Process-Induced Uniaxial Magnetic Anisotropy in Epitaxial Fe and Ni 80 Fe 20 Films
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Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
environment, and the geometry of deposition may be responsible for this effect. However, only one factor, namely the off-axis position of the Knudsen cells with respect to the normal of the film, has been found to cause this anisotropy in our case. Factors which have been definitely excluded are substrate morphology (such as a stepped surface), film thickness gradients, and residual magnetism of the growth chamber. 3 We have found that it is possible to predict to occurrence and direction of the uniaxial anisotropy simply from the angle of incidence of the incoming Fe flux with respect to the surface.
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Figure 1: Hysteresis loops at T=15K for (a) a Fe(18A)/Pd(21A) superlattice and (b) a 800A-thick Fe film deposited on a (100)MgO substrate, In each case, the stepped loop (open circles) is obtained with the field applied along the cubic axis closest to the direction of the Fe atom flux projected in the plane of the substrate. Uniaxial anisotropy occurs when the projection of the Fe flux in the plane of the substrate is directed preferentially towards one of the in-plane (100) axes, which we call the axis. This axis is consequently always found to be the "hard" (100) axis, i.e., the axis which yields the stepped loop in Figure 1(a). In our MBE system, the Fe flux is 30' away from normal incidence, and its projection in the plane makes a 15' angle with the axis, and a 75' angle with the axis. Thus, the origin of the uniaxial anisotropy component is the angle of incidence of the Fe atom flux with respect to the substrate. Because this effect was first observed in Fe/Pd superlattices with very thin Fe layers (
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