Gilbert damping in CoFeB/GaAs(001) film with enhanced in-plane uniaxial magnetic anisotropy

Dynamical behaviour of ultrathin [CoFeB (tCoFeB)/Pd] films with perpendicular magnetic anisotropy

CoFeB-based ultrathin films with perpendicular magnetic anisotropy are promising for different emerging technological applications such as nonvolatile memories with low power consumption and high-speed performance. In this work, the dynamical properties of [CoFeB (t_CoFeB)/Pd (10 Å)]₅ multilayered ultrathin films (1 Å ≤ t_CoFeB ≤ 5 Å) are studied by using two complementary methods: time-resolved magneto-optical Kerr effect and broadband ferromagnetic resonance. The perpendicular magnetization is confirmed for multilayers with t_CoFeB ≤ 4 Å. The effective perpendicular magnetic anisotropy reaches a clear maximum at t_CoFeB = 3 Å. Further increase of CoFeB layer thickness reduces the perpendicular magnetic anisotropy and the magnetization became in-plane oriented for t_CoFeB ≥ 5 Å. This behaviour is explained by considering competing contributions from surface and magnetoelastic anisotropies. It was also found that the effective damping parameter α_eff decreases with CoFeB layer thickness and for t_CoFeB = 4 Å reaches a value of ~ 0.019 that is suitable for microwave applications.

Large anisotropy of magnetic damping in amorphous CoFeB films on GaAs(001)

Amorphous CoFeB films grown on GaAs(001) substrates demonstrating significant in-plane uniaxial magnetic anisotropy were investigated by vector network analyzer ferromagnetic resonance. Distinct in-plane anisotropy of magnetic damping, with a largest maximum-minimum damping ratio of about 109%, was observed via analyzing the frequency dependence of linewidth in a linear manner. As the CoFeB film thickness increases from 3.5 nm to 30 nm, the amorphous structure for all the CoFeB films is maintained while the magnetic damping anisotropy decreases significantly. In order to reveal the inherent mechanism responsible for the anisotropic magnetic damping, studies on time-resolved magneto-optical Kerr effect and high resolution transmission electron microscopy were performed. Those results indicate that the in-plane angular dependent anisotropic damping mainly originates from two-magnon scattering, while the Gilbert damping keeps almost unchanged.

Ferromagnetic resonance studies of strain tuned Bi:YIG films

Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large magneto-optical activity with low losses still need to get probed for its magnetization dynamics. We demonstrate a controlled tuning of magnetocrystalline anisotropy in Bi-doped Y₃Fe₅O₁₂ (Bi:YIG) films of high crystalline quality using growth induced epitaxial strain on [1 1 1]-oriented Gd₃Ga₅O₁₂ (GGG) substrate. We optimize a growth protocol to get thick highly-strained epitaxial films showing large magneto-crystalline anisotropy, compare to thin films prepared using a different protocol. Ferromagnetic resonance measurements establish a linear dependence of the out-of-plane uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG lattice. Interestingly, the enhancement in the magnetoelastic constant due to an optimum substitution of Bi³⁺ ions with strong spin orbit coupling does not strongly affect the precessional damping (∼[Formula: see text]). Large magneto-optical activity, reasonably low damping, large magnetocrystalline anisotropy and large magnetoelastic coupling in Bi:YIG are the properties that may help Bi:YIG emerge as a possible material for photo-magnonics and other spintronics applications.

Component manipulated magnetic anisotropy and damping in Heusler-like compound Co2+x Fe1-x Al

The component dependence of the magnetocrystalline anisotropy and the damping has been investigated in epitaxial Heusler-like compound Co_2+x Fe_1-x Al films grown by molecular beam epitaxy (MBE) with x  =  -0.4, -0.2, 0, 0.2, and 0.4. All the films show a component tunable four-fold magnetocrystalline anisotropy with the easy axis along [1 1 0] orientation. The time resolved magneto-optic Kerr effect measurements reveal that the damping constant can be tuned in a range of 0.0065-0.0156 with a minimum value of 0.0065 at x  =  -0.2. This work provides a new approach to manipulate the magnetic dynamic properties of Heusler alloy Co₂FeAl by adjusting the proportion of Co and Fe.