Enhancement of exchange bias in Ir–Mn/Co0.9Fe0.1 bilayers by inserting an ultra-thin Co0.6Fe0.4 layer

Abstract

The exchange biasing of Co0.9Fe0.1 film by the antiferromagnet Ir–Mn via a thin intermediate Co0.6Fe0.4 layer was investigated. It has been found that the exchange bias is drastically enhanced with the insertion of an ultra-thin Co0.6Fe0.4 layer at the interface between Co0.9Fe0.1 and Ir–Mn layers. For the Ir0.25Mn0.75(100 Å)/Co0.9Fe0.1(150 Å) bilayer, the pinning field at room temperature is raised from 92 to 206 Oe when a 4 Å Co0.6Fe0.4 layer is introduced at the interface, and further enhanced to 262 Oe with a 10 Å Co0.6Fe0.4 insertion layer. The corresponding unidirectional anisotropy increases from 0.18 to 0.4 erg cm−2 and reaches a value of 0.54 erg cm−2. The extra large unidirectional anisotropy is maintained as the Co0.6Fe0.4 thickness exceeds 10 Å. The high blocking temperature of the Ir–Mn/Co0.9Fe0.1 bilayer is unaffected by the insertion of the Co0.6Fe0.4 layer. The present results indicate that exchange bias is essentially determined by interfacial spins and, most importantly, the performance of the exchange bias system Ir–Mn/Co0.9Fe0.1, which is commonly used in spin valve giant magnetoresistance devices, can be greatly promoted by the insertion of an ultra-thin interfacial Co0.6Fe0.4 layer.