Damping by slow relaxing rare earth impurities in Ni80Fe20

TL;DR

This paper investigates how doping NiFe with rare earth impurities affects magnetic relaxation, explaining the effects through a slow relaxing impurity mechanism linked to anisotropic exchange interactions, and measures the relaxation times of 4f electrons.

Contribution

It introduces a model based on slow relaxing impurities to explain damping in NiFe doped with rare earths and provides experimental measurements of 4f electron relaxation times.

Findings

Damping effect scales with exchange anisotropy.

Damping increases by an order of magnitude at low temperatures.

Relaxation times of 4f electrons vary with temperature.

Abstract

Doping NiFe by heavy rare earth atoms alters the magnetic relaxation properties of this material drastically. We show that this effect can be well explained by the slow relaxing impurity mechanism. This process is a consequence of the anisotropy of the on site exchange interaction between the 4f magnetic moments and the conduction band. As expected from this model the magnitude of the damping effect scales with the anisotropy of the exchange interaction and increases by an order of magnitude at low temperatures. In addition our measurements allow us to determine the relaxation time of the 4f electrons as a function of temperature.