Unified nonequilibrium dynamical theory for exchange bias and training effects

TL;DR

This paper presents a unified dynamical simulation approach to study exchange bias and training effects in FM/AF heterostructures, revealing how these phenomena depend on temperature, cooling rate, and magnetic interactions.

Contribution

The study introduces a reliable Monte Carlo dynamical method to simulate exchange bias and training effects, providing insights into their microscopic origins and control mechanisms.

Findings

Exchange bias shifts are observed below 45 K.

Exchange bias decreases with slower cooling and more field cycles.

Manipulation of exchange bias via cooling rate and anisotropy distribution.

Abstract

We investigate the exchange bias and training effects in the FM/AF heterostructures using a unified Monte Carlo dynamical approach. This real dynamical method has been proved reliable and effective in simulating dynamical magnetization of nanoscale magnetic systems. The magnetization of the uncompensated AF layer is still open after the first field cycling is finished. Our simulated results show obvious shift of hysteresis loops (exchange bias) and cycling dependence of exchange bias (training effect) when the temperature is below 45 K. The exchange bias fields decrease with decreasing the cooling rate or increasing the temperature and the number of the field cycling. With the simulations, we show the exchange bias can be manipulated by controlling the cooling rate, the distributive width of the anisotropy energy, or the magnetic coupling constants. Essentially, these two effects can be explained on the basis of the microscopical coexistence of both reversible and irreversible moment reversals of the AF domains. Our simulated results are useful to really understand the magnetization dynamics of such magnetic heterostructures. This unified nonequilibrium dynamical method should be applicable to other exchange bias systems.