Surface Anisotropy in Epitaxial FE(110)/MO(110) Multilayers
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ABSTRACT We have prepared epitaxial Fe(110)/Mo(110) multilayers by sputter deposition. These films exhibit a large uniaxial anisotropy and may be attractive as islanded in-plane recording media. The large uniaxial anisotropy is due to the intrinsic surface anisotropy of the Fe(110)/Mo(110) interface, which is of the same magnitude as the surface anistropy of the Fe(110)/W(110) interface but has a different sign (the surface anisotropy of the Fe(110)/Mo(110) interface prefers the [001] axis of magnetization). The magnetoelastic component of the anisotropy is not large. A novel magneto-optic technique was used to measure the transverse component of the magnetization and deduce information about the anisotropy and domain structure of the multilayers. INTRODUCTION Interest in single crystal materials with a large in-plane anisotropy has been spurred recently by attempts to pattern islands in single crystals for in-plane recording media. Each island would represent one bit, and it is therefore essential to have a strong uniaxial anisotropy that will pin the magnetization along a certain axis 1 . An obvious candidate for uniaxial anisotropy is the [110] surface with its two-fold symmetry. However, the [110] surface also has a large biaxial term in the anisotropy 2 which must be overcome with other uniaxial anisotropy mechanisms, such as surface or magnetoelastic anisotropy. Multilayers are a logical choice for enhancing the uniaxial anisotropy because of their propensity to have high surface and magnetoelastic energies3 . We prepared Fe/Mo multilayers in an attempt to increase the uniaxial component of the anisotropy, studied their mechanical properties, and measured their magnetic anisotropy with torque magnetometry and the Magneto-Optic Kerr Effect (MOKE).
EXPERIMENTAL Samples were synthesized by DC magnetron sputtering in a custom-built UHV chamber with a base pressure of 3.Oxi-o torr. Single crystal (1120)-oriented A12 0 3 substrates were cleaned with solvents and heated above 650'C for deposition of a 600 ml Mo (110) underlayer. Previous work has shown that Mo grows epitaxially on the A120 3 with the [ill] direction parallel to the [0001] axis of the A1203' 5 . The Fe/Mo multilayer was deposited at room temperature by alternately opening and closing shutters in front of the sputtering guns. The first layer deposited on the Mo underlayer was Fe and the top layer was Mo. All samples were capped by at least 50A of Mo. Thicknesses were determined by calibration runs and rate monitors. A total of eight multilayers were prepared. All multilayers had approximately 500 monolayers ('ml') each of Fe(110) and Mo(110) with bilayer periods ranging from 15 ml Fe plus 15 ml Mo (51si) to 100 ml Fe plus 100 ml Mo (426A). The epitaxies of both the Mo under209 Mat. Res. Soc. Symp. Proc. Vol. 384 @1995 Materials Research Society
layer and the multilayer were determined by x-ray diffraction using laboratory sources and verified at the Stanford Synchrotron Radiation Laboratory (SSRL). The magnetic properties of the samples were measur
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