JP5738791B2 - 3D magnetic recording media - Google Patents

Description

  Embodiments described herein relate generally to a three-dimensional magnetic recording medium.

  In recent years, a three-dimensional magnetic recording medium corresponding to a three-dimensional magnetic recording method has been proposed in order to further improve the recording density of magnetic recording products such as a hard disk drive (HDD). A three-dimensional magnetic recording medium is a recording medium having a plurality of recording layers for recording data. The three-dimensional magnetic recording medium has a higher recording density per unit area of the medium than the single-layer recording medium having only one recording layer according to the number of recording layers.

JP 2009-80904 A

  However, in the above-described three-dimensional magnetic recording method, writing is performed on each recording layer with the same bit size, and the recording densities of the plurality of recording layers are all the same. When the recording layer is made multi-layered, it is necessary to differentiate the effective magnetic anisotropy in each recording layer, and therefore the limit recording density of the recording layer changes according to the degree of the effective magnetic anisotropy. Therefore, when the recording density is the same for all recording layers, the recording density cannot be increased beyond the recording density of the recording layer having the lowest limit recording density (the bit is large). Recording layers are recorded in a large number, resulting in poor recording efficiency.

  The present disclosure has been made in order to solve the above-described problem, and an object thereof is to provide a three-dimensional magnetic recording medium capable of increasing recording efficiency.

  The three-dimensional magnetic recording medium according to the present embodiment includes a plurality of recording layers and a plurality of intermediate layers. The plurality of recording layers are made of a magnetic material. The plurality of intermediate layers are formed of a nonmagnetic material. The recording layer has an effective magnetic anisotropy of the recording layer from a recording layer located far from the magnetic head used for data recording and data reading toward a recording layer located near the magnetic head. The recording layers are stacked so that the degree becomes higher sequentially. The higher the degree of the effective magnetic anisotropy, the higher the recording density of the recording layer. The recording layer and the intermediate layer are alternately stacked.

The figure which shows the three-dimensional magnetic recording medium concerning this embodiment. The figure which shows the bit pattern of the three-dimensional magnetic recording bit patterned media (BPM) medium corresponding to a perpendicular magnetic recording system. The figure which shows the bit pattern of the three-dimensional magnetic recording continuous medium corresponding to a perpendicular magnetic recording system. The figure which shows an example in the case of writing data in a three-dimensional magnetic recording medium. The figure which shows an example in the case of reading data from a three-dimensional magnetic recording medium. The figure which shows the bit pattern of the three-dimensional magnetic recording BPM medium corresponding to an in-plane magnetic recording system. The figure which shows the bit pattern of the three-dimensional magnetic recording continuous medium corresponding to an in-plane magnetic recording system. The figure which shows an example of the BPM medium which has a recording layer which couple | bonded multiple magnetic layers. The figure which shows an example of the continuous medium which has a recording layer which couple | bonded multiple magnetic layers. The figure which shows the example of preparation of the three-dimensional magnetic recording medium which concerns on this embodiment.

  In a conventional magnetic recording medium, binary “1” and “0” are recorded as the magnetization direction of a minute region called “bit”. Data is written to the magnetic recording medium by applying a writing magnetic field larger than the coercive force of the magnetic recording medium from the magnetic head to the bit and reversing the magnetization direction of the bit. When reading data, the magnetic head detects the leakage magnetic field from the bit, whereby the direction of magnetization of the bit can be determined.

In general, an increase in magnetic recording density means a reduction in bit size. In order to maintain a sufficient read signal-to-noise ratio (SN ratio) when the size of one bit is reduced, it is necessary to refine the magnetic crystal grains of the magnetic recording medium. With the miniaturization of magnetic crystal particles, the thermal stability of the magnetic crystal particles becomes a problem. The thermal stability of the magnetic crystal grains is K _eff V / k _B T (K _eff , V, k _B and T represent the effective magnetic anisotropic energy density, volume, Boltzmann constant and temperature of the magnetic crystal grains, respectively). expressed. If sufficient thermal stability is not achieved, the direction of magnetization may be reversed due to thermal fluctuations even at room temperature, and recorded data may be lost. Therefore, there is a limit to reducing the bit size. In the conventional single-layer magnetic recording medium, when the recording density is about Tbit / in ² , it is difficult to further reduce the bit size.

