Angular dependence of exchange bias and coercive field in CoFe/MnIr epitaxial bilayers

We have measured the hysteresis loop and torque curves at various applied magnetic field angle in CoFe/MnIr epitaxial bilayers on single crystal MgO [001], (111), and (011) samples. The [001] samples show double shifted magnetization curves, which are dominant as the MnIr thickness increases. It suggests that the unidirectional anisotropy and cubic anisotropy of CoFe [001] layer plays a key role in the formation of double shifted magnetization reversal. The angular variation of exchange bias (Hex) and coercive field (Hc) depend on the orientation of MgO substrates. The measured results are compared with calculated data, which are fitted using the crystalline anisotropy, unidirectional and uniaxial anisotropy induced by the field annealing. The calculated Hex and Hc as a function of measuring angles show similar trend as the measured ones. Theses energy contributions play an essential role in the angle dependent magnetization process in epitaxial CoFe/MnIr bilayers.