Roger Ward

Abstract:

Fe/Mn is a model system in which to study exchange bias, since the antiferromagnetic (AF) Mn layers are believed to have uncompensated moments with all spins aligned in the plane and parallel to those of the Fe. We have determined the microscopic AF ordering at the interfaces using single-crystal neutron diffraction. An unexpected magnetic structure is obtained, with out-of-plane Mn moments perpendicular to those of Fe. This explains the low bias field and shows that the simple AF ordering assumed in a variety of exchange-biased systems may well have to be revised.

Abstract:

Magnetization loops for (110) ErFe2∕YFe2 multilayer films grown by molecular beam epitaxy are presented and discussed. The easy axis for the hard ErFe2 layers is near an out of plane ⟨111⟩-type crystal axis. At low temperatures there is just one irreversible switch of the hard layers, accompanied by the formation of magnetic exchange springs in the soft YFe2 layers. However, above a certain temperature the coercivity changes sign and there are additional high field transitions. This crossover temperature, TCO, depends on the composition of the multilayers. In sufficiently high fields, perpendicular to the multilayer film plane, the energy is minimized by an exchange spring driven multilayer spin-flop state. The composition dependence of TCO is explained with a simple energy argument.