer 2 includes FePt (5 nm), the first magnetic insertion layer 12 includes an Fe—Co alloy (1.5 nm), the first barrier layer 4 includes MgO (1.5 nm), and the second magnetic layer. The insertion layer 14 has an Fe—Co alloy (1.5 nm), the magnetic reference layer 6 has NiFe (10 nm), the third magnetic insertion layer 16 has an Fe—Co alloy (1.5 nm), and the second barrier layer 8 has Is MgO (2.5 nm), the fourth magnetic insertion layer 18 is Fe-Co alloy (1.5 nm), and the second magnetic recording layer 10 is FePt (15 nm). Ru (3 nm) is formed as the cap layer 19 on the second magnetic recording layer 10. The numbers in parentheses indicate the layer thickness. The laminated structure in which these layers are laminated is processed into a cylinder having a diameter of 20 nm. This cylinder is called a memory cell 1. Under the memory cell 1, a Ta layer (1 nm) is formed as a metal underlayer 22, and a Ni—Fe alloy layer (50 nm) is formed as a soft magnetic underlayer 20 thereunder.

  In the magnetic memory of this embodiment, the metal base layer 22 is shared, and a plurality of cells 1 are formed in contact with each other. For example, another cell 1 is formed at a distance of 10 nm. . That is, the magnetic memory according to this embodiment has a configuration in which the memory cells 1 are arranged in a matrix with the metal base layer 22 in common.

  In the magnetic memory of this embodiment, as shown in FIG. 3, the magnetic probe 30 runs on the memory cells 1 arranged in a matrix. The magnetic probe 30 has a structure like an SPM probe, for example, and can energize the magnetic probe 30 by energizing an excitation coil 32 connected to the magnetic probe 30. The magnetic probe 30 is formed of, for example, a Fe—Co—Ni-based metal magnetic material (saturation magnetization amount is 1.5 T), and is processed to have a diameter (tip) closest to the memory cell 1, that is, a tip diameter of 30 nm. ing. The tip surface may be coated with a hard conductive carbon film in order to improve lubrication with the memory cell 1.

  FIG. 4 shows current paths of the memory cell 1 and the magnetic probe 30. The magnetic probe 30 has a function of conducting current for recording and reproduction by contacting the cap layer 19 of each memory cell 1 and a function of changing the magnetization direction of the magnetic reference layer 6 of the memory cell 1. A DC voltage is applied to the magnetic probe 30, and current can be passed between the memory cell 1 and the metal underlayer 22 and the soft magnetic underlayer 20 that each memory cell 1 uses as a common electrode. That is, the current supplied from the magnetic probe 30 flows from the cap layer 19 of the memory cell 1 through the memory cell 1 to the ground electrode composed of the metal underlayer 22 / soft magnetic underlayer 20. Alternatively, the magnetic probe 30 may be set to a negative potential by setting the power supply voltage, and the reverse path may be taken. A coil 32 is wound around the magnetic probe 30, and the magnetization direction M of the magnetic probe 30 can be made upward or downward by changing the direction in which the coil 32 is energized. Although not shown in FIG. 4, as shown in FIG. 5, the magnetic probe 30 is provided with a return yoke 36 made of, for example, NiFe having a thickness of 100 nm on the upper surface (the surface opposite to the memory cell 1). The magnetic flux emitted from the tip of the magnetic probe 30 passes through the memory cell 1 and forms a magnetic path that returns to the return yoke 36 through the soft magnetic underlayer 20. Therefore, a strong magnetic field can be supplied concentrated on the memory cell 1.

The dependence on the first and second magnetic recording layers 2 and 10 regarding the magnetization state of the magnetic reference layer 6 can be considered as follows. FIG. 6 shows an MH curve in a direction perpendicular to the film surface, measured by a sample vibration magnetometer (VSM) of the magnetic reference layer 6 itself. Although it has perpendicular anisotropy, the magnetic reference layer 6 itself does not exhibit the saturation magnetization M _s in the absence of a magnetic field, and is biased to the position of M _ap . As shown in FIG. 7, when the second magnetic recording layer 10 (magnetization M _p2 ) and the first magnetic recording layer 2 (magnetization M _p1 ) are antiparallel, the second magnetic recording layer 10 flows into the magnetic reference layer 6. the magnetic field (H _p2) that is, mutual and a magnetic field (H _p1) that flows from the first magnetic recording layer 2 to the magnetic reference layer 6 is canceled, since a state in which a bias is not applied is shown in FIG. 6 M- The bias point comes to the position of M _ap on the H curve.

On the other hand, as shown in FIG. 8, when the second magnetic recording layer 10 (magnetization M _p2 ) and the first magnetic recording layer 2 (magnetization M _p1 ) are parallel, the magnetic fields H _p2 from the magnetic recording layer 6, H _p1 strengthens and is biased to the point M _p shown in FIG. 6 by the total H _b of H _p1 and H _p2 . FIG. 9 is a diagram showing a comparison of MH curves between the magnetic recording layer and the magnetic reference layer. The magnetic recording layer has a configuration in which magnetization reversal does not occur even when the magnetic reference layer is saturated.

Recording Method Next, a method for recording in the memory cell 1 of the magnetic memory of this embodiment will be described.

  First, a method for recording the magnetization of the magnetic reference layer 6 upward will be described. The coil 32 of the magnetic probe 30 in contact with the upper surface of the cap layer 19 of a certain memory cell 1 is energized, and the magnetization M of the magnetic probe 30 is recorded in the direction to be recorded (in this case, the magnetization of the magnetic reference layer 6 is recorded upward). So turn upward). As a result, only the magnetization of the magnetic reference layer 6 having a small anisotropic energy is directed upward. This can be controlled by the saturation magnetization of the magnetic probe 30, the distance from the soft magnetic underlayer (not shown), and the coercivity of the first and second magnetic recording layers 2 and 10.

