Monte Carlo Simulation of the FM Layer Thickness Influence on the Exchange Bias in FM/AFM Bilayers

Abstract

A Monte Carlo simulation study of the exchange bias properties in ferromagnetic/antiferromagnetic (FM/AFM) bilayers by using a classical Heisenberg model and the Metropolis algorithm is addressed. In our model several contributions including nearest neighbors exchange interactions, two different interface couplings, magnetocrystalline anisotropy, and a Zeeman term were considered. Our study focuses on the influence of FM and AFM layer thicknesses (dF and dA ) on hysteresis loops, particularly exchange bias field (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EB</sub> ) and coercive force (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) . Results reveal that the influence of dA on the exchange bias phenomenon is negligible, while dF produces an important effect on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EB</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . Such behaviors agree with several models and results reported in the literature. Concretely, our model allows inferring a dependence of the exchange bias field with the FM layer thickness proportional to 1/(dF)m characterized by an exponent m = 0.71plusmn0.11. On the other hand, coercive force exhibits a power law increase with the FM layer thickness when thermal fluctuations become relevant. For completeness, thermal stability of the hysteretic properties is finally presented and discussed.