Interfacial spin order in exchange biased systems

The phenomenon of exchange bias in which a ferromagnet is grown in intimate contact with an antiferromagnet leads to a shifted hysteresis loop. All analytical theories developed to explain this effect predict values of the shift of the loop that are too large, often by an order of magnitude. In many numerical models an interface exchange coupling constant C* is introduced to account for these discrepancies. In this work we describe a series of experiments, which reveals the temperature and field dependence of this interfacial spin order that account for the weakened coupling between the layers. We also show that this order has a marked temperature dependence at temperatures down to similar to 50 K. At temperatures below 50 K we observe a sudden marked increase in the observed exchange bias of up to a factor of 2, which we attribute to a spontaneous spin ordering of the interfacial spins analogous to that which occurs in spin-glass systems. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3005877]