(1) Reversal of magnetization of the first magnetic recording layer 2
The magnetization of the first magnetic recording layer changes from upward to downward. An example in which the magnetization of the first magnetic recording layer 2 is reversed from upward to downward will be described with reference to FIG. A direction in which the magnetization M of the magnetic probe 30 faces downward and electrons flow from the magnetic reference layer 6 to the magnetic recording layer to be recorded (in this case, electrons from the magnetic reference layer 6 toward the first magnetic recording layer 2). Energize to flow). By making the direction of the magnetization M of the magnetic probe 30 downward, the magnetization direction of the magnetic reference layer 6 faces downward. Further, electrons are caused to flow from the magnetic reference layer 6 to the first magnetic recording layer 2 (current is caused to flow from the magnetic reference layer 6 to the magnetic probe 30), whereby downward spin is generated from the magnetic reference layer 6 to the first magnetic recording layer 2. The magnetization of the first magnetic recording layer 2 receives a downward torque due to the spin transfer effect. Furthermore, since the magnetization of the first magnetic recording layer 2 is assisted by the magnetic field from the magnetic probe 30 and the magnetic reference layer 6, it can rotate quickly with a low current. In FIG. 10A, symbol ST represents a spin transfer torque applied to the magnetic recording layer 2 by electrons coming from the magnetic reference layer 6, and symbol H represents a magnetic field torque applied to the magnetic recording layer 2 by the magnetic reference layer 6 and the magnetic probe 30. . Further, the symbol “+” indicates a situation in which the assist is made in the desired direction, and the symbol “−” indicates a situation in which it acts in an unstable direction. FIG. 10A shows that for the first magnetic recording layer 2, the spin transfer torque ST and the magnetic field torque H due to the magnetic field are both in an assist state (that is, in a direction in which recording is easy). Further, since the magnetic field is continuously applied, the magnetization of the magnetic reference layer 6 is not rotated by the upward spin electrons reflected from the first magnetic recording layer 2.

  By the way, in the second magnetic recording layer 10 facing the same direction as the magnetic reference layer 6, the spin transfer torque ST is "-" and the magnetic field torque H is "+". The upward spin electrons (arrow A in the figure) reflected by the magnetic reference layer 6 generate a torque that reverses the magnetization direction of the second magnetic recording layer 10 upward (ST-). However, the current for changing the magnetization of the second magnetic recording layer 10 from parallel to antiparallel to the magnetization of the magnetic reference layer 6 causes the magnetization of the first magnetic recording layer 2 to be parallel to the magnetic reference layer 6. It is usually about 1.5 to 2 times larger than the case of inversion (that is, recording action). Furthermore, since assistance from the magnetic probe 30 is added so that the magnetization of the second magnetic recording layer 10 does not rotate (H +), the magnetization of the second magnetic recording layer 10 is in a stable state in the downward direction. Recording can be performed on the first magnetic recording layer 2. In FIG. 10A, the second magnetic recording layer 10 is in the same direction as the magnetic reference layer 6.

  On the other hand, as shown in FIG. 10B, when the second magnetic recording layer 10 faces upward, the magnetic field torque from the magnetic probe 30 acts in a direction that makes the second magnetic recording layer 10 unstable (H +). . However, the torque due to the upward spin reflected by the magnetic reference layer 6 acts in a direction to stabilize the magnetization direction of the second magnetic recording layer 10 upward (ST +). Therefore, the spin transfer torque ST and the magnetic field torque H always contribute to the easy recording direction (ST +, H +) in the first magnetic recording layer 2 to be written, whereas the second magnetic recording layer 10 in which writing is not desired. The spin transfer torque ST and the magnetic field H are +/− or − / +, and at least one of them works in the direction of stabilization. Therefore, it can be seen that the first magnetic recording layer 2 in which both torques assist each other is more easily recorded. This will be described using an MH curve shown in FIG. Since a magnetic field H that magnetizes the magnetic reference layer 6 in the vertical direction is added, and the spin transfer torque ST contributes to the first magnetic recording layer with a plus, the total magnetic field (converted) contributes to the coercive force of the first magnetic recording layer 2. As a result, the magnetization of the first magnetic recording layer 2 is reversed. On the other hand, since the second magnetic recording layer 10 returns from the applied magnetic field H by “ST−”, it becomes a stable state and does not invert.

The case where the magnetization of the first magnetic recording layer is changed from downward to upward will be described with reference to FIGS. 12A and 12B in which the magnetization of the first magnetic recording layer 2 is reversed from downward to upward. The magnetization of the magnetic reference layer 6 is directed upward with the direction of the magnetic probe 30 upward, and electrons are caused to flow from the magnetic reference layer 6 into the layer to be rewritten. This case can be achieved by allowing the magnetic reference layer 6 to flow into the first magnetic recording layer 2. The influence of the spin transfer torque ST and the magnetic field torque H on the second magnetic recording layer 10 is shown in FIG. 12A where the magnetization of the second magnetic recording layer 10 is opposite to the magnetization M of the magnetic probe 30. This corresponds to the case shown in FIG. 10B, and the case of FIG. 12B in the same direction corresponds to the case shown in FIG. Therefore, when the magnetization of the first magnetic recording layer 2 is reversed from the downward direction to the upward direction, only the first magnetic recording layer 2 is stably stabilized, as in the case where the magnetization of the first magnetic recording layer 2 is reversed from the upward direction to the downward direction. Can be recorded.

