Abstract
A 3.5 nm amorphous CoFeB film was sputtered on GaAs (001) wafer substrate without applying magnetic field during deposition, and a significant in-plane uniaxial magnetic anisotropy (UMA) field (Hu) of about 300 Oe could be achieved. To precisely determine the intrinsic Gilbert damping constant (α) of this film, both ferromagnetic resonance (FMR) and time-resolved magneto-optical Kerr effect (TRMOKE) techniques were utilized. With good fitting of the dynamic spectra of FMR and TRMOKE, α is calculated to be 0.010 and 0.013, respectively. Obviously, the latter is 30% larger than the former, which is due to the transient heating effect during the TRMOKE measurement. In comparison with ordinary amorphous CoFeB films with negligible magnetic anisotropies, α is enhanced significantly in the CoFeB/GaAs(001) film, which may be mainly resulted from the enhanced spin-orbit coupling induced by the CoFeB/GaAs interface. However, the significant in-plane UMA plays minor role in the enhancement of α.
Highlights
In recent years, amorphous CoFeB thin film has been extensively studied owing to its promising application for spintronic devices[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
A significant and pure in-plane uniaxial magnetic anisotropy (UMA) could be achieved in amorphous CoFeB films when they were deposited on semiconductor (e.g. GaAs) films[19,20]
This effect may cause a transient demagnetization of the CoFeB film and/or modify the interface between CoFeB and GaAs, which may result in the fitted value of Hu from time-resolved magneto-optical Kerr effect (TRMOKE) (253 Oe) smaller than that from ferromagnetic resonance (FMR) (292 Oe)
Summary
Amorphous CoFeB thin film has been extensively studied owing to its promising application for spintronic devices[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. In a special case, it was reported that α could reach 0.013 in the Co40Fe40B20 films with in-plane anisotropic field (Hk) to be 50 Oe after the CoFeB films were deposited on Si(100) substrates in magnetic field[15]. In these above studies, α was usually determined by ferromagnetic resonance (FMR) technique. A significant and pure in-plane UMA could be achieved in amorphous CoFeB films when they were deposited on semiconductor (e.g. GaAs) films[19,20]. In order to obtain more reliable and precise value of α, both FMR and TRMOKE techniques were employed simultaneously on this kind of CoFeB films
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