JPH03272453A - Evaluation of two-layer film medium - Google Patents

Abstract

PURPOSE:To evaluate the magnetic characteristics of a two-layer film medium easily by applying a magnetic field in four specific directions to measure magnetic torque quantities and calculating the magnetization and uniaxial magnetic anisotropy energy density of each layer using a specific calculation formula. CONSTITUTION:The magnetization reversal critical magnetic fields of the respective layers of a two-layer film medium having uniaxial magnetic anisotropy obtained when a magnetic field is applied to the respective layers of the two-layer film medium at an angle of 45 deg. to the magnetization easy axial direction of the respective layers are set to Hx,Hy(Hx<Hy) and a magnetic field H(H<Hy) is applied to the respective layers in four directions forming an angle 45 deg. with respect to the easy axial direction of the respective layers to measure magnetic torque quantities. The magnetic torque quantities of respective axes are determined like formula V and magnetic torque quantities in such a case that the respective layers are set to single layer films are added at every layers according to formulae I, II to calculate values Lx'Ly. Next, the magnetization Mi (i=x,y) and uniaxial magnetic anisotropy energy density Ki (i=x,y) and uniaxial magnetic anisotropy energy density Ki (i=x,y) of each of the layers are calculated according to formulae III, IV [wherein Vi (i=x,y) is the volume of each layer and a and b are the intercepts of the inclinations of graphs of (Li/H)<2> and H<2> and (Li/H)<2>]. By this method, the magnetic characteristics of the two-layer film medium can be easily evaluated.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for evaluating a two-layer film medium, and in particular to determining the magnetization and uniaxial magnetic anisotropy energy density of each layer of Ly by measuring magnetic torque. The present invention relates to a method for evaluating a two-layer film medium characterized by the following.

(Prior Art) In recent years, research has been actively conducted on two-layer media in which a perpendicular magnetization film and an in-plane magnetization film are combined as magneto-optical recording materials and perpendicular magnetic recording materials. Even a single-layer perpendicularly magnetized film has a two-layer structure with an in-plane magnetization component due to oxidation of the initial film formation layer or interface. Conventionally, methods for evaluating the magnetic anisotropy energy and magnetization of each film of these two-layer film media include a method of evaluating each single-layer film with a separate bottom film, and a method using ESR.

(Problems to be Solved by the Invention) However, in the conventional method, there was a problem in that the two-layer film medium could not be used as a sample as it was, and a sample had to be prepared separately. An object of the present invention is to provide an evaluation method that can easily evaluate the magnetic properties of each layer in a two-layer film state.

(Means for Solving the Problem) The present invention provides a magnetic field in a direction of 45 degrees with respect to the easy axis direction of each layer of a two-layer film medium having uniaxial magnetic anisotropy in the X-axis direction and the y-axis direction, which are orthogonal to each other. The critical magnetic fields for magnetization reversal when Hx and Hy (Hx<Hy) are applied, and among the four directions that are 45 degrees to the easy axis direction of each layer,
A magnetic field H (H < Hy) is applied in each direction, the amount of magnetic torque corresponding to the magnitude of the magnetic field H is measured, and the measured amount of magnetic torque is determined as follows, and the [1,1] axis is direction,
When 0<H<Hy -A[-1, 11 axial direction, 0
When <H<Hx -C[-1,1] axial direction, HX
When <H<Hy A[-1,-1] axial direction, 0<
When H<Hx, D[-1,-1] axial direction, Hx
When < H < Hy -B[1,-1] axial direction,
When O<H<Hy B From these magnetic torque amounts, use the following equations (1) and (2) to calculate the magnetic field in the easy axis direction of each layer at 45 degrees and 135 degrees when each layer is a single layer. Calculate the values LX and Ly by adding the amount of magnetic torque for each layer when applying , Lx=A+C=B+D
(1) L, =~A+B=C-D
(2) A two-layer film characterized in that the magnetization Mi (t = x, y) and uniaxial magnetic anisotropy energy density Ki (i = x, y) of each layer are determined by the following equations (3) and (4). This is a method for evaluating media.

