In-plane magnetic anisotropy of bcc Co on GaAs(001)

Abstract

Epitaxial growth of Co on GaAs͑001͒ and its in-plane magnetic anisotropy are studied using reflection high-energy electron diffraction, a high-resolution transmission electron microscope, and the magneto-optical Kerr effect. In the initial and final stages of growth, Co exists in single-crystalline body-centered-cubic ͑bcc͒ and hexagonal-closed-packed ͑hcp͒ phases, respectively, while in the middle stage the coexistence of the bcc and hcp structures is observed. For the bcc Co thin films on GaAs͑001͒, a fourfold in-plane magnetic anisotropy with easy axes along the ͗100͘ directions is realized and discussed. ͓S0163-1829͑98͒04915-7͔The 3d transition metals exist in a variety of crystallographic and magnetic phases. Thin-film growth of these materials on crystalline substrates allows the forces present at the interface to drive the film into specific crystalline structures. These structures may be in a thermodynamically stable phase, a known high-pressure or high-temperature phase, or even a phase not previously observed. They greatly increase the variety of magnetic materials by essentially making ''new'' materials from ''old'' elements. 1The epitaxial growth of Co films serves as a good example. It is known that the hexagonal-close-packed ͑hcp͒ and face-centered-cubic ͑fcc͒ structures are, respectively, stable and metastable phases of Co. The body-centered-cubic ͑bcc͒ structure, which does not occur in nature, was realized by Prinz with epitaxial growth on a GaAs͑110͒ substrate. However, it was later pointed out by Liu and Singh that bcc Co is not a true metastable phase but a force-induced phase. 3The in-plane magnetic anisotropy of such a bcc Co thin film on GaAs͑110͒ was further determined and a negative value for the cubic anisotropy constant K 1 was proposed.2 If this were true, a fourfold in-plane magnetic anisotropy with easy axes along the ͗110͘ direction would then be expected in the bcc Co films on GaAs͑001͒ substrates. In fact, a fourfold in-plane magnetic anisotropy with the easy axes along the ͗100͘ rather than the ͗110͘ direction was observed by Blundell et al. 4 Interestingly, it was later argued by Gu et al. that Co films grown on GaAs͑001͒ were actually not bodycentered cubic but two-domain hexagonal close packed by which the fourfold magnetic anisotropy along the ͗100͘ direction could be explained by such a microstructure.5 Obviously, the epitaxial structure of Co on GaAs͑001͒ and its magnetic anisotropy are still very controversial. In this work, we present a clear picture of the epitaxial growth of Co on GaAs͑001͒, which clears up the previous controversy about the structure of Co thin films on GaAs͑001͒. With the help of this clear picture, we prove that the bcc Co films on GaAs͑001͒ show a fourfold in-plane magnetic anisotropy.Co films were grown in a molecular-beam epitaxy ͑MBE͒ growth chamber connected with the VG-ESCALAB-5 electron spectrometer system. The Te-doped GaAs͑001͒ singlecrystal wafers were polished and treated by ordinary device cleaning process. The final substrate cleaning w...

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.…”