Hereinafter, the three-dimensional magnetic recording medium according to the present embodiment will be described in detail with reference to the drawings. Note that, in the following embodiments, the same reference numerals are assigned to the same operations, and duplicate descriptions are omitted as appropriate.
A three-dimensional magnetic recording medium according to this embodiment will be described with reference to FIG.
A three-dimensional magnetic recording medium 100 according to the present embodiment includes a plurality of recording layers 101 and a plurality of nonmagnetic intermediate layers 102. In the three-dimensional magnetic recording medium 100 according to the present embodiment, a plurality of recording layers 101 are multilayered. In the example of FIG. 1, the recording layer 101 is stacked in n layers (n is a natural number of 2 or more). As shown in FIG. 1, magnetic layers 101 and nonmagnetic layers 102 are alternately stacked one by one.

The recording layer 101 is made of a magnetic material, and records data by changing the direction of magnetization of the magnetic material. The recording layer 101 preferably has a magnetic anisotropy energy density of about 10 ⁶ erg / cm ³ in order to achieve a magnetic recording density of Tbit / in ² or higher. Therefore, as the magnetic material forming the recording layer 101, for example, an alloy containing Co and Pt as main components, an alloy containing Fe and Pt as main components, an alloy containing Co, Fe and Pt as main components, Co It is desirable to use an alloy containing Cr and Pt as main components, an alloy containing Fe and Pd as main components, or a Co / Pt multilayer film or a Co / Pd multilayer film.

  Further, as the thickness of the recording layer 101 increases, the thickness of the three-dimensional magnetic recording medium 100 increases, so that the strength of the magnetic field from the magnetic head applied to the recording layer 101 far from the magnetic head decreases. For this reason, it is necessary to reduce the degree of coercive force and effective magnetic anisotropy of the recording layer located far from the magnetic head, and the limit recording density is lowered. Accordingly, the thickness of the recording layer 101 is preferably thin. However, if the thickness is too thin, the thermal stability is deteriorated due to a decrease in volume. Therefore, the thickness of each recording layer is preferably about 3 nm to 10 nm. The degree of effective magnetic anisotropy may be measured using, for example, a sample vibration type magnetometer (VSM) or a torque magnetometer (Torque Magnetometer).

The recording layer is laminated so that the degree of effective magnetic anisotropy of the recording layer 101 increases from the recording layer 101 located far from the magnetic head toward the recording layer 101 located near the magnetic head. The higher the degree of effective magnetic anisotropy, the higher the recording density.
The nonmagnetic intermediate layer 102 is formed of, for example, a nonmagnetic material such as Ti or Cr, and is laminated between the recording layers 101. The nonmagnetic intermediate layer 102 serves to isolate the upper and lower recording layers 101 and to control the crystal orientation of the recording layers. The nonmagnetic material forming the nonmagnetic intermediate layer 102 is preferably close to the recording layer material and the crystal lattice constant. If the nonmagnetic intermediate layer 102 is too thick, the recording density of the recording layer far from the head is lowered as described above. On the other hand, if the nonmagnetic intermediate layer 102 is too thin, a sufficient isolation effect cannot be obtained. Therefore, the thickness of the nonmagnetic intermediate layer 102 is preferably 1 nm to 5 nm.

In three-dimensional magnetic recording, the recording layer is selected according to the magnetic resonance frequency, and writing and reading are performed. Therefore, it is necessary to differentiate the magnetic resonance frequency of each recording layer. For example, in the case of perpendicular magnetic recording, the magnetic resonance frequency of the recording layer is expressed by equation (1).

Here, γ is a magnetic rotation ratio, and H _k ^eff is an effective magnetic anisotropy magnetic field. As can be seen from the equation (1), as the effective magnetic anisotropic magnetic field H _k ^eff of the recording layer increases, the magnetic resonance frequency f also increases. Therefore, when recording layers having different effective magnetic anisotropy magnetic fields are laminated, it is possible to perform writing and reading with respect to a desired recording layer using a magnetic resonance frequency unique to each recording layer.