Mi: (2bi)” / Vi
(3) KH=bi/(2aH-Vi)
(4) (However, Vi (i=x, y
) is the volume of each layer, and a and b are the slopes of the graphs of (Li/H)2 and H2 and the intercepts of the (Li/H)2 axis. ) Further, the magnetization Mi (i = x, y) and the uniaxial magnetic anisotropy energy density Ki (i = x, y) can be determined from the measured magnetic torque amount A to the measured magnetic torque amount A as follows. From the measured magnetic torque amount, the following equation (1) or (2) is used to calculate the easy axis direction of each layer and the 45
Find one of the values Lx or Ly, which is the sum of the magnetic torque amount for each layer when a magnetic field is applied in the 135° and 135° directions, and Lx=A+C=B+D (
1) L, = -A+B=C-D
(2) LX or Li determined by Ly using the following equations (3) and (4).

Find the magnetization Mi (i = x, y) and uniaxial magnetic anisotropy energy density Ki (i = x, y) of the layer corresponding to M
i: (2bi) 1/2Vi
(3) K;=bi/(2aH-Vi)
(4) (where V; (i=x, y) is the volume of each layer, a, b are the slope of the graph of (Ly/H)2 and H2 and the intercept of the (Li/H) two axes.

) The magnetic field dependence Lx45 or Ly45 of the magnetic torque measured when a magnetic field is applied in the direction of 45 degrees from the easy axis direction when each layer is made into a single layer film using the following equation (5) or (6). Find, LX45(H)=(Lx±(MyVyH)2/2KyV
y)/2 (5)Ly45(H)=(Ly±(
MxVxH)2/2KxVx)/2(6) (However, V
i (i=x, y) is the volume of each layer. ) Below (3)
Lx45 or Ly4 obtained by Ly using the formula and formula (7)
The magnetization Mi (i = x, y) and uniaxial magnetic anisotropy energy density KH (i = x, y) of the layer corresponding to No. 5 are determined.

Mi=-(2bi)"/Vi
(3) Ki = (bi / Vi) X 1/a
i (7) (where Vi (i=x, y) is the volume of each layer,
a, b are the slope of the graph of (Li/H)2 and H2 and (
Li/H) biaxial intercept. ) (Function) For the measurement, a method for measuring uniaxial magnetic anisotropy proposed by Miyajima et al. (Journal of Bride Physics, Vol. 4, 4669-46711976) was used. In this method, a magnetic field is applied in a direction of 45 degrees with respect to the easy axis, and the uniaxial anisotropy constant and magnetization are determined from the dependence of the magnetic torque amount on the magnetic field. In the case of a single-layer film, all 45-degree directions are equivalent, but if two mutually perpendicular uniaxial anisotropies coexist and the critical magnetic field for magnetization reversal of each layer is different, then in a specific external magnetic field range , the four directions (see FIG. 1) that form 45 degrees with the easy axis direction of the base membrane are no longer equivalent. The magnetic field dependence of the magnetic torque in at least two non-equivalent directions that are 45 degrees to the easy axis of the base film is measured, and the magnetic field dependence of the magnetic torque of each layer is separated by the sum and difference of these, and the magnetic difference of the base film is determined. Find orientation and magnetism.

(Example) As an example of a case where the two precepts are perpendicular to each other, implementation is performed on a pseudo-composite two-layer film of a perpendicular film (magneto-optical recording film) with a large coercive force and an in-plane film (Ni wire) with a small coercive force. Give an example.

The in-plane direction is the X direction, the perpendicular direction is the y direction, and when a magnetic field is applied at 45 degrees to the easy magnetization direction, the critical magnetic field for magnetization reversal of the in-plane film and perpendicular film is Hx, Hy (Hx < Hy). . The in-plane and perpendicular magnetization directions when the in-plane film and the perpendicular film are made into single-layer films, and the magnetic field dependence of the magnetic torque amount when the magnetic field H is applied in the directions of 45 degrees and 135 degrees, respectively, are expressed as LX.
45(H), LX135(H).