(2) Reversal of Magnetization of Second Magnetic Recording Layer 10 A case where the magnetization of the second magnetic recording layer 10 is reversed will be described with reference to FIGS. 13 (a) and 13 (b). Energization is performed in a direction in which electrons flow from the magnetic reference layer 6 to the second magnetic recording layer 10 to be recorded. 10 (a), 10 (b), 12 (a), and 12 (b), the same action as when recording the first magnetic recording layer 2 works on the second magnetic recording layer 10. FIG. 13A shows a case where the magnetization of the first magnetic recording layer 2 is upward and in the same direction as the magnetization of the magnetic reference layer 6, and FIG. 13B is a magnetic reference where the magnetization of the first magnetic recording layer 2 is downward. The case of the direction opposite to the magnetization of the layer 6 is shown. Regarding the second magnetic recording layer 10, the spin transfer torque ST is “+” and the magnetic field torque H is “+”, and the magnetization rotation is stably performed at a low current and quickly (recorded). In the case shown in FIG. 13A, the first magnetic recording layer 2 has a spin transfer torque ST of “−” and a magnetic field torque H of “+”. In the case shown in FIG. Since the transfer torque ST is “+” and the magnetic field torque H is “−”, the unstable state of one of the two torques is canceled by the other torque. Therefore, when recording the second magnetic recording layer 10 upward and downward (not shown), the spin transfer ST and the magnetic field torque H are applied to the second magnetic recording layer 10 with assistance, and the spin transfer ST is antiparallel. → Since parallel recording, recording can be performed at a low current. Directing the magnetic reference layer 6 in the direction in which recording is desired always has an antiparallel → parallel spin transfer action. For this reason, recording is performed by spin transfer, and the anti-parallel → parallel (small current), parallel → anti-parallel (large current) as in a general MRAM having one magnetic reference layer and one magnetic recording layer. Compared with the above operation, it is possible to design a power-saving memory cell having a small current density. For this reason, it is possible to increase the output by increasing the thickness of the barrier layer to improve the S / N.

  Thus, recording can be performed individually on the first and second magnetic recording layers 2 and 10 by using three magnetic layers, that is, one magnetic reference layer 6. By combining these recording methods, the multi-value recording can be performed in four directions, ie, upper, upper, lower, upper, lower and lower, of the magnetization directions of the first and second magnetic recording layers 2 and 10. For example, after changing the magnetization direction of one of the first magnetic recording layer 2 or the second magnetic recording layer 10 to be the magnetization direction of the magnetic reference layer 6, the magnetization direction of the magnetic probe 30 is adjusted. If the direction of the magnetization of the magnetic reference layer 6 is reversed and the direction of the electron flow is reversed to reverse the direction of the other of the first and second magnetic recording layers 2, 10, Four types of multi-value recording can be performed: upper, upper, lower, upper, lower and lower.

  In the magnetic memory of the present embodiment, the magnetic field supply means 30 such as an SPM probe (Scanning Probe Microscope (SPM)) is shown. However, the magnetic probe 30 is a normal HDD in which the main magnetic pole is energized. When a commercially available HDD head is used, a DC current can be supplied to the main magnetic pole, the current is supplied to the recording coil to control the magnetization direction of the main magnetic pole, and the DC current is supplied to the tip of the magnetic pole. The multi-valued recording of the first embodiment can be performed by flowing it from the cell to the cell, and it is desirable if a head capable of thermally controlling the amount of protrusion of the recording coil main pole by the energization current is obtained. For example, K. Ise, S. Takahashi, K. Yamakawa, and N. Honda, “New Shielded Single-Pole Head with Planar Structure,” IEEE Trans. Magn., 42, 2422-2424, (2006).) Flat head In it may be traveling planar head. Planar head can be recorded by the multi-probe because it can form many of the main magnetic pole i.e. magnetic probe in a plane.

  The magnetic memory according to the present embodiment is overwhelming in the so-called side erase (side fringing) resistance, that is, recording to a medium in a normal HDD and writing to an adjacent bit as compared with a bit patterned medium (BPM) structure. Excellent. This is because the recording is based on spin current using magnetic field assist. Since recording is performed only on a memory cell in which a current density of a certain level or more flows, it is not necessary to attach a shield for the main magnetic pole, which improves the efficiency of magnetic flux emission and saves power by reducing the coil current. be able to. Further, as described in the magnetic probe 30 in FIG. 3, the current is supplied from the contact portion between the tip of the magnetic probe and the memory cell, whereas the magnetic field is further emitted from the trapezoidal side wall portion over a wide range. It is also applied to adjacent memory cells. The magnetic probe shape in which the magnetic field is distributed over a wide range as described above is advantageous in terms of energy saving because the magnetic field intensity per unit current can be increased. However, since recording is performed only on the memory cell through which a current flows, the recording resolution does not deteriorate. The tip size of the main pole is ideally the same as the cell plane area but may be large. For example, when the barrier layers 4 and 8 are made of a metal material and have a CPP-GMR (Current Perpendicular Plane-Giant Magneto-Resistance) structure, the resistance of the memory cell can be designed to be small. Contact resistance with the cell. In this case, since a current proportional to the contact area flows through the memory cell, even if the planar shape of the magnetic probe 30 is configured to supply current across a plurality of memory cells 1 as shown in FIG. Recording can be performed only on the most overlapping part. Therefore, the manufacturing process of the magnetic probe 30 is facilitated, and the system can be configured at a low cost.

Normal State In the magnetic memory of this embodiment, as shown in FIG. 3, it can be seen that the magnetization direction of the magnetic reference layer 6 in the memory cell where the magnetic probe 30 is not on the upper surface of the memory cell 1 is not uniform. For example, in the memory cell 1a (memory cell 1d) in which the magnetization of the second magnetic recording layer 10 is upward (downward) and the magnetization of the first magnetic recording layer 2 is downward (upward), the magnetization of the magnetic reference layer 6 is Face in the plane. On the other hand, in the memory cell 1c (memory cell 1b) in which the magnetization of the second magnetic recording layer 10 is upward (downward) and the magnetization direction of the first magnetic recording layer 2 is upward (downward), the magnetic reference layer 6 Magnetization is substantially perpendicular to the plane. In this embodiment, when not affected by the magnetic probe 30, it is designed not to form a magnetic layer in which perpendicular magnetizations face each other as shown in FIGS. 15 (a) and 15 (b). . A laminated structure in which a magnetic layer 201 and a magnetic layer 203 are laminated with a nonmagnetic layer 202 interposed therebetween as shown in FIG. 15A, or a magnetic layer 201, a nonmagnetic layer 202 as shown in FIG. In the case of a laminated structure in which the magnetic layer 203, the nonmagnetic layer 204, and the magnetic layer 205 are laminated, the magnetizations of the magnetic layer 201 and the magnetic layer 203 are opposed to each other with the nonmagnetic layer 202 interposed therebetween. In this case, since a bias magnetic field is applied from each magnetic layer to each other, it is necessary to impart a larger magnetic anisotropy to each magnetic layer in order to maintain thermal stability, which complicates the process design. It will lead to cost increase. Therefore, in the present embodiment, the magnetic reference layer 6 is sandwiched between the first and second magnetic recording layers 2 and 10 via the barrier layers 4 and 8, and the first and second magnetic recording layers 2 and 10 are sandwiched. The magnetic reference layer 6 is designed so that the magnetization of the first and second magnetic recording layers 2 and 10 and the magnetization of the magnetic reference layer 6 do not oppose each other when the two magnetizations face each other.

