JPH08255707A - Magnetic body and magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a new magnetic body indicating diamagnetic-ferromagnetic change due to the irradiation with light and a magnetic recording medium using it. CONSTITUTION: A magnetic body is expressed by a general expression, Bi2-x Pbx Sr2-y REy MnO6+b (0.8<=x<=1.2, RE: at least one type of rare earth elements La, Nd. Eu, Ce, Sm, and Pr, 0<=y<=0.2, d: excessive oxygen) and develops ferromagnetism by irradiation with light or electric field and a magnetic recording medium uses the magnetic body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic material and a magnetic recording medium using the magnetic material.

[0002]

2. Description of the Related Art In recent years, magnetic recording has dramatically improved its recording density due to improvements in the performance of recording media. Various systems have been studied as a magnetoresistive effect element for reproducing this high-density recorded information. Among them, the head using the magnetoresistive effect corresponds to high recording density,
It is expected that a reproduced signal with high SN can be obtained. In particular, the giant magnetoresistive effect found in a metal superlattice formed by stacking magnetic metal / nonmagnetic metal is attracting attention as a new technology that brings breakthrough performance improvement in this field.

More recently, in a superlattice composed of a laminated film of a magnetic metal and a semiconductor, the magnetic coupling between the magnetic metal layers is changed by exciting electron-hole pairs in the semiconductor layer by light irradiation,
It was found that an antiferromagnetic-ferromagnetic change occurs.
This phenomenon is that while conventional magneto-optical recording is performed by utilizing the temperature rise due to light irradiation, the photon energy of the irradiation light can be directly used, so that a higher speed and higher density recording method can be provided. It is also expected to be used as various new sensors.

[0004]

However, the above-mentioned magnetic metal / semiconductor superlattice which exhibits antiferromagnetic-ferromagnetic change by light irradiation has complicated manufacturing conditions and is not suitable for large-scale production. However, it is difficult to directly apply this to magnetic recording and the like because the change in magnetization due to photoexcitation is also small.

In addition to this, there are only limited combinations for producing a magnetic metal / semiconductor superlattice, and the degree of freedom in design has been low. The present invention has been made in consideration of the above problems, and provides a novel magnetic substance exhibiting a change in antiferromagnetic-ferromagnetic property due to light irradiation and the like, and a magnetic recording medium using the same. With the goal.

[0006]

Means and Action for Solving the Problems The magnetic substance according to claim 1 of the present invention is a layered oxide of B ₂ Sr ₂ MnO _{6 + d} .
A general formula Bi _2-x Pb _x Sr _2-y RE _y M in which a part of i is replaced with Pb and a part of Sr is replaced with a rare earth element
nO _{6 + d} (0.8 ≦ x ≦ 1.2, RE is a rare earth element L
at least one of a, Nd, Eu, Ce, Sm and Pr,
0 ≦ y ≦ 0.2, d is excess oxygen), and is characterized by exhibiting ferromagnetism by light irradiation or application of an electric field.

The magnetic substance according to claim 2 is the oxide LaMn.
A general formula in which a part of La of O ₃ is replaced with Sr, La _1-x S
It is represented by r _x MnO ₃ (0 ≦ x ≦ 0.2) and is characterized by exhibiting ferromagnetism by light irradiation or application of an electric field.

The present invention uses these magnetic materials as the invention according to claim 3, wherein a layer containing a magnetic material which exhibits ferromagnetism by light irradiation and a recording holding layer are laminated. A magnetic recording medium characterized by the above.

Further, as a fourth aspect of the present invention, there is provided a magnetic recording medium characterized in that a layer containing a magnetic body exhibiting ferromagnetism by applying an electric field and a dielectric layer are laminated. To do.

Oxide having a layered structure Bi ₂ Sr ₂ Mn
Replacing part of Bi in O _{6 + d} with Pb lowers the resistance value, for example, Physica C167 (1990) 2
0-34.