L, 45 (H), L, 135 (H). In the initial state, the magnetization is oriented in the direction of the x- and y-axis strain, and if the clockwise magnetic torque is positive, the magnetic torque shown in Table 1 is observed depending on the direction of magnetic field application and the applied magnetic field region. here,
A = LX45(H) -Ly45(H), B =
LX45(H) +Lyxas(H), C"LX135
(H) + Ly45(H), D = LX135(H
) -Lyxa5(H).

This is LyLx Power Component Table 1. For A+C or B+D, LyLx45(H)+Lx135(HX=Lx) or Lx45(H)+Lx135(HX=Lx)
Similarly to y, from −A+B and CD, L3=45(H) +
Lyta5 (HX = Ly) also stops. A, B, C, and D used for calculation use the same magnetic field region. Miyajima et al.'s method calculates from L45(H), but the method of the present invention calculates 2Lx(H) = LX45 + LX135
(H), or 2L, (H) = Ly45 + Ly
14 (i=x or y) represented by 135(H). In the following, for simplicity, it will be written as 14(H)=LH. In order to determine the uniaxial anisotropy and magnetization from the magnetic field dependence of Li, only the second-order term is considered in calculation as the uniaxial magnetic anisotropy energy. Then, the relationship between Li and H is (Li/H)2=((MiVi)4/16(Ki
It is expressed as Vi)2)H2+ (MiVi)2/2 (8). Here, i represents each layer of the two-layer structure film. Here, i=x corresponds to the in-plane magnetization layer, and i=y corresponds to the perpendicular magnetization layer. Therefore, (Li/H)2 and H2
The slope ai and the y-axis intercept bi of the graph of Ly are the magnetization M of each layer.
i and the uniaxial magnetic anisotropy energy density Ki is Mi:
(2bi)” / Vi (
3) Ki=bi/(2ai・V,)
It also stops as (4). Vi is the volume of the layer of interest.

From Table 1, it can be seen that Q < H < Hz can be used to calculate LyLx, and o < H < Hy can be used to calculate L. In the case of the y component, since H7 is large,
From the region of Hx<H<Hy, the Ly component was separated by -A+B, and the magnetic anisotropy energy 9 and magnetization M were determined from equations 8), (3), and (4). Next, in the case of the Lx component, as the in-plane anisotropy of the Area is not available. Therefore, the anisotropy and magnetization of the soft magnetic component were determined using LyA+B in the region Hx<H<Hy. In this case, A+B=2Lx45(H) (Ly45(H)-L
yta5(H)). From calculation IL/45 (H)
L, y135(H)l=(M,V,H)2/2KyV
, and Ly This value is obtained from equations (3) and (4). Further, as in this case, when the torque amount of LX45(H) is large and the anisotropy of the y component is large and the magnetization is small, it can be ignored. Therefore, the magnetic anisotropy and magnetization of xIfi were determined from Lx45(H) by the method of Miyajima et al. Table 2 shows the components of the two-layer film thus determined and the results of measurements for each single-layer film. It can be seen that the results for the composite membrane are in good agreement with the results for the single layer membrane.

Table 2 Magnetic anisotropy and magnetization of each layer (effects of the invention) This measurement method can be applied to two-layer films with mutually perpendicular uniaxial anisotropy, and can easily measure the magnetic anisotropy constant and magnetization of each layer. can be evaluated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the easy axis direction of each layer and the applied magnetic field direction.