On the other hand, when the magnetizations of the first and second magnetic recording layers 2 and 10 are in the same direction, the effective magnetic volume increases when the magnetic coupling is performed in the same direction, so that the thermal stability is improved. improves. Therefore, when the magnetizations of the first and second magnetic recording layers 2 and 10 are in the same direction, the magnetization of the magnetic reference layer 6 is designed so as to be easily oriented in a substantially vertical direction. For this purpose, it is desirable that the magnetic reference layer 6 is thick and has a small saturation magnetization. For example, if the memory cell size is 20 nm in diameter and the film thickness is about 7 nm and the film thickness / diameter ratio is 1/3, the demagnetizing factor is about 1/2. Therefore, when the saturation magnetization amount of the magnetic reference layer 6 is 1T and a magnetic field of about 1/2 of 5 kOe is applied, the magnetization of the magnetic reference layer 6 comes to face in the vertical direction. If a bias magnetic field of about 1 kOe to 2 kOe is applied from the first and second magnetic recording layers 2 and 10 from the FePt layer, the magnetization of the magnetic reference layer 6 is directed in a substantially vertical direction in addition to the original perpendicular magnetic anisotropy. It becomes like this. However, even if it does not face completely in the perpendicular direction, there is an effect because it is possible to substantially reduce the influence caused by the magnetic charges appearing at the edges of the first and second magnetic recording layers 2 and 10. A great effect can be exhibited if the adjacent and opposing magnetization states as shown in FIGS. 15 (a) and 15 (b) are not created. Therefore, when the magnetizations of the first and second magnetic recording layers 2 and 10 face each other, even if the magnetization of the magnetic reference layer 6 is in the in-plane direction, Since the distance between 10 increases as the thickness of the magnetic reference layer 6 increases, a great effect is exhibited. In general, the demagnetizing factor in the thickness direction d, the saturation magnetization of the magnetic reference layer 6 and Ms, uniaxial magnetic anisotropy constant in the direction perpendicular to the film plane of the magnetic reference layer 6 K _u or crystal magnetic anisotropy The isotropic constant K is expressed by the following formula (1) (1/2) dMs ² > K _u (1)
Is satisfied, the magnetization direction of the magnetic reference layer 6 deviates from perpendicular to the film surface and exhibits an effect.

Reproduction Method Next, a reproduction method will be described with reference to FIGS. 16 (a1) to 16 (d2). 16 (a1), FIG. 16 (b1), FIG. 16 (c1), and FIG. 16 (d1) are diagrams showing four combinations of magnetization states in the first and second magnetic recording layers 2 and 10. 16 (a2), FIG. 16 (b2), FIG. 16 (c2), and FIG. 16 (d2) are the cases shown in FIG. 16 (a1), FIG. 16 (b1), FIG. 16 (c1), and FIG. It is a figure which shows each resistance value of these.

  FIG. 16A1 shows a magnetization state in which the magnetization of the second magnetic recording layer 10 is downward and the magnetization of the first magnetic recording layer 2 is upward. The coil 32 of the magnetic probe 30 is energized, and the upward and downward magnetization M is excited in the magnetic probe 30. Accordingly, a magnetic field is applied to the magnetic reference layer 6, and the magnetization of the magnetic reference layer 6 is directed upward and downward. Therefore, when the magnetization of the magnetic reference layer 6 is upward, the resistance value between the magnetic probe 30 through the memory cell 1 and the common magnetic underlayer serving as the ground is the magnetization of the second magnetic recording layer 10. It becomes an antiparallel state, becomes parallel to the magnetization of the first magnetic recording layer 2, and becomes a combined resistance. As shown in FIG. 16 (a2), the magnetization directions of the first magnetic recording layer 2 and the magnetic reference layer 6 are antiparallel, and the magnetization directions of the second magnetic recording layer 10 and the magnetic recording layer 6 are parallel. A memory cell in which the resistance of the memory cell 1 is R1, the magnetization directions of the first magnetic recording layer 2 and the magnetic reference layer 6 are parallel, and the magnetization directions of the second magnetic recording layer 10 and the magnetic recording layer 6 are antiparallel. The resistance of the memory cell 1 when the resistance of 1 is R2, the magnetization directions of the first magnetic recording layer 2 and the magnetic reference layer 6 are parallel, and the magnetization directions of the second magnetic recording layer 10 and the magnetic recording layer 6 are parallel. Is R0, the resistance value R2 when the magnetization of the magnetic reference layer 6 is upward, and the resistance value R1 when the magnetization is downward, as shown in FIG. 16 (a2). Note that the arrows in FIG. 16A2 indicate the magnetization direction of the magnetic reference layer 6. Therefore, by changing the magnetic field applied from the magnetic probe 30 up and down, the combination of the resistances of the two barrier layers 4 and 8 in the antiparallel case can be determined. At this time, if the current is smaller than the critical recording current value (the current value that does not change the magnetization direction of the magnetic reference layer 6 or the first and second magnetic recording layers), the magnetic probe 30 moves to the magnetic underlayer as shown in the figure. It may flow in the opposite direction or in the opposite direction.

  Further, in FIG. 16B1, FIG. 16C1, and FIG. 16D1, combinations of magnetizations of the second magnetic recording layer 10 and the first magnetic recording layer 2 are (downward, downward), (upward, 16 (b2), FIG. 16 (c2), and FIG. 16 (d2) are shown in FIG. 16 (b1), FIG. 16 (c1), and FIG. In the case of 16 (d1), the resistance values when the magnetization of the magnetic reference layer 6 is upward and downward are shown. In FIG. 16 (b1), FIG. 16 (c1), and FIG. 16 (d1), the magnetic probe 30 is omitted. Also, FIG. 16 (b2). The arrows in FIGS. 16C2 and 16D2 indicate the direction of magnetization of the magnetic reference layer 6.