The inventor of the present invention, by substituting a part of Sr of this oxide with a rare earth element, is doped with a low-concentration thermal equilibrium carrier, and then is irradiated with light to excite the excited electrons and positive electrons. It was found that the transition from the antiferromagnetic state to the ferromagnetic state occurs via holes, and the transition temperature at this time reaches room temperature or higher. It was also found that the manifestation of this ferromagnetic state occurs even when light irradiation is performed without performing Sr / rare earth element substitution.

Further, in a thin film in which the above substance is laminated with a ferroelectric substance such as BaTiO3 or a high dielectric constant substance such as SrTiO3, charge injection into a magnetic substance is caused by dielectric polarization generated by applying an electric field to this laminated film. It was also found that the magnetic properties occurred and the magnetic properties changed.

One of the magnetic materials according to the present invention is Bi-Cu oxide B, which is well known as a copper oxide high temperature superconductor.
It has the same crystal structure as i ₂ Sr ₂ CuO ₆ and its copper site is completely replaced by Mn as a matrix. This substance is an antiferromagnetic material having a transition temperature (Neil point) of 130K, and the composition obtained by substituting 50% of Bi with Pb is also an antiferromagnetic material having a Neel point of 150K.

As mentioned above, the present inventors
When a part of Sr is replaced with Pb, a part of Sr is further added to a certain rare earth element (La, Nd, Eu, Ce, Sm,
It is possible to carry out so-called thermal equilibrium carrier doping by substituting at least one selected from Pr), and in the case where the substitution amount is small in this system, or the thermal equilibrium carrier doping by Sr / rare earth element substitution is not carried out, that is, the system When the carrier concentration is lower than that which shows perfect ferromagnetism, it is found that ferromagnetism develops when photoexcited carriers are generated by irradiating it with excitation light having sufficient energy. It was This corresponds to the fact that the photon energy of the excitation light directly changes the magnetic characteristics, and is considered to be a so-called new phenomenon called photoinduced ferromagnetism. This phenomenon continues during irradiation of the excitation light, and a new concept of magneto-optical recording (in the conventional so-called magneto-optical writing is performed by the temperature rise by light, in this case, the photon mode is used) It provides a new material that can be industrially applied to a magnetic head.

Also, the high transition temperature to the ferromagnetic state is rare in this kind of oxide magnetic material, and is extremely useful industrially. Here, the mechanism of manifestation of this photoinduced ferromagnetism will be briefly described.

Normal configuration, ie magnetic metal (MM)
In a magnetic metal superlattice formed by stacking a nonmagnetic metal (NM) and a magnetic metal (MM), conduction carriers existing in thermal equilibrium are responsible for magnetic coupling between MM layers.

On the other hand, Z. Phys. B92, 13
7 (1993), Phys. Rev. Lett. , 7
1, 185 (1993), magnetic metal (MM) -nonmagnetic semiconductor (SC) -magnetic metal (M).
The photo-induced ferromagnetism recently reported in the superlattice formed by stacking M) is considered to be that the photocarriers generated in the SC by light irradiation are responsible for the magnetic coupling between the MMs.
The detailed mechanism of the photo-induced ferromagnetism of the Bi—Mn oxide according to the present invention has not been clarified so far, but like the MM-SC-MM superlattice, it is thermally excited by photoexcitation. It is believed that the momentum of Mn ions is bound by nonequilibrium conduction carriers.

The Bi / Pb substitution carried out here changes the electronic state of the magnetic material according to the present invention and is extremely effective for the expression of photoinduced ferromagnetism. In order to exhibit ferromagnetic coupling by double exchange mediated by carriers generated by photoexcitation, it is necessary that the effective mass m ^* of these carriers be sufficiently small and have some itinerary. Therefore, the band width of the conduction band and the valence band of the material used in the present invention needs to be sufficiently large.

The inventor of the present invention has found that Bi / Pb substitution changes the crystal structure of this substance, flattens the electric conduction surface formed by Mn and oxygen, thereby expanding the band width, and iterating the electronic state of the system. Found to be effective for. In addition, the expansion of the band width of these bands also brings about a decrease in the band gap, and has the effect of exhibiting photoexcited ferromagnetism by exciting sufficient carriers even by using excitation light of lower energy.

