Efective magnetic anisotropy obtained using FMR and VSM in FeNi nanowires with dipolar interactions

J. ALMEIRA; C. RAMOS; J. MILANO; F. MENESES; S. E. URRETA; P. G. BERCOFF

Workshop; International Workshop on Spintronics 2022 (SPIN Argentina); 2022

Ferromagnetic Resonance (FMR) is best suited to determine symmetry and magnitude of the magnetic anisotropy, and it generally coincides with the values derived from magnetization measurements, M(H). In this work we present results of the effective anisotropy field (HA) using FMR (at 34 GHz) and M(H) as a function of the angle between the NW and the applied field, H, in nanowire (NW) arrays of Fe(x)Ni(100-x) (x = 15, 25, and 38) grown into ordered nanoporous alumina templates. Both, FMR and M(H) indicate that the NW growth direction is the easy axis. Also M(H) shows negligible hysteresis for H  NW (hard axis), as expected for a uniaxial shape anisotropy of polycrystalline NW. We used the angular variation of FMR and the areas of M(H) between H//NW and H_|_NW to extract HA. The values determined from FMR and M(H) show similar trends with x. However, the magnitudes of HA are quite different: HA obtained from M vs H is between 50% and 300% larger than HA obtained from FMR. This contrasts with previous reports that show a much closer match between M(H) and FMR [1, 2], suggesting that the internal degrees of freedom involved in the static and dynamic processes in M(H) and FMR need to be taken into account to understand and model these experimental findings.