  In the case shown in FIG. 16 (b2), when the magnetization of the magnetic reference layer 6 is upward, the magnetization of the magnetic reference layer 6 is antiparallel to the magnetization of the first and second magnetic recording layers 2 and 10. The resistance value of the memory cell 1 is R1 + R2. On the other hand, when the magnetization of the magnetic reference layer 6 is downward, the magnetization of the magnetic reference layer 6 is parallel to the magnetization of the first and second magnetic recording layers 2 and 10. , R0.

  The case shown in FIG. 16 (c2) is opposite to the case shown in FIG. 16 (b2). When the direction of magnetization of the magnetic reference layer 6 is upward, the resistance value of the memory cell 1 is R0, and when it is downward The resistance value of the memory cell 1 is R1 + R2.

  In the case shown in FIG. 16 (d2), the reverse state of the case shown in FIG. 16 (a2) appears. When the magnetization direction of the magnetic reference layer 6 is upward, the resistance value of the memory cell 1 is R1, and when it is downward, the resistance value of the memory cell 1 is R2.

  As described above, by applying an upper and lower magnetic field to the magnetic reference layer 6 from the magnetic probe 30 and reading the resistance value in that case, the four combinations of magnetization directions of the magnetic recording layers 2 and 10 can be read. .

  Next, a method for speeding up the reproduction in the magnetic memory of this embodiment will be described with reference to FIGS. 17 (a1) to 17 (d2). 17 (a1), FIG. 17 (b1), FIG. 17 (c1), and FIG. 17 (d1) are diagrams showing four combinations of magnetization states in the first and second magnetic recording layers 2 and 10. 17 (a2), FIG. 17 (b2), FIG. 17 (c2), and FIG. 17 (d2) are the cases shown in FIG. 17 (a1), FIG. 17 (b1), FIG. 17 (c1), and FIG. It is a figure which shows each resistance value of these. This method is a method in which only the upward magnetization M is excited in the magnetic prober 30 in order to increase the speed during reproduction.

  When the magnetization directions of the first and second magnetic recording layers 2 and 10 are different, that is, in the cases shown in FIGS. 17A1 and 17D1, the magnetization of the magnetic reference layer 6 is substantially parallel to the film surface. Turn to the direction. However, when the magnetization directions of the first and second magnetic recording layers 2 and 10 are the same, the magnetization of the magnetic reference layer 6 is perpendicular to the film surface in the cases of FIGS. 17B1 and 17C1. The direction is slightly inclined from the direction. As shown in FIGS. 17 (a2), 17 (b2), 17 (c2), and 17 (d2), the magnetic probe 30 is not excited until a certain time t1, and excitation is started at the time t1. is there. Note that the arrows shown in FIGS. 17A2, 17B2, 17C2, and 17D2 indicate the direction of magnetization of the magnetic reference layer 6.

  16 (a2), FIG. 16 (b2), FIG. 16 (c2), and FIG. 16 (d2) show a static state of 10 ns or more, and FIG. 17 (a2), FIG. 17 (b2), FIG. 17 (c2) and FIG. 17 (d2) show a transient state (˜1 ns) in which the magnetization of the magnetic reference layer 6 is reversed, so that a gradient is given to the resistance. When excitation of the magnetic probe 30 is started at time t1, in the case shown in FIG. 17A2, the magnetization of the magnetic reference layer 6 is horizontal (substantially parallel to the film surface). It increases from the intermediate resistance of R2 toward the resistance R2. The intermediate state of the resistors R1 and R2 indicates that the magnetizations of the first and second magnetic recording layers 2 and 10 are in an antiparallel state, and application of an upward magnetic field from the magnetic probe 30 to the magnetic reference layer 6 is started. The increase in resistance to the resistance value R2 indicates that the second magnetic recording layer 10 and the magnetic reference layer 6 are in an antiparallel state. On the other hand, from the same intermediate state, when the upward magnetic field is applied, the resistance value decreases and becomes the resistance value R1, which indicates that the magnetization of the first magnetic recording layer 2 is downward. That is, the first and second magnetic recording layers 2, 10 can be determined depending on whether the initial resistance value is known and thereafter the increase starts (in the case shown in FIG. 17 (a 2)) or the decrease starts (FIG. 17 (d 2)). This shows the magnetization state of.

  Similarly, the fact that the initial state is intermediate between the resistance value R1 and the resistance value R0 indicates that the magnetizations of the first and second magnetic recording layers 2 and 10 are in the same direction (FIG. 17B1). 17 (b2), FIG. 17 (c1), FIG. 17 (c2)), and after the magnetic probe 30 is excited, it rises toward the resistance value R1 + R2 in the cases shown in FIG. 17 (b1) and FIG. 17 (b2). There is a decrease in the resistance value R0 in the cases shown in FIGS. 17 (d1) and 17 (d2). Also in this case, if the initial state and the subsequent resistance change direction are known, the magnetization states of the first and second magnetic recording layers 2 and 10 can be known. By doing in this way, it is possible to reproduce approximately one digit faster than the reproduction using the static state as shown in FIGS. 16 (a1) to 16 (d2).

  In a known example (Japanese Patent Laid-Open No. 2004-356642) in which the magnetization direction is parallel to the film surface, it is difficult to apply a magnetic field locally when the size is about 20 nm. Furthermore, when the direction of magnetization is parallel to the film surface, it is almost impossible to impart an effective large anisotropy to the magnetic reference layer in a certain direction within the film surface. It is almost impossible to execute the reproduction method as shown in FIGS. 17A1 to 17D2 that uses a certain degree of deviation from the vertical direction.

