Metastable bcc-Ni and bcc-NiFe Single-Crystal Films Prepared on GaAs Single-Crystal Substrates With Different Orientations

Ni and Ni₈₀Fe₂₀ (at. %) epitaxial thin films are prepared on GaAs single-crystal substrates of (100), (111), and (110) orientations by ultra-high vacuum RF magnetron sputtering. The film growth behavior and the crystallographic properties are studied by reflection high energy electron diffraction and X-ray diffraction. Metastable bcc-Ni and metastable bcc-NiFe single-crystals of (100), (111), and (110) orientations respectively nucleate on GaAs substrates of (100), (111), and (110) orientations, where the bcc structure is stabilized through hetero-epitaxial growth. With increasing the film thickness, the bcc structure in Ni and NiFe films starts to transform into more stable fee structure. The bcc-fcc phase transformation orientation relationships observed for Ni and NiFe films on GaAs(100) and (111) substrates are fcc{100}{011} ||bcc{100}〈 001〉, whereas those for Ni and NiFe films on GaAs(110) substrates are fcc(111)[112̅] ||bcc(110)[11̅0] and fcc(111)[1̅1̅2] ||bcc(110)[11̅0]. The resulting films thus consist of mixtures of bcc and fee crystals. Metastable bcc structure is more stable in Ni film than in NiFe film on all the GaAs substrates. The lattice constants of bcc-Ni and bcc-NiFe crystals are determined to be α_bcc-Ni = 0.292 nm and α_bcc-NiFe = 0.291 nm, respectively. The in-plane magnetization properties of Ni and NiFe films grown on GaAs(110) substrates are reflecting the magnetocrystalline anisotropies of bcc-Ni and bcc-NiFe crystals, respectively.