In Situ Analysis of Magnetic and Structural Properties of Epitaxial and Polycrystalline Ni 80 Fe 20 Thin Films
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IN SITU ANALYSIS OF MAGNETIC AND STRUCTURAL PROPERTIES OF EPITAXIAL AND POLYCRYSTALLINE Ni80 Fe20 THIN FILMS
I. Hashim and H.A. Atwater Thomas J. Watson Laboratory of Applied Physics California Institute of Technology, Pasadena, CA 91125
ABSTRACT We have investigated structural and magnetic properties of epitaxial Ni80 Fe2o films grown on relaxed epitaxial Cu/Si(001) films. The crystallographic texture of these films was analyzed in situ by reflection high energy electron diffraction (RHEED), and ex situ by x-ray diffraction and cross-sectional transmission electron microscopy (XTEM). In particular, RHEED intensities were recorded during epitaxial growth, and intensity profiles across Bragg rods were used to calculate the surface lattice constant, and hence, find the critical epitaxial thickness for which Nis 0 Fe20 grows pseudomorphically on Cu(100). XTEM analysis indicated that the epitaxial films had atomically-abrupt interfaces which was not the case for polycrystalline Cu and Nis 0Fe20 film interfaces. The magnetic properties of these epitaxial films were measured in situ using magneto-optic Kerr effect magnetometry and were compared with those of polycrystalline films grown on Si0 2/Si. Large H, (- 35 Oe) was observed for epitaxial Nis 0Fe20 films less than 3.0 nm thick whereas for increasing thickness, H, decreased approximately monotonically to a few Oersteds. Correlations were made between magnetic properties of these epitaxial films, the strain in the film and the interface roughness obtained from XTEM analysis. INTRODUCTION Permalloy (NisoFe 2o) heterostructures are of great interest for magnetoresistive devices based on anomalous antiferromagnetic (AF)-coupling and giant magnetoresistance (GMR) in NisoFe 20/Cu multilayers[1] and spin-valves[2]. To date, all investigations of such Ni8 0Fe 20 heterostructures have employed polycrystalline films with atomically rough interfaces where the interface roughness is of the same order as the nonmagnetic spacer layer thickness[l, 2]. Since AF-coupling and GMR depend sensitively on Nis0Fe 20/Cu interface structure and the film morphology, the magnetotransport properties of atomically-abrupt epitaxial films should more clearly elucidate the underlying physics. Furthermore, with atomically-abrupt film interfaces, it would be possible to fabricate thinner nonmagnetic spacer layers without the interface roughness being the limiting factor. Finally, the growth of epitaxial single layer Nis 0 Fe20 films on silicon is potentially of great interest for studying magnetotransport and for applications to magnetoresistive devices because of reduced interfacial and grain-boundary scattering[3]. Epitaxial NisoFe 20(100) films were grown on a relaxed Cu(001) seed layer, epitaxially grown on Si(001). The epitaxy of Cu at room temperature on H-terminated Si(001) has been the object of earlier investigations[4, 5, 6] and has been successfully demonstrated to occur in high-vacuum and UHV conditions. The mode of this epitaxy was found to take place by occlusion of non-(100) grains b
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