  In the present embodiment, when the first and second magnetic recording layers 2 and 10 have the same information (magnetization direction), for example, in the case of (upward, upward), (downward, downward), weak magnetic anisotropy. Is designed so that the magnetization thereof is substantially oriented in the same direction as the magnetizations of the first and second magnetic recording layers 2 and 10. For this reason, the first and second magnetic recording layers 2 and 10 and the magnetic reference layer 6 are the same as a series of long magnets, and instability due to heat is reduced. On the other hand, when the magnetizations of the first and second magnetic recording layers 2 and 10 are directed in opposite directions, for example, in the case of (upward or downward) or (downward or upward), the magnetic reference layer 6 is in the lateral direction (film In the direction substantially parallel to the surface) and works to escape the magnetic flux from the first and second magnetic recording layers 2 and 10, or the distance between the surface magnetizations of the first and second recording layers is the same as the magnetic reference layer. By spreading it, the bias magnetic fields of each other can be reduced. Therefore, instability due to heat is reduced even if the magnetizations of the first and second magnetic recording layers 2 and 10 are directed in opposite directions. As a result, a thermally stable magnetic memory can be provided.

  In addition, since it is possible to record and reproduce information in the first and second magnetic recording layers 2 and 10 while applying a magnetic field, multi-value can be achieved and a larger capacity magnetic memory is provided. be able to.

  As described above, according to this embodiment, a magnetic memory capable of multi-value recording can be obtained. Further, when the current is not energized, the magnetization of the magnetic reference layer 6 deviates from the perpendicular to the film surface and does not form an antiparallel state with the first and second magnetic recording layers 2 and 10, so that the thermal stability is excellent.

(Second Embodiment)
Next, a magnetic memory according to a second embodiment of the present invention will be described with reference to FIGS. 18 (a1) to 18 (d2).

  The magnetic memory according to the present embodiment has a configuration in which the magnetic probe 30 is deleted from the magnetic memory according to the first embodiment. As in the first embodiment, the memory cell 1 includes a first magnetic recording layer 2, a first barrier layer 4, a magnetic reference layer 6, a second barrier layer 8, and a second magnetic recording layer 10 stacked in this order. It has a laminated structure. In addition, as shown in FIG. 2, the magnetic insertion layers 12, 14, 16, and 18 may be provided above and below the first and second barrier layers 4 and 8, respectively. Electrodes (not shown) are arranged above and below the memory cell 1, and current can be supplied to the memory cell. The direction of the current can flow both upward and downward.

  The first magnetic recording layer 2 is FePt (5 nm), the magnetic insertion layer 12 is Fe—Co alloy (1.5 nm), the first barrier layer 4 is MgO (1.5 nm), and the magnetic insertion layer 14 is Fe. -Co alloy (1.5 nm), TbFeCo (5 nm) for the magnetic reference layer 6, Fe-Co alloy (1.5 nm) for the magnetic insertion layer 16, alumina (2.5 nm) for the second barrier layer 8, An Fe—Co alloy (1.5 nm) is used for the magnetic insertion layer 18, and FePt (15 nm) is used for the second magnetic recording layer 10. Further, Ru (3 nm) is formed as a cap layer 19 on the upper part, and these laminated films are processed into a cylinder having a diameter of 30 nm.

The uniaxial magnetic anisotropy constant K _u of the magnetic reference layer 6 is designed to be 1 × 10 ⁶ erg / cm ³ or less, and the magnetization is directed obliquely in a non-energized state. In addition, the spin transfer effect is designed so as to have a large effect between the first magnetic recording layer 2 and the magnetic reference layer 6. For this reason, the first barrier layer 4 is composed of MgO (1.5 nm), the second The barrier layer 8 is alumina (2.5 nm). The magnetization reversal of the magnetic reference layer 6 due to the spin transfer effect causes electrons to flow from the magnetic reference layer 6 to the first magnetic recording layer 2 at a certain critical current or more, so that the magnetization of the magnetic reference layer 6 changes to the first magnetic recording layer 2. It becomes antiparallel to the magnetization of. Conversely, when electrons flow from the first magnetic recording layer 2 to the magnetic reference layer 6, the magnetization of the magnetic reference layer 6 is parallel to the magnetization of the first magnetic recording layer.

  Next, a reproducing method of the magnetic memory according to the present embodiment will be described with reference to FIGS. 18 (a1) to 18 (d2).

  FIG. 18 (a1) is a diagram showing the magnetization directions and the flow of electrons in the first and second magnetic recording layers 2, 10 and the magnetic reference layer 6, and FIG. 18 (a2) shows the change in resistance value at that time. FIG. The magnetization information of the second magnetic recording layer 10 is upward and the magnetization of the first magnetic recording layer 2 is downward. Electrons are supplied from upper and lower electrodes (not shown) to flow electrons from the first magnetic recording layer 2 toward the second magnetic recording layer. The magnetization of the magnetic reference layer 6 is in the lateral direction when no current is applied or the critical current value is below. When energization is started at time t1, information in the first magnetic recording layer 2 is copied to the magnetic reference layer 6 by the spin transfer effect, and the magnetization of the magnetic reference layer 6 is directed downward. At this time, the magnetization of the magnetic reference layer 6 is parallel to the magnetization of the first magnetic recording layer and is antiparallel to the magnetization of the second magnetic recording layer 10, so that the resistance of the memory cell 1 is R2.

  FIG. 18B1 shows a state in which the magnetizations of the first and second magnetic recording layers 2 and 10 are antiparallel, and electrons flow from the magnetic reference layer 6 to the first magnetic recording layer 2. As shown in FIG. 18 (b1), by flowing electrons as described above, the magnetization of the magnetic reference layer 6 facing in the lateral direction (direction substantially parallel to the film surface) is changed with the first magnetic recording layer 2. It indicates that the magnetization is antiparallel to the first magnetic recording layer 2 by facing upward due to the spin transfer effect. FIG. 18B2 shows that the resistance value approaches the resistance value R1 from time t1 when the critical current value starts to flow. This resistance value R1 is the resistance of the memory cell 1 when the magnetization of the magnetic reference layer 6 is antiparallel to the magnetization of the first magnetic recording layer 2 and parallel to the magnetization of the second magnetic recording layer 10. The value is shown. Note that the same characteristics as in FIG. 18B2 are obtained when the magnetization of the second magnetic recording layer 10 is downward and the magnetization of the first magnetic recording layer 2 is upward.

