Temperature dependence of exchange biased thin films

A thin ferromagnet exchange coupled to an antiferromagnet often results in an enhanced width and a shift in the center position for the hysteresis cur ve. Recent calculations have shown how these features could occur in for bo th compensated and uncompensated antiferromagnet interfaces. These calculat ions were performed at zero temperature. We explore a model which allows fo r imperfectly compensated interfaces due to interface roughness and which c alculates the spin configurations and hysteresis curves as a function of te mperature. We find that the Koon results-ferromagnet spins directed perpend icular to the antiferromagnet spins-is appropriate for low temperature and nearly compensated interfaces. Increasing temperature and noncompensation f avors a configuration where the ferromagnetic spins line up closer to the e asy axis of the antiferromagnet. A particularly interesting result is that the coercive field decreases much more rapidly than the bias field as tempe rature is increased. This is in agreement with some recent experimental res ults, and we speculate that the exchange bias is substantially due to the s urface structure of the antiferromagnet while the coercive field depends on the behavior of the spins in the bulk of the antiferromagnet. (C) 2000 Ame rican Institute of Physics. [S0021-8979(00)86108-3].