Relaxation of thermo-remanent magnetization in Fe-Cr GMR multilayers

TL;DR

This study investigates the decay of thermo-remanent magnetization in Fe-Cr GMR multilayers, revealing a logarithmic relaxation behavior influenced by temperature and structural imperfections, with implications for understanding magnetic dynamics.

Contribution

It provides the first detailed analysis of TRM relaxation in Fe-Cr GMR multilayers, highlighting the temperature-dependent magnetic viscosity and the role of superparamagnetic grains and domains.

Findings

Magnetization relaxation is logarithmic over time.

Magnetic viscosity peaks around the glass transition temperature.

Power law fits better than logarithmic at higher temperatures.

Abstract

The time decay of the thermo-remanent magnetization (TRM) in Fe-Cr giant magnetoresistive (GMR) multilayers has been investigated. The magnetization in these multilayers relaxes as a function of time after being cooled in a small magnetic field of 100 Oe to a low temperature and then the magnetic field is switched off. Low-field ($<$ 500 Oe) magnetization studies of these samples have shown hysteresis. This spin-glass-like behavior may originate from structural imperfections at the interfaces and in the bulk. We find that the magnetization relaxation is logarithmic. Here the magnetic viscosity is found to increase first with increasing temperature, then it reaches a maximum around T$_g$, and then it decreases with increasing temperature. This behavior is different from that of conventional spin glasses where the logarithmic creep rate is observed to increase with temperature. Power law also gives good fits and it is better than the logarithmic fit at higher temperatures. The dynamical effects of these multilayers are related to the relaxation of thermally blocked superparamagnetic grains and magnetic domains in the film layers.