  FIG. 18C1 shows a case where the magnetizations of the first and second magnetic recording layers 2 and 10 are in a downward state. The magnetization of the magnetic reference layer 6 in the direction deviating from the perpendicular to the film surface is directed upward by a spin transfer effect by energizing the magnetic reference layer 6 so that electrons flow from the magnetic reference layer 6 to the first magnetic recording layer 2. It shows that the second magnetic recording layers 2 and 10 are in an antiparallel state with the magnetization. In that case, as shown in FIG. 18C2, the resistance of the memory cell 1 changes from a value between the resistance value R0 and the resistance value R1 to a state of R1 + R2.

  Conversely, in the state shown in FIGS. 18 (d1) and 18 (d2), the magnetizations of the first and second magnetic recording layers 2 and 10 face upward, and the magnetization of the magnetic reference layer 6 deviated from the film surface perpendicularity. Is directed upward by causing electrons to flow from the first magnetic recording layer 2 to the magnetic reference layer 6 and is parallel to the magnetizations of the first and second magnetic recording layers 2 and 10, and the resistance of the memory cell 1 has a resistance value R0.

  As described above, according to the present embodiment, the magnetization state of the multi-valued memory cell can be read only by the direction of the current, and the magnetization of the magnetic reference layer 6 is deviated from the film surface perpendicular when no current is applied. Thus, the first and second magnetic recording layers 2 and 10 do not form an anti-parallel state, so that the thermal stability is excellent.

Next, materials of the magnetic reference layer and the magnetic recording layer in the first and second embodiments described above will be described.
The magnetic reference layer and the magnetic recording layer are, for example, magnetic metals containing one or more elements selected from the group of Fe (iron), Co (cobalt), Ni (nickel), Mn (manganese), and Cr (chromium) It consists of.

For the magnetic recording layer, one or more elements selected from the group of Fe, Co, Ni, Mn, and Cr, Pt (platinum), Pd (palladium), Ir (iridium), Ru (ruthenium), Rh ( When the alloy in combination with one or more elements selected from the group of rhodium), a uniaxial magnetic anisotropy constant K _u of the magnetic recording layer is increased and 1 × 10 7 ^erg / cc or so, the perpendicular magnetic recording It will be suitable. The value of the uniaxial magnetic anisotropy constant K _u, the composition and of the magnetic material constituting the magnetic recording layer can be adjusted by such crystalline regularity due to heat treatment.

  The magnetic reference layer may be composed of, for example, a rare earth-transition metal amorphous alloy such as TbFeCo or GdFeCo, or a Co / Pt laminated structure.

  The magnetic material constituting the magnetic recording layer and the magnetic reference layer can be a continuous magnetic material or a composite structure in which fine particles made of a magnetic material are deposited in a matrix in a nonmagnetic material.

On the other hand, the magnetic insertion layer is, for example, one of Fe (iron), Co (cobalt), Ni (nickel), or Fe (iron), Co (cobalt), Ni (nickel), Mn (manganese), It is comprised from the alloy containing one element selected from the group of Cr (chromium). The magnetic insertion layer is made of soft magnetic material such as CoNbZr, FeTaC, CoTaZr, FeAlSi, FeB, CoFeB, Heusler alloy such as Co ₂ MnSi, CrO ₂ , Fe ₃ O ₄ , La _1-x Sr _x MnO _3, etc. A half-metal oxide or nitride, or a magnetic semiconductor may be used.

  Next, the nonmagnetic barrier layer will be described. The two types of low resistance material and high resistance material will be described.

For the nonmagnetic barrier layer, an insulating material can be used as a tunnel barrier layer for obtaining a large reproduction signal output by the TMR (tunnel magneto resistive) effect at the time of reading. Specifically, Al (aluminum), Ti (titanium), Zn (zinc), Zr (zirconium), Ta (tantalum), Co (cobalt), Ni (nickel), Si (silicon), Mg (magnesium), The nonmagnetic barrier layer can be composed of an oxide, nitride, or fluoride containing at least one element selected from the group of Fe (iron). In particular, the nonmagnetic barrier layers are Al ₂ O _3-x (0 <x <3, alumina), MgO (magnesium oxide), SiO _2-x (0 <x <2), Si—O—N, Ta. It is preferably composed of —O, Al—Zr—O, ZnOx, TiO _x , or a group III-V compound semiconductor (GaAlAs or the like) having a large energy gap.

  In addition, for non-magnetic barrier layers, a nanocontact MR (magneto resistive) material in which a magnetic material is inserted into a pinhole provided in an insulator, or Cu is inserted into a pinhole provided in an insulator. A large reproduction signal output can be obtained by using a CPP (current-perpendicular-to-plane) -CPP-MR material.

  When the nonmagnetic barrier layer is a tunnel barrier layer, the thickness is preferably set to a value in the range of 0.2 nm to 2.0 nm in order to obtain a large reproduction signal output. Similarly, when the nonmagnetic barrier layer is a nanocontact MR material, the thickness is preferably set to a value within the range of 0.4 nm to 40 nm in order to obtain a large reproduction signal output.

