Permanent magnet design assisted by antiferromagnet-ferromagnet interface coupling: A Monte Carlo study

In the pursuit of rare-earth-free permanent magnets, materials with large saturation magnetization (M_s) stand out. However, large M_s results in low anisotropy field, thus additional source of coercivity is needed to make useful magnets for a broad range of applications. In this paper, we investigate the use of interface coupling to an antiferromagnet (AFM) as a means to increase coercivity for permanent magnet design. Results on the effects of Néel temperature, AFM anisotropy, interface coupling strength, AFM volume ratio, as well as temperature dependence are obtained using Monte Carlo (MC) simulations. And before that, we clarify some practices in MC simulations of magnetic hysteresis. The origin of coercivity enhancement is investigated by examining the magnetization reversal process, which is found to agree with well-established theory of exchange bias. Finally, discussions and design suggestions are made on the AFM materials, the geometry, and experimental realization.