When this substance is used as a photoinduced magnetic material, the range of 0.8 ≦ x ≦ 1.2 is desirable. When it is less than 0.8, the manifestation of the ferromagnetic state is insufficient when light irradiation is performed, and when it is more than 1.2, precipitation of impurity heterophase components is caused.

Thus, the Bi / Pb substitution is effective in increasing the band width and making the electronic state of the system favorable for the photoinduced ferromagnetism manifestation, but at this time, the thermal equilibrium carrier concentration does not change. Therefore, the thermal equilibrium carrier concentration of the system can be independently changed by substituting rare earth for Sr. That is, in this system, the bandwidth and band gap of the system and the thermal equilibrium carrier concentration can be adjusted independently, and the application as a photoinduced magnetic material can be freely selected by changing the content of rare earth. Has become. This change in the amount of rare earth does not affect the crystal structure or the lattice parameter. Therefore, when creating a laminated film of a ferromagnetic layer or a dielectric layer and a photoinduced magnetic layer, which will be described later, there is a problem of lattice mismatch. Can be easily avoided.

The amount of the rare earth element to be replaced is preferably in the range of 0≤y≤0.2, since the presence of excess heat equilibrium carrier is harmful. As described above, the layered Bi-Mn oxide according to the present invention has a feature that the band width or band gap and the thermal equilibrium carrier concentration can be changed independently, and is a substance suitable for application as a photoinduced magnetic substance. is there.

On the other hand, when Mn oxide LaMnO ₃ having a non-layered perovskite structure is replaced with an element, an antiferromagnetic material is changed to a ferromagnetic metal by ferromagnetic coupling (double exchange) mediated by injected conduction carriers. It is conventionally known that changes occur. This oxide is La
Injecting carriers by substituting a part of Sr with Sr simultaneously decreases the band gap and increases the thermal equilibrium carrier concentration.

The present inventor has found that even in this substance, when the Sr substitution amount is small, that is, when the number of thermal equilibrium carriers is small and the ferromagnetic property is weak, the magnetic property is changed by light irradiation. It was found that can be applied as a photo-induced magnetic material. In this case, the disadvantage is that the bandgap cannot be controlled independently, but it can be used as a practical photoinduced oxide magnetic material by appropriately selecting the energy of the excitation light.

As in the case of the layered Bi-Mn oxide, a ferroelectric such as BaTiO ₃ or SrTiO 3 is used.
It was also found that in a thin film laminated with a high-dielectric constant material such as ₃ above, charge injection into a magnetic substance occurs due to dielectric polarization generated by applying an electric field to this laminated film, and the magnetic characteristics change.

By the way, the above-described photoinduced magnetic material according to the present invention has a drawback that when it is used as a recording medium by photoexcitation, its magnetization disappears when the light irradiation is stopped.

In order to solve this problem, the present inventor has
As a result of extensive studies, it was found that by laminating a magnetic film having an appropriate coercive force as a recording holding layer with this photoinduced magnetic film, the magnetization generated by light irradiation can be retained even after irradiation is stopped. It was

Various materials can be used for the magnetic material used for the recording holding layer, but it is preferable to use an oxide magnetic material from the viewpoint of compatibility with the photoinduced magnetic material according to the present invention. Further, as a photo-induced magnetic material, a layered Bi-Mn
When oxides or LaMn oxides are used, Bi _2-x Pb _x Sr _2-y RE _y MnO _{6 + d} is used as the recording holding layer.
(0.6 ≦ x ≦ 1.2, 0.2 ≦ y ≦ 0.5), La
_{The use of 1-x} Mn _x O ₃ (0.25 ≦ x <0.6) is the most desirable from the viewpoint of the consistency between layers.

At this time, the thickness of the photoinduced magnetic layer and the recording holding layer can be set arbitrarily, but if the respective film thicknesses are too thin, sufficient photoinduced magnetism and coercive force cannot be obtained. If the film thickness is too large, the absorption of the excitation light makes it impossible to utilize sufficient photoinduced magnetism over the entire film. Therefore, the film thickness of these layers is 10 nm to 1000 n.
It is desirable to be in the range of m.