1 is a perspective view showing a basic configuration of a memory cell according to an embodiment of the present invention. FIG. 3 is a cross-sectional view showing a specific example of a memory cell according to an embodiment of the present invention. 1 is a perspective view showing a magnetic memory according to a first embodiment. FIG. 3 is a diagram for explaining a current path of the memory cell according to the first embodiment. FIG. 3 is a diagram for explaining a magnetic circuit of the memory cell according to the first embodiment. FIG. 4 is a diagram showing an MH curve of the memory cell according to the first embodiment. FIG. 3 is a view for explaining magnetization of a memory cell according to the first embodiment. FIG. 3 is a view for explaining magnetization of a memory cell according to the first embodiment. The figure which shows the MH curve of a magnetic reference layer and a magnetic-recording layer in 1st Embodiment. FIG. 3 is a diagram for explaining a memory cell recording method according to the first embodiment. FIG. 6 is a diagram for explaining that the memory cell recording method according to the first embodiment is stable. FIG. 3 is a diagram for explaining a memory cell recording method according to the first embodiment. FIG. 3 is a diagram for explaining a memory cell recording method according to the first embodiment. The figure which shows the relationship between the size of a magnetic probe, and the size of a memory cell. The figure explaining the problem when the direction of magnetization of a magnetic layer is in the opposing state. FIG. 3 is a diagram for explaining an example of a memory cell reproduction method according to the first embodiment. FIG. 6 is a diagram for explaining another example of the memory cell reproducing method according to the first embodiment. FIG. 6 is a diagram for explaining an example of a method for reproducing a memory cell according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Memory cell 2 1st magnetic recording layer 4 1st barrier layer 6 Magnetic reference layer 8 2nd barrier layer 10 2nd magnetic recording layer 12 Magnetic insertion layer 14 Magnetic insertion layer 16 Magnetic insertion layer 18 Magnetic insertion layer 19 Cap layer 20 Soft Magnetic underlayer 22 Metal underlayer 30 Magnetic probe 32 Excitation coil

Claims (8)

A first ferromagnetic layer;
A first nonmagnetic layer formed on the first ferromagnetic layer;
A second ferromagnetic layer formed on the first nonmagnetic layer;
A second nonmagnetic layer formed on the second ferromagnetic layer;
A third ferromagnetic layer formed on the second nonmagnetic layer;
A memory cell having
A magnetic probe electrically connected to the memory cell from the third ferromagnetic layer side, capable of relative movement with respect to the memory cell, and capable of changing the direction of its magnetization;
With
The first and third ferromagnetic layers each have an easy axis of magnetization perpendicular to the film surface;
The second ferromagnetic layer has a smaller coercive force than the first and third ferromagnetic layers, and the easy axis of magnetization is inclined at an angle of greater than 0 degree and less than 90 degrees with respect to a direction perpendicular to the film surface. And
The magnetic memory characterized in that the magnetization of the second ferromagnetic layer is controlled to be perpendicular to the film surface and to a direction corresponding to the magnetization direction of the magnetic probe by a magnetic field applied from the magnetic probe. . When the magnetizations of the first and third ferromagnetic layers are opposite to each other, the second ferromagnetic layer is oriented in a direction parallel to the film surface,
2. The magnetic memory according to claim 1, wherein when the magnetizations of the first and third ferromagnetic layers are in the same direction, the magnetization of the second ferromagnetic layer is in a direction perpendicular to the film surface. A first ferromagnetic layer; a first nonmagnetic layer formed on the first ferromagnetic layer; a second ferromagnetic layer formed on the first nonmagnetic layer; and the second ferromagnetic layer A memory cell having a second nonmagnetic layer formed on the second nonmagnetic layer and a third ferromagnetic layer formed on the second nonmagnetic layer, wherein the first and third ferromagnetic layers are respectively on the film surface. Having a perpendicular easy axis, the second ferromagnetic layer has a smaller coercive force than the first and third ferromagnetic layers, and an easy axis of magnetization is greater than 0 degree with respect to the direction perpendicular to the film surface A method of reproducing a magnetic memory tilted at an angle of 90 degrees or less,
Changing the direction of magnetization of the second ferromagnetic layer by allowing electrons to flow from the first ferromagnetic layer to the second ferromagnetic layer;
Detecting a magnetization direction of the first ferromagnetic layer by measuring a resistance due to a relative magnetization direction of the second ferromagnetic layer and the third ferromagnetic layer;
A method for reproducing a magnetic memory, comprising: When the magnetizations of the first and third ferromagnetic layers are opposite to each other, the second ferromagnetic layer is oriented in a direction parallel to the film surface,
4. The method of reproducing a magnetic memory according to claim 3, wherein when the magnetizations of the first and third ferromagnetic layers are in the same direction, the magnetization of the second ferromagnetic layer is in a direction perpendicular to the film surface. . A method of reproducing a magnetic memory according to claim 1 or 2,
Directing the magnetization of the second ferromagnetic layer in a direction perpendicular to the film surface by adjusting the direction of magnetization of the magnetic probe;
By passing a current between the first ferromagnetic layer and the third ferromagnetic layer using the magnetic probe, an electric resistance between the first ferromagnetic layer and the second ferromagnetic layer, and the second Reading the sum of the electrical resistance between the ferromagnetic layer and the third ferromagnetic layer;
A method for reproducing a magnetic memory, comprising: Reversing the magnetization direction of the second ferromagnetic layer perpendicular to the film surface by adjusting the magnetization of the magnetic probe;
Reading the relative magnetization directions of the first and third ferromagnetic layers before and after the reversal of the magnetization of the second ferromagnetic layer;
The method of reproducing a magnetic memory according to claim 5, further comprising: The method of writing in a magnetic memory according to claim 1 or 2,
Adjusting the magnetization direction of the magnetic probe to direct the magnetization of the second ferromagnetic layer in a direction perpendicular to the film surface;
By flowing electrons between the first ferromagnetic layer and the third ferromagnetic layer through the second ferromagnetic layer in a state where a magnetic field from the magnetic probe is applied, the first ferromagnetic layer And among the third ferromagnetic layers, the magnetization direction of the ferromagnetic layer into which electrons have flowed through the second ferromagnetic layer is changed to be the same direction as the magnetization of the second ferromagnetic layer. Steps,
A magnetic memory writing method comprising: After changing the magnetization direction of one of the first ferromagnetic layer or the third ferromagnetic layer to be the magnetization direction of the second ferromagnetic layer, the magnetization direction of the magnetic probe is adjusted. The direction of the magnetization of the second ferromagnetic layer is reversed and the direction of electron flow is reversed in a state where the magnetic field from the magnetic probe is applied, and the other one of the first and third ferromagnetic layers is reversed. 8. The magnetic memory writing method according to claim 7 , further comprising the step of reversing the direction of magnetization.

Images