Epitaxial growth and interface roughness of PdMn/Fe bilayer structures grown by ion-beam sputtering
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Epitaxial growth and interface roughness of PdMn/Fe bilayer structures grown by ionbeam sputtering Ning Cheng, J.P.Ahn, Werner Grogger, and Kannan Krishnan* Materials Sciences Division, Lawrence Berkeley National Laboratory University of California, Berkeley, CA 94720 Abstract Different orientations of PdMn films and different stacking orders of PdMn and Fe on MgO(001) were studied. At low temperatures (T< 280°C) dominated by the kinetics of growth, a-axis orientated [PdMn(100)/Fe(001)/MgO(001)] was stabilized whilst c-axis [PdMn(001)/Fe(001)/MgO(001)] were obtained at higher temperatures (T> 300°C). The inverted structures, Fe(001)/PdMn(001)/MgO(001) and Fe(001)/PdMn(100)/MgO(001), were obtained epitaxially for the first time. The magnetic exchange coupling (He) of these PdMn/Fe bilayers show a wide range in values: ~ 10 Oe for annealed a-axis samples, ~ 33 Oe for c-axis normal samples and ~ 68 Oe for c-axis inverted samples. The interface roughness of these samples was characterized by energy-filtered transmission electron microscopy (EFTEM). The orientation relationships were confirmed by x-ray diffraction and TEM. The possible origins for the He difference in a-axis and c-axis growth samples and the normal and inverted samples are discussed. Introduction Exchange coupling at the interface between a ferromagnetic (FM) and an antiferromagnetic (AF) layer can cause a unidirectional anisotropy of the FM layer if the samples is grown in a magnetic field or cooled down in a magnetic field after heat ing above the Neel temperature of the AFM layers [1]. It manifests itself by a shift of the hysteresis loop along the field axis and the magnitude of this shift is called the exchange biasing field, He. Exchange biasing between AFM and FM layers in thin film form has attracted considerable technological interest because of the pinning effects of a FM by an AFM in MR sensors and spin-valve heads. Moreover, in spite of the extensive studies conducted on various kinds of exchange-bias systems, its microscopic origin remains a subject of debate [1,2]. NiMn, PtMn, PdPtMn [3]are good candidates for technological applications because of excellent corrosion resistance and large bias field. One of the difficulties in studying the origin of the exchange mechanism in these systems is that it is complicated by the multiphase or polycrystalline nature of the AFM samples. PdMn alloys, belonging to the important family of CuAu-I-type structure, were recently successfully grown epitaxially on MgO(001) by MBE [4]. This system is a good one to understand the exchange mechanism in such technologically important intermetallic AFM systems. Moreover, by studying the spin structure of the bulk PdMn, we found that in the (001), (100) and (010) surfaces, the spin configuration is different. (001) gives a compensated surface while (010) and (100) show an uncompensated surface. It would be of fundamental interest to engineer the growth of these films along different crystallographic orientations to obtain films with (001) or (100) (or(010)) in plane
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