Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 33: Magnetic Coupling Phenomena/ Exchange Bias

MA 33.10: Talk

Wednesday, March 28, 2012, 17:45–18:00, EB 202

Spin-structure and spin-reorientation transitions in the CoPd/ IrMn exchange bias system. — •Muhammad Bilal Janjua and Gernot Güntherodt — II. Physikalisches Institut A, RWTH Aachen University, 52074 Aachen, Germany.

In MBE grown polycrystalline Co22Pd78/ Ir25Mn75 thin films with [111] texture, a transition in the exchange bias (EB) is observed at low temperatures, where the in-plane EB field becomes greater than the out-of-plane EB field. Despite the out-of-plane magnetization of CoPd at low temperatures, this behavior of EB is an evidence of the change in the spin structure of the antiferromagnet (AFM) IrMn. It is found that with decreasing temperature there is a spin structure transition in IrMn thin films related to the 3Q to 2Q transition in the bulk [1], which implies a change of the AFM spin structure from an out-of-plane component (3Q) to in-plane component (2Q). This transition is responsible for the increase in the in-plane EB at low temperatures. Besides the 3Q-2Q transition of IrMn, a spin reorientation transition from out-of-plane to in-plane (at higher temperatures) is also observed in the thermoremanent magnetization of Co22Pd78(t nm)/Ir25Mn75(15nm) for different thicknesses t. This effect is due to CoPd, but is too weak to perturb the spin structure transition of IrMn, which dominates the temperature dependence of EB.

[1]. A. Sakuma, K. Fukamichi, K. Sasao and R. Y. Umetsu, Phys. Rev. B 67, 024420 (2003).