The manipulation of magnetization damping in FeNi1–xNdx/Cu/FeCo1–yGdy sandwich structured multilayers

Abstract

The magnetic properties and magnetization damping in a series of Ta(5 nm)/Fe20Ni80Nd0.075(3 nm)/Cu(tCunm)/Fe50Co50Gd0.07(3 nm)/Cu(2 nm) multilayers with varying nonmagnetic Cu layer thickness are investigated by vibrating sample magnetometer and ferromagnetic resonance (FMR). Two-step hysteresis loops are observed, indicative of individual switching of the two magnetic layers. The saturation magnetization of the multilayers possesses a very close magnitude to the sum of those for the Fe20Ni80Nd0.075 and Fe50Co50Gd0.07 single layer films, and the difference between each other is within 3% only. Element-specific hysteresis loops of each magnetic elements involved the multilayers are further probed by x-ray magnetic circular dichroism, which reveals that Fe, Ni, and Co are ferromagnetically coupled with Nd and anti-ferromagnetically with Gd. The FMR spectra for the multilayers exhibit two-resonance peaks originated from the two magnetic layers. Compared with the NiFe-Nd and FeCo-Gd single magnetic films, the linewidth of NiFe-Nd layer in the multilayers shows a large enhancement, while that of the FeCo-Gd layer decreases. Theoretical fitting of the FMR data indicates that the contribution of two-magnon scattering has played an important role in the observed linewidth of single FeCo-Gd films, which, in turn, causes the larger FMR linewidth than that in the multilayers. The intrinsic Gilbert damping constant of both FeNi-Nd and FeCo-Gd layers is found to increase with increasing thickness of nonmagnetic Cu layer from 0.8 nm to 2 nm.