JP2795688B2 - Perpendicular magnetization film - Google Patents

Description

The present invention relates to an oxide perpendicular magnetization film having perpendicular magnetization anisotropy and used for perpendicular magnetic recording, a magneto-optical recording medium and the like.

(Prior Art) Perpendicular magnetic recording and magneto-optical recording are being studied as new magnetic recording methods capable of high-density recording. It is necessary to use a perpendicular magnetization film having magnetic anisotropy in the direction perpendicular to the film as a medium used in these recording methods.

Japanese Patent Application Laid-Open No. 61-111511 discloses a perpendicular ferrite film in which the saturation magnetization Ms is reduced by replacing a part of Co or Fe of cobalt ferrite with a non-magnetic atom such as Mn or Al. ing. Further, in the case of a magneto-optical recording medium, a cobalt ferrite spinel thin film having acid resistance and a large magneto-optical effect, which is different from a conventional rare earth-transition metal system, has been reported.

(Problems to be Solved by the Invention) However, since cobalt ferrite is originally an isotropic material, Ku⊥ ≧ 2πMs ² (Ku⊥ is a perpendicular anisotropy constant, Ms is a saturation magnetization), or Hc⊥> Hc (Hc⊥ the vertical coercive force, Hc in-plane direction of the coercive force), SQ⊥> SQ (SQ⊥ the vertical squareness ratio = B _r / B _m, SQ is the in-plane direction squareness ratio)
And it is difficult to obtain a perpendicular magnetization film.

An object of the present invention is to provide a perpendicular magnetization film having good perpendicular magnetic anisotropy in view of the above-mentioned problems of the related art.

(Means for Achieving the Object) In order to achieve the above object, the perpendicular magnetization film of the present invention comprises:
Co _x Fe _3-xy Cu _y O ₄ and the range of values of x and y 0.5 ≦
It is characterized by x ≦ 2.0 and 0 <y <0.4.

(Action) By the above composition, that is, Co or Fe
Is replaced by Cu, Hc⊥ / Hc and SQ⊥ / SQ are improved, and the perpendicularity of the film is improved.

If the value of y as the Cu substitution amount is not less than 0.4, the Faraday rotation angle becomes small. The reason for setting the amount of x, which is the amount of Co, to the above-described range is that if the amount is out of this range, the Faraday rotation angle also becomes small.

(Example) As an example, a Cu-substituted Co ferrite perpendicular magnetization film represented by Co _1.2 Fe _1.6 Cu _0.2 O ₄ will be described as an example.

[Create target]

Powders of CoO, Fe ₂ O ₃ , and CuO were prepared so as to have a desired composition, pulverized by a ball mill for 20 hours, and then calcined at 800 ° C. for 3 hours in the air.

After calcining, the mixture was ground again with a ball mill for 20 hours, dried, kneaded with polyvinyl alcohol as a binder, and press-molded.

After molding, heat treatment in air at 1050 ° C for 3 hours to obtain a disc-shaped sintered body of polycrystalline Co ferrite with a diameter of about 10cm.
This sintered body was bonded to a Cu backing plate to obtain a target.

(Deposition)

Corning 7059, a glass substrate manufactured by Corning, was attached to the high frequency sputtering device, and the inside of the device was 6.5 × 10 ^-5 P
After evacuation to a, Ar gas was introduced into the apparatus until the pressure became about 7 Pa.

Thereafter, a predetermined high-frequency voltage is applied between the substrate and the target to start glow discharge, and the Ar ⁺
Sputter the target surface with Co _1.2 Fe on the substrate
_1.6 Cu _0.2 O ₄ film was prepared. At this time, the substrate temperature was set to 300 ° C., the input power was set to 2.2 W / cm ^2, and sputtering was performed for a predetermined time so that the film thickness became 0.5 μm.

This film was heat-treated together with a glass substrate at 600 ° C. for 3 hours in air to promote crystallization.

(Film evaluation)

As a result of examining the crystallinity of the formed film by X-ray diffraction, it was found that the polycrystal had a strong peak in the (311) direction both after film formation and after heat treatment.

As a result of measuring the magnetization characteristics in the in-plane () and perpendicular (⊥) directions with a vibrating magnetometer (VSM), the force in the perpendicular direction has a large coercive force Hc and a large squareness ratio SQ. It can be seen that it is.

FIG. 1 is a BH hysteresis loop of this film,
⊥ indicates a vertical direction, and indicates an in-plane direction. For comparison, Co _1.4 F, which is a Co ferrite not substituted with Cu, is used.
The BH hysteresis loop of e _1.6 O ₄ is shown in FIG. As can be seen from FIG. 1, the one partially replaced by Cu has both Hc and SQ greater in the vertical direction than in the in-plane direction, has good loop squareness, and is a perpendicular magnetization film. on the other hand,
In FIG. 2, the material replaced with Cu has almost the same Hc and SQ in the vertical direction and the in-plane direction, has poor squareness of the loop, and is not a perpendicular magnetization film.