Various methods can be used for the recording / reproducing method, but a magneto-optical method using a substance having a large magneto-optical effect in the recording holding layer or a magnetoresistive effect utilizing the magnetization of the recording layer is used. Is preferable from the viewpoint of recording density.

The photo-induced magnetic material exhibits a ferromagnetic state by photoexcited carriers, and also exhibits a ferromagnetic characteristic by charge injection by dielectric polarization when an electric field is applied, for example, in a laminated film with a dielectric. . At this time, if a ferroelectric material such as BaTiO3 is used as the dielectric material to be used, the remanent polarization generated by applying an electric field higher than the coercive electric field to the dielectric material holds the developed ferromagnetic characteristics, so that the voltage application is performed. Write information by
It is also possible to create a storage device that reads information by changing the magnetic resistance or the magneto-optical effect.

Also in this case, the film thickness of the magnetic layer or the dielectric layer can be set arbitrarily, but the charge injection due to the dielectric polarization is a phenomenon that occurs near the interface between the dielectric and the magnetic body. If the film thickness is too large, the change in the characteristics due to polarization, that is, the effect of the apparent dielectric polarization, on the magnetization and the magnetic resistance of the entire film becomes small. Further, if these film thicknesses are too thin, the crystallinity of the film deteriorates, and the original magnetic characteristics and dielectric characteristics cannot be obtained. Therefore, the film thickness of these layers is preferably in the range of 10 nm to 1000 nm.

The magnetic material according to the present invention does not have a complicated structure such as a superlattice / multilayered film, can be easily prepared, and has a large change in magnetic characteristics upon irradiation with light. It can be applied to various sensors such as density magnetic recording media and magnetic heads. Further, in the case of a layered Bi-Mn oxide, the magnetic transition temperature is high, and therefore industrial application is easy.

[0034]

Embodiments of the present invention will be described below. Bi _2-x As (Example 1) Example 1 Pb _x Sr _2-y L
A thin film of a photo-induced magnetic material having a composition of a _y MnO _{6 + d} (x = 1.0, y = 0.05) was formed on an STO substrate by RF magnetron sputtering to a thickness of 500 nm, and the quan was formed.
The sample was inserted into a sample holder with an optical fiber manufactured by tum Design Co., Ltd. and attached to a SQUID magnetic susceptometer manufactured by Quantum Design Co., Ltd.

At this time, the results of measuring the magnetization with and without irradiation of the excitation light of the laser light of wavelength 60 nm (output 100 mW) at room temperature over a magnetic field of -5T to + 5T are shown in FIG. In the figure, the point 1 indicates that light is emitted, and the solid line 2 indicates that light is not emitted.

As shown in the figure, when light is not irradiated, it exhibits a small paramagnetic magnetization, whereas when it is irradiated with light, the magnetization is about ± 4 emu / g, which is a ferromagnetic material having a large hysteresis. Show the behavior.

When the photoresponse of magnetoresistance of this film was measured in a magnetic field of 0.01 T, the resistance value of the film was 1 by light irradiation.
It changed to / 100 and was found to be usable as an optical sensor or an optical switch. (Example 2) As Example 2, a magnetic recording medium was prepared using the photoinduced magnetic material according to Example 1. FIG. 2 shows a cross-sectional view thereof.

On the STO substrate 3, a thin film of the magnetic material having the composition of Example 1 was formed as the photoinduced magnetic material layer 4 by RF magnetron sputtering, and further, as the recording holding layer 5, Bi _{2-x.
Pb x Sr 2-y La y} MnO 6 + d (x = 1.0, y =
The oxide magnetic material having the composition
A film was formed with a film thickness of 0 nm, and this lamination sequence was repeated 30 times to prepare a magnetic recording medium 6 having a recording holding layer 5. The photo-induced magnetic layer 4 and the recording holding layer 5 of this magnetic recording medium 6 were covered with a protective layer 7 made of SiO ₂ .

