Driving mechanism for damping and g-factor in non-amorphous ferromagnetic CoFeZr ultrathin films

International audience– We demonstrate that an in-plane uniaxial anisotropy may be induced in non-amorphous soft CoFeZr films. We used broadband ferromagnetic resonance spectroscopy and complex permeability spectra to investigate the spin dynamics in CoFeZr films. We report a systematic study of the FM thickness on the fundamental dynamic parameters such as the effective magnetisation, the g-factor and relaxation mechanisms. Our study reveals that the decrease of the effective magnetisation mesured with FMR with thickness is not due to perpendicular anisotropy but to low dimentionality. Moreover, we observed a decrease of the g-factor with thickness and a modification of the ratio of the orbital to the spin magnetic moment. These films exhibit good high-frequency performance red (i.e. high permeability in a broad frequency range and a low damping) at low thickness of about a few nanometers. Copyright c EPLA, 2016 Nowadays, spintronics devices and magnetic media have to operate at the gigahertz regime (i.e. with ns reversal times). Magnetic thin films are widely used and studied because the ability of their magnetization to precess/reverse in a high frequency-short time range (several GHz/ns) [1,2]. For high-frequency applications, these magnetic materials need to have a large permeabil-ity in a broad frequency range [3]. The key parameters that govern spin dynamics are the saturation magnetiza-tion, the effective field and the (Lande) factor [4]. FeCo alloy should be, at first glance, one of the most competitive candidates because of its high saturation mag-netization M S (2.45 T). However, as-deposited FeCo films exhibit high coercive field ranging from 100 to 200 Oe, in-plane isotropic magnetic anisotropy and a large magne-tocrystalline anisotropy which hinders the high-frequency applications ([5] and references therein). A solution is to produce amorphous CoFe-based alloys by alloying met-alloid into the FM matrix: the addition of a metal-loid in the ferromagnet (FM) destroys the cristallinity, (a