Further, the maximum recording density at which data can be written to the recording layer (hereinafter referred to as the limit recording density) is determined by the effective magnetic anisotropy of the magnetic material of the recording layer. This is because the bit of the recording layer requires higher effective magnetic anisotropy in order to maintain thermal stability as the bit size is smaller. Therefore, the recording layer with higher effective magnetic anisotropy can set the recording density of writing to the limit recording density.
Note that the greater the degree of effective magnetic anisotropy, the greater the retention of each recording layer, and the greater the magnetic field required for writing. On the other hand, the magnetic field generated from the magnetic head becomes weaker as the distance from the magnetic head increases. Accordingly, it is desirable that a recording layer having a low coercive force, that is, a low degree of effective magnetic anisotropy, is laminated on the lower layer of the three-dimensional magnetic recording medium. Therefore, as shown in FIG. 1, the lowermost recording layer of the three-dimensional magnetic recording medium 100 has the lowest degree of effective magnetic anisotropy and the magnetic resonance frequency is also low. On the other hand, the uppermost recording layer of the three-dimensional magnetic recording medium has the highest degree of effective magnetic anisotropy and the magnetic resonance frequency is also high.

Next, an example of the bit pattern of the three-dimensional magnetic recording medium according to the present embodiment will be described with reference to FIGS.
The bit pattern shown in FIG. 2 shows an example of a bit patterned medium (BPM) medium in which adjacent recording bits 201 are separated by a nonmagnetic material 202. FIG. 3 shows an example of a continuous medium in which recording bits 301 are adjacent to each other, not a bit patterned medium.
2 and 3, it can be seen that the lower recording layer 101 has a larger bit size, and the upper recording layer 101 has a smaller bit size and a higher recording density.

Next, an example of writing data to the three-dimensional magnetic recording medium 100 according to the present embodiment will be described with reference to FIG.
The example shown in FIG. 4 shows a case where data is recorded on the lowermost recording layer 101.
The magnetic head 401 applies a high frequency magnetic field 402 at the same frequency as the magnetic resonance frequency of the lowermost recording layer 101. The lowermost recording layer 101 to which the high-frequency magnetic field 402 is applied is in a magnetic resonance state. The magnetic head 401 generates a write magnetic field 403 separately from the high frequency magnetic field 402. If the recording layer 101 is in a magnetic resonance state, magnetization reversal occurs even if the applied magnetic field is less than the coercive force. Therefore, data is written to the desired recording layer by adjusting the frequency of the high-frequency magnetic field 402 from the magnetic head 401. be able to.

Next, an example of reading data from the three-dimensional magnetic recording medium 100 according to the present embodiment will be described with reference to FIG.
The example shown in FIG. 5 shows a case where data is read from the lowermost recording layer 101.
A high frequency magnetic field 501 is applied from the magnetic head 401 in accordance with the magnetic resonance frequency of the recording layer to be read, and the lowermost recording layer 101 is brought into a magnetic resonance state. Further, the magnetic head 401 applies a read magnetic field 502 to the lowermost recording layer 101. Since the energy absorption by the high-frequency magnetic field 501 changes depending on the magnetization direction of the bit of the recording layer in the magnetic resonance state, the magnetic head 401 detects the change in energy absorption, thereby reading the data by determining the magnetization direction. Can do.

  Next, another example of the recording layer of the three-dimensional magnetic recording medium 100 will be described with reference to FIGS.

  6 and 7 show the case of the in-plane magnetic recording system in which the magnetization of the recording layer is in the in-plane direction, not the perpendicular magnetic recording system. Further, the recording layer 601 shown in FIG. 6 shows the case of BPM in which the nonmagnetic material 202 is inserted between the bits 201, and the recording layer 701 shown in FIG. 7 does not have the nonmagnetic material 202 inserted between the bits 201. Show the case. Even in such a three-dimensional magnetic recording medium in which the recording layer of the in-plane magnetic recording system is multilayered, the degree of effective magnetic anisotropy of the recording layer is high as in the above-described three-dimensional magnetic recording medium of the perpendicular magnetic recording system. The same effect can be obtained by increasing the recording density.

  Further, a recording layer in which two or more magnetic layers are magnetically coupled may be used. FIGS. 8 and 9 show a case where a recording layer is formed by combining two magnetic layers. By combining two magnetic layers, there is an effect that the magnetization reversal of the recording layer is facilitated.