Under a room temperature environment, a recording portion on a spot excited by a laser beam having a wavelength of 60 nm was prepared in a magnetic field of 100 gauss, and the recording portion was reproduced by using a magneto-optical effect. As a result, it was found that the recording spot was retained even after the photoexcitation was stopped, and this laminated film had suitable properties as a magnetic recording medium. (Example 3) As Example 3, La _1-x Sr _x MnO ₃
A thin film of a photo-induced magnetic layer having a composition (x = 0.1) is deposited on an STO substrate by RF magnetron sputtering to 500n.
m film is formed, and this is inserted into the sample holder with optical fiber manufactured by Quantum Design Co.
It was attached to a SQUID susceptibility meter manufactured by tum Design. At this time, laser light with a wavelength of 60 nm (output 100
The magnetization with and without irradiation with (mW) excitation light was measured at room temperature over a magnetic field of −5T to + 5T. The results are similar to those shown in FIG. 1, and show a paramagnetic small magnetization when not irradiated with light, but exhibit a ferromagnetic behavior with large hysteresis when irradiated with light. (Example 4) As Example 4, a magnetic recording medium was prepared using the photoinduced magnetic material according to Example 3. The sectional view has the same structure as that in FIG.

A thin film of a magnetic material having the composition of Example 3 was formed on the STO substrate 3 as the photo-induced ferromagnetic material layer 4 by RF magnetron sputtering, and the recording holding layer 5 was formed of L.
An oxide magnetic material having a composition of a _1-x Sr _x MnO ₃ (x = 0.4) was formed into a film with a film thickness of 200 nm, and the lamination sequence was repeated 30 times, and the recording holding layer 5 was formed.
A magnetic recording medium having This magnetic recording medium 6
The photo-induced magnetic layer 4 and the recording holding layer 5 were covered with a protective layer 7 made of SiO ₂ .

Under a room temperature environment, a recording portion on a spot excited by a laser beam having a wavelength of 60 nm was created in a magnetic field of 100 gauss, and the recording portion was reproduced by using a magneto-optical effect. As a result, it was found that the recording spot was retained even after the photoexcitation was stopped, and this laminated film had suitable properties as a magnetic recording medium. (Example 5) As Example 5, a magnetic recording medium different from those of Examples 2 and 4 was prepared. The sectional view is shown in FIG.

STO: Bi _2-x Pb _x Sr _2-y La _y MnO _{6 + d} (x
= 1.0, y = 0.05), a thin film is formed by RF magnetron sputtering, and the dielectric layer 10
As a magnetic recording medium 11, an oxide magnetic material having a composition of Ba _0.5 Sr _0.5 TiO ₃ was formed to a film thickness of 1000 A, and the sequence was repeated 10 times. At this time, it was confirmed by X-ray diffraction and the like that each layer was epitaxially grown.

In this case, Ba _0.5 Sr of the dielectric layer 10 is
_0.5 TiO ₃ is a ferroelectric substance at room temperature due to lattice distortion, and the polarization formed by applying an electric field is preserved even if the electric field is removed.

On the uppermost dielectric layer 10 of the magnetic recording medium 11, a metal film such as Al is formed as the upper electrode 12, and a resistance detection terminal 13 is formed on the side surface of the electric field induction magnetic layer 9 / dielectric layer 10. Then, a protective film 14 made of SiO ₂ was formed so as to fill the space between the upper electrode 12 and the resistance detection terminal 13. As a result, a memory device was created in which a recording operation was performed by applying a voltage between the upper electrode 11 and the STO: Nb substrate 8.

Charge injection resulting from polarization charges induced by application of an electric field is caused by Bi _2-x Pb in the electric field induced magnetic layer 9.
_{x Sr 2-y La y MnO} 6 + d (x = 1.0, y = 0.0
5), this layer exhibits ferromagnetic properties. The change at this time is read by the change in the magnetic resistance accompanying the change in the magnetic characteristics of the film. The electric resistance of this film when the dielectric was not polarized was 10 ₃ Ωcm, whereas the electric resistance when the dielectric was polarized showed a large change of 10 ₁ Ωcm, confirming the memory operation.

Further, when the change in magnetization depending on the presence or absence of polarization of this film was measured, it was found that the magnetic susceptibility was low when the dielectric was not polarized, whereas the magnetic susceptibility was large when the dielectric was polarized. It was also found that it can be used as a magnetic read type recording medium. (Example 6) As Example 6, a magnetic recording medium having the same structure as that of Example 5 was prepared.

