Competing Anisotropies and Temperature Dependence of Exchange Bias in Co|IrMn Metallic Wire Arrays Fabricated by Nanoimprint Lithography

The magnetic behavior of exchange biased Co|IrMn bilayer metallic wire arrays, fabricated by nanoimprint lithography, was studied and compared with identical thin film heterostructures. A significant uniaxial shape anisotropy, K U-shape , in addition to the unidirectional exchange anisotropy, K E , and the intrinsic uniaxial anisotropy, K U-intrinsic observed in the unpatterned film, was introduced in the wire arrays through wire patterning. The competing anisotropies were shown to modify the angular dependence of exchange bias, H EB , and coercivity, H C , for wire arrays. In addition, an asymmetric behavior is observed for both wire arrays and unpatterned film and is attributed to the noncollinear alignment of uniaxial and unidirectional anisotropies. Temperature dependence of H EB is different for the wire arrays from the unpatterned thin film. This and the large deviation from ideal cubic anisotropy in the antiferromagnet for the wire arrays are both in agreement with Malozemoff’s model of exchange bias.