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 curve. Recent calculations have shown how these features could occur in for both compensated and uncompensated antiferromagnet interfaces. These calculations were performed at zero temperature. We explore a model which allows for imperfectly compensated interfaces due to interface roughness and which calculates the spin configurations and hysteresis curves as a function of temperature. We find that the Koon results-ferromagnet spins directed perpendicular to the antiferromagnet spins-is appropriate for low temperature and nearly compensated interfaces. Increasing temperature and noncompensation favors a configuration where the ferromagnetic spins line up closer to the easy axis of the antiferromagnet. A particularly interesting result is that the coercive field decreases much more rapidly than the bias field as temperature is increased. This is in agreement with some recent experimental results, and we speculate that the exchange bias is substantially due to the surface structure of the antiferromagnet while the coercive field depends on the behavior of the spins in the bulk of the antiferromagnet. (C) 2000 American Institute of Physics. [S0021-8979(00)86108-3].