On the STO: Nb substrate 8, a thin film having a composition of La _1-x Sr _x MnO ₃ (x = 0.1) was formed as an electric field induction magnetic layer 9 by RF magnetron sputtering.
Further, as the dielectric layer 10, Ba _0.5 Sr _0.5 TiO _{3 is used.}
An oxide magnetic material having the following composition was formed into a film having a film thickness of 100 nm, and this sequence was repeated 10 times to prepare a magnetic recording medium 11. At this time, it was confirmed by X-ray diffraction and the like that each layer was epitaxially grown.

In this case, the dielectric layer Ba _0.5 Sr _0.5 Ti
O ₃ is a ferroelectric substance at room temperature due to lattice distortion,
The polarization formed by applying an electric field is preserved even if the electric field is removed.

On the uppermost dielectric layer 10 of the magnetic recording medium 11, a metal film such as Al is formed as the upper electrode 12, and a resistance detection terminal 13 is formed on the side surface of the electric field induction magnetic layer 9 / dielectric layer 10. Then, a protective film 14 made of SiO ₂ was formed so as to fill the space between the upper electrode 12 and the resistance detection terminal 13. As a result, a memory device was created in which a recording operation was performed by applying a voltage between the upper electrode 11 and the STO: Nb substrate 8.

The charge injection resulting from the polarization charge induced by the application of the electric field is caused by the La _{1 -x} Sr of the electric field induced magnetic layer 9.
generated in _{x MnO 3 (x = 0.1)} , this layer exhibits a ferromagnetic properties. The change at this time is read by the change in the magnetic resistance accompanying the change in the magnetic characteristics of the film. The electric resistance of this film when the dielectric is not polarized is 10 ₂ Ωcm, while the electric resistance when the dielectric is polarized is 1
There was a large change of Ωcm, and the memory operation was confirmed.

Further, when the change in the magnetization of this film depending on the presence or absence of polarization was measured, it was found that the magnetic susceptibility was low when the dielectric was not polarized, whereas the magnetic susceptibility was large when the dielectric was polarized. It was also found that it can be used as a magnetic read type recording medium.

[0052]

As described above, according to the present invention, it is possible to provide a novel magnetic substance exhibiting an antiferromagnetic-ferromagnetic change due to light irradiation and the like, and a magnetic recording medium using the same.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a magnetic field dependence of a magnetic body according to a first embodiment of the invention.

FIG. 2 is a sectional view of a magnetic recording medium according to Examples 2 and 4 of the invention.

FIG. 3 is a sectional view of a magnetic recording medium according to Examples 5 and 6 of the present invention.

[Explanation of symbols]

3, 8 ... Substrate; 4 ... Photoinduced magnetic layer; 5 ... Recording holding layer;
6, 11 ... Magnetic recording medium; 9 ... Electric field induced magnetic material layer; 10
... Dielectric layer

Claims (4)

[Claims] 1. A B of a layered oxide Bi ₂ Sr ₂ MnO _{6 + d} .
A general formula Bi _2-x Pb _x Sr _2-y RE _y M in which a part of i is replaced with Pb and a part of Sr is replaced with a rare earth element
nO _{6 + d} (0.8 ≦ x ≦ 1.2, RE is a rare earth element L
at least one of a, Nd, Eu, Ce, Sm and Pr,
0 ≦ y ≦ 0.2, d is excess oxygen), and exhibits ferromagnetism by light irradiation or application of an electric field. 2. A part of La of the oxide LaMnO ₃ is added to Sr.
With the general formula La _1-x Sr _x MnO ₃ (0 ≦ x ≦
0.2), which exhibits ferromagnetism by light irradiation or application of an electric field. 3. A magnetic recording medium according to claim 1 or 2, wherein a layer containing a magnetic material that exhibits ferromagnetism by irradiation with light and a recording holding layer are laminated. 4. A magnetic recording medium according to claim 1, wherein a layer containing a magnetic body that exhibits ferromagnetism by applying an electric field and a dielectric layer are laminated.