AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS-ThP

Paper SS-ThP20
Electronic States and Structural Characterization in Single-Crystal Fe-Ni-O Alloy Thin Films Grown by Molecular Beam Epitaxy

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: C.L. Chang, Tamkang University, Taiwan
Authors: C.L. Chang, Tamkang University, Taiwan
G. Chern, Chung-Cheng University, Taiwan
C.L. Chen, Tamkang University, Taiwan
H.H. Hsieh, Tamkang University, Taiwan
W.F. Pong, Tamkang University, Taiwan
T.C. Leung, Chung-Cheng University, Taiwan
Correspondent: Click to Email
Stimulated by the recent success of the research on epitaxial Fe@sub 3@O@sub 4@ and NiO thin films on MgO(001), we extend our study to the growth of a series of alloy Fe-Ni-O thin films with various Fe/Ni concentration ratio by molecular beam epitaxy. Total of 9 samples, around 500 Å thick, are fabricated including Fe@sub 3@O@sub 4@, NiO and Fe@sub x@Ni@sub 1-x@O@sub y@ (x=0.15, 0.3, 0.35, 0.5, 0.56, 0.65, 0.71). These films are expected to show a structural crossover from spinel to rocksalt structure and to show an associated change on valance states of Fe and Ni ions while x varies from 0 to 1. After analyzed by in-situ reflection high energy electron diffraction (RHEED), ex-situ x-ray diffraction, and x-ray absorption spectroscopy (XAS). It is observed that the crystal structure of all the alloy Fe@sub x@Ni@sub 1-x@O@sub y@ films resembles that of the spinel Fe@sub 3@O@sub 4@. The lattice spacing along the perpendicular direction as a function of x shows a minimum at x=0.5 instead of a linear variation indicating that the structures are different from a bulk ferrite Fe@sub 2@NiO@sub 4@-like phase. The distribution of the cations in Fe@sub x@Ni@sub 1-x@O@sub y@ system was studied by Fe and Ni L@sub 2,3@ XAS edge shapes, which are sensitive to the structural symmetry of the sites of the absorbing atoms. The results are qualitatively consistent with the x-ray observations. For x<0.5 Ni ions replace tetrahedral Fe@super 3+@ and octahedral Fe@super 2+@ sites with a ratio of 1:2, and at x=0.5 all the Fe@super 2+@ sites are occupied by Ni ions. Further, for x>0.5 the excessive Ni ions occupy the Fe@super 3+@ sites of tetrahedral and octahedral symmetry up to the x value 0.71. The mechanism of forming the metastable phase and its implication on the magnetic properties of these Fe-Ni-O films will also be discussed. This work is supported by National Science Council of R. O. C. under grands NSC87-2613-M-032-001 and NSC87-2112-M-194-009