Texture Effects in IrMn/CoFe Exchange Bias Systems

We report an enhancement of the average blocking temperature ${≪}{\rm T}_{\rm B}{>}$ in IrMn/CoFe exchange bias systems due to an increase in the anisotropy constant of the IrMn. This is related to a (111) texture of IrMn parallel to the interface. Si${≪}100{>}$ /Seed (5 nm)/IrMn (10 nm)/CoFe (3 nm)/Ta (10 nm) were prepared by dc sputtering. Cu, Ru, and NiCr seed layers were used. X-ray diffraction studies involving both $\theta/2\theta$ and grazing incidence scans revealed a strong (111) texture of the IrMn parallel to the interface for the samples with a NiCr seed layer. Cu and Ru seed layers did not cause a marked texture. Thermal activation measurements found an enhancement of the average blocking temperature from 367 K for the sample with Cu seed layer to 477 K for the sample with a NiCr seed. The anisotropy constant was found to increase from $(2.8 {\pm} 0.2) \times 10^{6}$ erg/cm $^{3}$ for the sample with a Cu seed layer to $(3.3 \pm 0.4) \times 10^{7}$ erg/cm$^{3 }$ for the sample with a NiCr seed layer. We find that the increase in the anisotropy constant leads to an enhanced blocking temperature.