Anomalous Hall effect in epitaxially grown ferroemagnetic FeGa-Fe3Ga hybrid structure- evidence of

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localization of stresses, and in amorphous ferromagnets with spatial fluctuations of the anisotropy constant, which is strongly dependent on sample thickness. 23 , 24 The AHE has been mainly reported in inhomogeneous magnetic materials, such as magnetic clusters embedded in a semiconductor, or a metal, or an oxide, etc., which is suggested to be associated with spin carrier polar- ization by clusters. Although a number of theoretical models have been proposed to explain the observed effects, no direct ex- perimental evidence has been reported. 7 10 In addition, the mag- netic anisotropy of clusters is often randomly distributed in a host matrix (metal, insulator or semiconductor, etc.) that makes difficult to separate intrinsic and extrinsic phenomena. In this work, we present a method that provides direct evidence for spin carrier polarization by clusters by investi- gating the shape of saturated Hall resistance. To analyze this model, we used the in-plane magnetic anisotropy of Fe-Ga and out-of-plane magnetic anisotropy of Fe 3 Ga clusters em- bedded in Fe-Ga hybrid structure. The 1000A ˚ thick Fe 68.3 Ga 31.7 thin films were grown on a semi-insulating GaAs(001) substrate using MBE (molecular beam epitaxy, VG Semicon, Inc.) at 300, 400, and 500 ² C by coevaporating Fe and Ga, which was monitored by a quartz thickness micro balance. The detailed preparation and growth process of GaAs(001) substrates have been reported else- where. 25 The growth quality of the thin films was monitored by in situ reflection high-energy electron diffraction (RHEED). The surfaces of the films were characterized by atomic force micros- copy (AFM) and field emission scanning electron microscopy (FE-SEM). The crystal structure of the samples was character- ized by X-ray diffraction (XRD). Figures 1(a) 1(d) show the RHEED patterns of the GaAs(100) wafer and samples grown at 300, 400, and 500 ² C, respectively. Well defined streaks were observed for the films grown at 300 and 400 ² C, indicating that the films are the epitax- ially grown and have smooth surface morphologies, as shown in Figs. 1(b) and 1(c) . The change from the streaks to spotty pat- tern was observed for films grown at 500 ² C, as shown in Figure 1(d) , indicating that the films were epitaxially grown with an island 3D growth mode and has the rough surface. Figure 2 shows AFM images of 1000 A ˚ Fe-Ga films grown at different temperatures. The average roughnesses of the thin films are determined to be 5.2, 7.6, and 9.2 nm for growth temperature of 300, 400, and 500 ² C, respectively. With increasing growth temperature, the surface morphology is gradually roughened. Figs. 2(d) 2(f) show the surface of the films with different growth temperatures. The homogene- ous films were obtained for all samples.
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