Claims (2)

[Claims] (1) Each magnetization reversal criticality when a magnetic field is applied in a direction of 45 degrees to the easy axis direction of each layer of a two-layer film medium having uniaxial magnetic anisotropy in the mutually orthogonal x-axis direction and y-axis direction. The magnetic fields are H_x, H_y (H_x<H_y), and the magnetic field H (H<H_y) is applied in each of the four directions forming a 45 degree direction with respect to the easy magnetization axis direction of each layer, and the magnitude of the magnetic field H is Measure the amount of magnetic torque corresponding to
Axial direction, when 0<H<H_y -A[-1, 1] axial direction, when 0<H<H_x -C[-1, 1] axial direction, H_
When x<H<H_y, A[-1, -1] axis direction, 0<H
When <H_x, D[-1, -1] axis direction, H_x<H<
When H_y -B[1, -1] axial direction, 0<H<H_y
When B From these magnetic torque amounts, the following (1), (2
), calculate the average values L_x and L_y of the magnetic torque amount for each layer when a magnetic field is applied in directions of 45 degrees and 135 degrees with respect to the easy axis direction of each layer when each layer is a single layer film, L_x= A+C=B+D (1) L_y=-A+B=C-D (2) Magnetization M_i (i=x
, y) and uniaxial magnetic anisotropy energy density K_i (i=
1. A method for evaluating a two-layer film medium, characterized by determining the values (x, y). M_i=(2b_i)^1^/^2/V_i(3) K_i=b_i/(2a_i^1^/^2・V_i)(
4) (However, V_i (i=x, y) is the volume of each layer, a, b
is the slope of the graph of (L_i/H)^2 and H^2 and (L_
i/H)^ It is an intercept of two axes. ) (2) Each magnetization reversal when a magnetic field is applied in a direction of 45 degrees to the easy magnetization axis direction of each layer of a two-layer film medium having uniaxial magnetic anisotropy in the mutually orthogonal x-axis direction and y-axis direction. Let the critical magnetic field be H_x, H_y (H_x<H_y),
A magnetic field H (H<H_y) is applied in each of the four directions that are oriented at 45 degrees with respect to the easy axis direction of each layer, and the amount of magnetic torque corresponding to the magnitude of the magnetic field H is measured. The magnetic torque amount is determined as follows, [1, 1]
Axial direction, when 0<H<H_y -A[-1, 1] axial direction, when 0<H<H_x -C[-1, 1] axial direction, H_
When x<H<H_y, A[-1, -1] axis direction, 0<H
When <H_x, D[-1, -1] axis direction, H_x<H<
When H_y -B[1, -1] axial direction, 0<H<H_y
When B From these magnetic torque amounts, use the following equation (1) or (2) to calculate the magnetic field when applying a magnetic field in the easy axis direction of each layer, 45 degrees and 135 degrees when each layer is a single layer film. Find either L_x or L_y, which is the average value of the magnetic torque amount for each layer, L_x=A+C=B+D (1) L_y=-A+B=C-D (2) According to the following equations (3) and (4), Magnetization M_i (i=x, y) and uniaxial magnetic anisotropy energy density K_i (i=x, y) of the layer corresponding to the determined L_x or L_y
Find M_i=(2b_i)^1^/^2V_i(3) K_i=b_i/(2a_i^1^/^2・V_i)(
4) (However, V_i (i=x, y) is the volume of each layer, a, b
is the slope of the graph of (L_i/H)^2 and H^2 and (Li
/H)^ It is an intercept of two axes. ) The following equation (5) or (
6) Magnetic field dependence of magnetic torque measured when each layer is a single layer film and a magnetic field is applied in a direction of 45 degrees from the easy magnetization axis direction L_x_4_5 or L_y_4_5
Find L_x_4_5(H)=(L_x±(M_yV_yH)
^2/2K_yV_y)/2(5) L_y_4_5(H)=(L_y±(M_xV_xH)
^2/2K_xV_x)/2(6) (However, V_i (i = x, y) is the volume of each layer.) L_x obtained from the following equations (3) and (7)
Magnetization M_ of the layer corresponding to _4_5 or L_y_4_5
1. A method for evaluating a two-layer film medium, comprising determining i (i=x, y) and uniaxial magnetic anisotropy energy density K_i (i=x, y). M_i=(2b_i)^1^/^2/V_i(3) K_i=(b_i/V_i)×1/a_i(7) (However, V_i(i=x, y) is the volume of each layer, a, b
is the slope of the graph of (L_i/H)^2 and H^2 and (L_
i/H)^ It is an intercept of two axes. )