Giant magnetoresistance in PtMn alloys

The onset of chemical and magnetic order in PtMn is accompanied by a large increase in the resistivity, rho, contrary to that observed in nonmagnetic or ferromagnetic disorder-order transitions. We attribute this to a giant magnetoresistance like magnetic scattering off the antiferromagnetically aligned spins within the PtMn. The characteristics of the resistance change with anneal time in two regimes, with only the second regime involving a disorder/order transition. We have used the change of rho with time to calculate the activation energy for the L1(0) transformation in PtMn and found it to be about 1.5 eV for thick films. The activation energy increases significantly for thinner films. (C) 2004 American Institute of Physics.