Similarly, Co ferrite partially substituted by Cu of the above composition,
FIG. 3 shows the results of measuring the Faraday loop at a wavelength of 630 nm of Co ferrite not replaced by Cu, respectively.
As shown in FIG. As can be seen from the comparison between FIG. 3 and FIG. 4, the squareness ratio (θ _Fr /
θ _FS ) is large and can be used as a magneto-optical recording medium.

[Relationship between Cu substitution amount and properties] Co _1.6 Fe _1.4 O ₄ is used as a reference composition, and a part of Co is
For Co _1.6-x Fe _1.4 Cu _x O ₄ substituted with Cu, the substitution amount x
By changing the coercive force Hc⊥ in the vertical direction, the saturation magnetization Ms, the Faraday rotation angle θ _F , and the ratio Hc⊥ / H between the coercive force in the vertical direction and the in-plane direction.
c, Squareness ratio SQ⊥ / SQ, Faraday loop squareness ratio θ _Fr
/ θ _FS was measured and calculated. The Faraday rotation angle is wavelength 6
Measured at 30 nm. Table 1 shows the results. Table 1
In the bottom line (Sample No. 6), not Co but part of Fe
An example of substitution with u is also shown.

As can be seen from Table 1, in the range of x = 0.05 to 0.35, Hc⊥ / Hc, SQ⊥SQ, θ _Fr / θ _FS are all improved,
In particular, it can be seen that the improvement of Hc⊥ / Hc is remarkable. Fe to C
Good values are also obtained when u is replaced.

For Co _1.6-x Fe _1.4 Mn _x O _{4 in} which part of Co was replaced with Mn, the Hc⊥ / Hc and SQ⊥ / SQ when the amount of substitution x was changed.
In addition, the change in the squareness ratio θ _Fr / θ _FS of the _Faraday loop is examined, and the results are shown in FIGS. 5, 6 and 7, respectively, in comparison with the case where the Cu is substituted. As can be seen from FIGS. 5 to 7, in the case of Mn substitution, the magnetization direction is superior in the in-plane direction, whereas in the case of Cu substitution, the perpendicular magnetization characteristics can be improved with a small amount of substitution. 5 and 6, it can be seen from FIG. 5 and FIG. 6 that the larger the substitution amount is, the larger Hc⊥Hc in the range where the substitution amount x is up to 0.2.
, SQ⊥ / SQ is improved and becomes almost constant in the range of 0.2 to 0.4. Also, as can be seen from FIG.
The value of _Fr / θ _FS is 0.9 or more when the substitution amount x is 0.2 or more,
It can be seen that application to a magneto-optical recording medium becomes possible.

Further, Table 2 shows that the composition of Co _1.2 Fe _1.8 O ₄ and the case where the Cu substitution amount for Fe was changed in this composition (Sample No.
= 7 to 10), and the amount of Fe was adjusted to 1.8
When the substitution amount of Cu for Co was changed to about
= 11, 12). As can be seen from Table 2,
Hc⊥ / Hc, SQ⊥ / SQ, etc. were improved by the Cu substitution, but when the Cu substitution amount became 0.5 as in sample No. 10, θ _F and S
Q⊥ / SQ tends to decrease.

Table 3 shows that the composition of Co _1.7 Fe _1.3 O ₄ and the case where the Cu substitution amount of Fe was changed in this composition (Sample No.
= 13 to 16). As in the case of sample No. 14, when the Cu substitution amount is 0.05 or more, Hc⊥ / Hc and SQ⊥ / SQ are improved.

Tables 4 and 5 are shown for comparison with the present invention.
This shows an example in which Mn or Al is substituted for Co or Fe, and in each case, Hc⊥ / H
c, SQ⊥ / SQ is flat or decreasing.

In the above embodiment, the film was formed by the sputtering method, but the vacuum evaporation method, the ion plating method, and the plasma CV method were used.
Similar effects can be obtained by a thin film forming technique such as the D method.

(Effects of the Invention) According to the present invention, the coercive force ratio Hc⊥ / Hc and the squareness ratio S
Q⊥ / SQ is improved, and a cobalt ferrite film having good perpendicular magnetic anisotropy can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a BH hysteresis loop diagram of a film having a composition according to one embodiment of the present invention, FIG. 2 is a BH hysteresis loop diagram of a conventional ferrite, and FIG. FIG. 4 is a Faraday loop diagram of a film of a conventional ferrite, and FIGS. 5, 6, and 7 are Cu diagrams.
Ratio of coercive force to substitution amount and Mn substitution amount Hc⊥ / Hc
Is a diagram illustrating a change in the value of the squareness ratio theta _Fr / theta _FS squareness ratio SQ⊥ / SQ and the Faraday loop.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-165447 (JP, A) JP-A-63-104313 (JP, A) JP-A-63-1010 (JP, A) JP-A-60-160 261051 (JP, A) JP-A-60-150248 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01F 10/20

Claims (1)

(57) [Claims] 1. A Co _x Fe indicated by _3-xy Cu _y O _4, and x, perpendicular magnetization film, wherein the range of values of y is 0.5 ≦ x ≦ 2.0,0 <y < 0.4.