Structure induced magnetic anisotropy behavior in Co/GaAs(001) films

Abstract

Epitaxial Co has been grown on GaAs(001) and studied by both low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED), and by the magneto-optic Kerr effect (MOKE) and polarized neutron reflection (PNR). Three samples were fabricated using different growth procedures: (1) ‘‘interrupted’’ growth (including an anneal); (2) and (3) continuous growth of similar thicknesses. For sample 1, RHEED patterns indicate an initial growth in the bcc phase followed by a relaxation into a distorted single phase at completion of growth, whereas samples 2 and 3 showed a multicrystalline structure after growth. LEED patterns were used to check the existence of the 2×4 reconstruction patterns before growth, but no LEED patterns could be obtained after more than 2 Å Co was deposited, in contrast to the RHEED patterns which remained visible throughout the growth. Structural analysis of the completed films indicates the formation of a ∼10 Å CoO layer on the Co/air interface, and gives thicknesses for magnetic material of (1) 30 Å and (2) 80 Å. Sample 1 showed a dominant fourfold magnetic anisotropy with the easy axis parallel to the (100) direction and with a strength 2K4/M of ∼0.5 kOe, smaller in magnitude than that reported for bcc films on GaAs(110) but along the same axis [G. A. Prinz et al., J. Appl. Phys. 57, 3672 (1985)]. However, samples 2 and 3 showed only a large uniaxial anisotropy along the (110) direction of strength 2K1/M of ∼1.5 kOe and ∼2.5 kOe, respectively, similar in magnitude to those previously observed [G. A. Prinz et al., J. Appl. Phys. 57, 3676 (1985)]. We attribute the origin of the contrasting magnetic anisotropy behavior observed to the differences in final structure.

Growth of epitaxial bcc Co(001) electrodes for magnetoresistive devices

“…11,12,[22][23][24][25][26] The fact that thicker layers were not obtainable agrees well with the theoretical prediction that bcc Co is not metastable, but strain induced. 16 We also tried to grow bcc Co directly on GaAs͑001͒ instead of on an Fe buffer layer.…”

“…less than 3 nm͒ for various substrates ͑including GaAs͒ and crystal orientations. 11,12,[22][23][24][25][26] This implicates that the stability of the grown layers has to be checked carefully every time. In Sec.…”

“…11,12,[22][23][24][25][26] The exact value depends sensitively on the growth method, temperature and speed, and on the specific substrate. The most frequently used substrates, apart from GaAs, are Fe and Cr.…”

Co thin film with metastable bcc structure formed on GaAs(111) substrate

“…The resulting film structure was investigated by 2T/Z-scan out-of-plane, 2TF/ij-scan in-plane, and pole-figure X-ray diffractions (XRDs) with Cu-KD radiation (O = 0.15418 nm). A Co single-crystal film with metastable A2 structure is obtained in an early stage of film growth on GaAs(111) substrate, similar to the cases of films deposited on GaAs(100) [4][5][6][7] and GaAs(110) [4,8,9] substrates. The These relationships are similar to the NishiyamaWasserman orientation relationship [10,11].…”

“…Formation of A2 phase has been recognized for Co films of a few nm thicknesses grown on GaAs substrates of (100) [4][5][6][7] and (110) [4,8,9] orientations by molecular beam epitaxy. With increasing the thickness, most of the A2-Co crystals tended to transform into more stable A3 or A1 crystals.…”