Exchange biasing by Ir19Mn81: Dependence on temperature, microstructure and antiferromagnetic layer thickness

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Abstract
We have investigated the thermal stability of the exchange biasing interaction in antiferromagnetic/ferromagnetic bilayers of Ir19Mn81 and Ni80Fe20 or Co90Fe10. The exchange-biasing field and the coercive field were found to depend strongly on the thickness of the Ir19Mn81 layer and on the crystallographic texture of the bilayer. The exchange-biasing field at room temperature has a maximum at 4 nm Ir19Mn81 layer thickness and then decreases for increasing Ir19Mn81 layer thickness. This coincides quite well with the thickness dependence of the (111) texture measured in Ir19Mn81 layers. Removing the Ta seed layer resulted in the disappearance of the (111) texture and at the same time the exchange-biasing field decreased for all Ir19Mn81 layer thicknesses. For films with a Ta seed layer and 8 nm Ir19Mn81 or more, we have found a blocking temperature of 560 K, decreasing with decreasing Ir19Mn81 layer thickness to around room temperature for 2 nm Ir19Mn81. Removing the Ta seed layer resulted in a decrease of the blocking temperature for all layer thicknesses investigated. We have concluded that the (111) texture is an important factor governing the size of the exchange-biasing field and the thermal stability.