  FIG. 8 shows the case of a three-dimensional magnetic recording medium on which a recording layer 801 of the BPM method is laminated, and FIG. 9 shows the case of a three-dimensional magnetic recording medium on which a recording layer 901 not of the BPM method is laminated. In each recording layer 801 and recording layer 901, the write auxiliary layer 802 is laminated on the above-described recording layer 101, and the two layers together form one recording layer. In the three-dimensional magnetic recording medium shown in FIGS. 8 and 9, the recording efficiency can be increased by increasing the recording density as the effective magnetic anisotropy of the recording layer is higher. The write assist layer 802 can be formed using a material that easily reverses magnetization, such as NiFe or FeSi.

  Hereinafter, an example of manufacturing a BPM type three-dimensional magnetic recording medium according to the present embodiment will be described with reference to FIG.

  FIG. 10 is a diagram in which a part of the three-dimensional magnetic recording medium is cut out. The three-dimensional magnetic recording medium 1000 has three recording layers 101, and a laminated film including a magnetic layer formed on a glass substrate by sputtering ultrahigh vacuum film formation uses electron beam lithography and ion milling. Generated. The magnetic dots (bits) 201 of each recording layer are partitioned for each bit by a nonmagnetic material 202.

  In this embodiment, the recording layer 101 is generated using an FePtCu alloy or an FePt alloy. When the FePtCu alloy is used, if the Cu component is within 15 percent, the higher the Cu concentration, the higher the magnetocrystalline anisotropy and the higher the magnetic anisotropy magnetic field.

  Further, an alloy containing FePt as a main component has a large degree of magnetic anisotropy and a large damping constant. Therefore, the line width of magnetic resonance is as wide as several GHz. Therefore, in order to bring only the selected recording layer into a magnetic resonance state, it is desirable that the difference in magnetic resonance frequency between the recording layers is about 3 GHz to 5 GHz. In the following examples, the difference in magnetic resonance frequency between the recording layers is set to 5 GHz.

The uppermost recording layer (hereinafter referred to as the first recording layer 1001) closest to the magnetic head uses (FePt) ₉₀ Cu ₁₀ . In this composition, the effective magnetic anisotropy energy density is 3.5 × 10 ⁶ erg / cm ³ and the effective magnetic anisotropy magnetic field is 7 kOe. Here, in order to maintain sufficient thermal stability, it is necessary that K _eff V / k _B T> 60. Therefore, the volume of the magnetic dots needs to be 720 nm ³ or more. If the thickness of the recording layer is 5 nm and the interval between dots that can be finely processed is 12 nm, the in-plane magnetic dot size cannot be made smaller than 12 nm × 12 nm. Therefore, here, in order to realize the limiting density, the size of the magnetic dots in the plane of the first recording layer 1001 is set to 12 nm × 12 nm. At this size, the recording density is 1.12 Tbit / in ² . Therefore, based on the effective magnetic anisotropic magnetic field, the magnetic resonance frequency f ₁ of the first recording layer 1001 is about 20 GHz.

Intermediate recording layer (hereinafter, referred to as a second recording layer 1002), since the magnetic resonance frequency is about 5GHz smaller than the magnetic resonance frequency of the first recording layer 1001, it is necessary to the magnetic resonance frequency _{f 2} to about 15GHz is there. Therefore, (FePt) ₉₅ Cu ₅ is used as a material for forming the second recording layer 1002. (FePt) ₉₅ Cu _{5 has} an effective magnetic anisotropy energy density of about 2.5 × 10 ⁶ erg / cm ³ and an effective magnetic anisotropy magnetic field of about 5.3 kOe. Since the magnetic resonance frequency is 15 GHz, the size of the in-plane magnetic dot that satisfies the above-described equation of K _eff V / k _B T> 60 and maintains sufficient thermal stability is 12 nm × 17 nm or more. There is a need to. Therefore, the size of the magnetic dots in the plane of the second recording layer 1002 is 12 nm × 17 nm. With this size, the recording density is 0.93 Tbit / in ² .

