Evaluation of Anisotropic Film Structure of Amorphous Alloy by Computer Simulation
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paper, we will describe an anisotropic structure observed in the simulated film and discuss several views related to the magnetic anisotropy.
161 Mat. Res. Soc. Symp. Proc. Vol. 389 © 1995 Materials Research Society
n
0
Z
qrrq
S~~~Co atom
,,.
\Gd atom
•
L
.................
• Substrate z T
Atom
Fig. 1 Virtual space for the simulation.
Fig. 2 Schematic quenching condition.
PROCEDURE As the model for the growth of the amorphous thin film, a virtual RE-TM alloy film of Gd and Co was studied. The deposition composition of the alloy was chosen as Gd2nCosO. The deposition process was simulated with a molecular dynamics method. The Lennard-Jones potential is adopted as = 4{(U o(r)
-
1
(i=CoCo, GdGd, GdCo)
(1)
,where c is 0.167 X 10- J and a cc•c=0.25 X 10` m, q GdGd=0.36X 10-' m and C GdC. =0.31 X 10' m. A Lennard-Jones potential for interactions between deposited atoms was available to simulate the process of an amorphous Ar film discussed in our previous report.9 The simulation was performed in the virtual space as shown in Fig. 1. Here L and Lz were 58 A and 166 A, respectively. Periodic boundary conditions were adopted to xz and yz planes and a substrate was the bottom of xy planes. On the xy base plane, Co atoms were randomly set and the Co monolayer was used as a substrate. The Co atoms were distributed randomly to the z-axis direction and the standard deviation of the substrate atoms from a horizontal plane was defined as a , which means the magnitude of the roughness of the substrate surface. In order to introduce a thermal quench of the particles, the quenching radius r, was defined to all of atoms, as shown in Fig. 2. When there exists more than two atoms within the sphere of the radius rq, it is assumed that the thermal quench takes place and the energy of the remarked particle is taken out from the physical system. This process means that the energy of deposited atoms escapes through the substrate and an adhesion constant of the deposited atom in the growth process is almost one. The values of the rq, which may correspond to a quenching speed in a realistic process, were chosen as the distances of the Lennard-Jones potential minimum of 2.85 A for Co-Co, 3.47 A for Gd-Co, and 4.09 A for Gd-Gd. Anelastic deviation of atomic environment A single ion model based on an anelastic deformation of the atomic environment was introduced by Suzuki et al. 4 in order to explain the origin of the perpendicular magnetic
162
Nearest-neighbor ion
4f electron
(
Vertical
sin0
rb sin
RE ion
Horizontal
Cos9
sin0++c
0+ COS
0c/
Magnetic moment
Fig. 3 Schematic single ion model for a perpendicular magnetic anisotropy induced by anelastic deviation of atomic environment.
Fig. 4 Definition of atomic pair distribution index.
anisotropy of RE-TM amorphous thin films. This model refers to the interaction between 4f electrons of a RE atom and its neighbors. Assumed that the density of the nearest-neighbor atoms is higher in the horizontal plane than in the orthogonal plane, the 4f electrons become para
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