Lowermost recording layer (hereinafter, a third that recording layer 1003), in order to approximately 5GHz smaller than the magnetic resonance frequency of the second recording layer 1002, it is necessary to set the magnetic resonance frequency _{f 3} to about 10 GHz. Therefore, the magnetic resonance frequency _{f 3} is set to approximately 10GHz, the effective anisotropy field of the third recording layer 1003 may be about 3.6KOe. Here, an FePt alloy is used. FePt has an effective magnetic anisotropy energy density of about 1.8 × 10 ⁶ erg / cm ³ and an effective magnetic anisotropy field of about 3.5 kOe. The size of the in-plane magnetic dots for maintaining sufficient thermal stability needs to be 12 nm × 23 nm or more. Therefore, here, the size of the magnetic dots in the plane of the third recording layer 1003 is 12 nm × 23 nm. With this size, the recording density is 0.93 Tbit / in ² .

As described above, if recording layers having different effective magnetic anisotropies are stacked and the sizes of the magnetic dots are designed to be 12 nm × 12 nm, 12 nm × 17 nm, and 12 nm × 23 nm, the limit recording density of each recording layer is These are 1.12 Tbit / in ² , 0.93 Tbit / in ² and 0.76 Tbit / in ² , respectively. Therefore, a three-dimensional magnetic recording medium having three recording layers has a total recording density of 2.81 Tbit / in ² .

When recording is performed on each recording layer at the same density as in a conventional three-dimensional magnetic recording medium, the total recording density of the entire medium is 2.28 Tbit / in ² , so that the three-dimensional structure of this embodiment is used. According to the magnetic recording medium, the recording density of the entire medium can be improved by about 23%.

  According to the three-dimensional magnetic recording medium according to the present embodiment described above, the recording layer closer to the magnetic head is laminated so that the effective magnetic anisotropy is higher, and the higher the effective magnetic anisotropy is, the higher the effective magnetic anisotropy is. By increasing the recording density, the recording efficiency can be increased.

  Note that the three-dimensional magnetic recording medium according to the present embodiment is assumed to be a disk-shaped disk such as an HDD (Hard Disk Drive), but is not limited to this, and may be a rectangle, square, polygon, or any other shape. It may be formed as long as the recording layer has a multilayer structure.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

100, 1000 ... three-dimensional magnetic recording medium, 101, 601, 701, 801, 901 ... recording layer, 102 ... nonmagnetic intermediate layer, 201, 301 ... recording bit, 202 ... non Magnetic body 401... Magnetic head 402 501 High frequency magnetic field 403 Writing magnetic field 502 Reading magnetic field 802 Writing auxiliary layer 1001 First recording layer 1002... Second recording layer, 1003... Third recording layer.

Claims (9)

A plurality of recording layers formed of a magnetic material;
A plurality of intermediate layers formed of a non-magnetic material,
The plurality of recording layers are arranged such that effective magnetic anisotropy of the recording layer is directed from a recording layer located far from a magnetic head used for data recording and data reading toward a recording layer located near the magnetic head. The recording density of the recording layer is set higher as the degree of effective magnetic anisotropy is higher.
A three-dimensional magnetic recording medium, wherein the recording layer and the intermediate layer are alternately laminated.   2. The three-dimensional magnetism according to claim 1, wherein the recording layer is laminated so that the recording density sequentially increases from a recording layer far from the magnetic head toward a recording layer close to the magnetic head. recoding media.   The three-dimensional magnetic recording medium according to claim 1, wherein data is recorded on the recording layer by using magnetic resonance.   4. The three-dimensional magnetic recording medium according to claim 1, wherein data is read from the recording layer by using magnetic resonance. 5.   The three-dimensional magnetic recording medium according to claim 1, wherein the recording layer has a magnetization direction in a thickness direction of the recording layer.   The three-dimensional magnetic recording medium according to any one of claims 1 to 4, wherein the recording layer has a magnetization direction in an in-plane direction of the recording layer.   The three-dimensional magnetism according to any one of claims 1 to 6, wherein the recording layer is formed by magnetically coupling two or more magnetic layers formed of a magnetic material. recoding media.   The tertiary according to any one of claims 1 to 7, wherein the recording layer includes a plurality of bits for recording the data, and the plurality of bits are magnetically separated. Original magnetic recording medium.   8. The recording layer according to any one of claims 1 to 7, wherein the recording layer includes a plurality of bits for recording the data, and the plurality of bits are not magnetically separated. Three-dimensional magnetic recording medium.

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