Magnetic anisotropy and reversal in epitaxial FeGa/IrMn bilayers with different orientations of exchange bias br

Epitaxial FeGa/IrMn bilayers with exchange biases along the FeGa[100] and [110] directions are preparedon MgO(001) single crystal substrates by magnetron sputtering through controlling the orientation of theexternal field in situ applied during growth. The effect of the exchange bias orientation on the magneticswitching process and the magnetic switching field are studied. The X-ray j-scan indicates that the FeGa layeris epitaxially grown with a 45 degrees in-plane rotation on the MgO(001) substrate along the FeGa(001)[110] directionand the MgO(001)[100] direction. The measurements of the angular dependence of the ferromagnetic resonancefield and the corresponding fitting to the Kittel equation show that the samples have a superposition of fourfoldsymmetric magnetocrystalline anisotropy , unidirectional magnetic exchange bias anisotropy , anduniaxial magnetic anisotropy with configuration of or . The combined longitudinal andtransverse magneto-optical Kerr effect measurements show that sample with exhibits square loops,asymmetrically shaped loops, and one-sided two-step loops in different external magnetic field directions. Incontrast, the sample with exhibits one-sided two-step and two-sided two-step loops as the magneticfield orientation changes. Because the is superimposed by and , the in-plane fourfold symmetry ofthe magnetic anisotropy energy is broken. The local minima are no longer strictly along the in-plane directions, but make a deviation angle which depends on the relative orientation and strength of magneticanisotropy. A model based on the domain wall nucleation and propagation is proposed with considering thedifferent orientations of , which can nicely explain the change of the magnetic switching route with themagnetic field orientation and fit the angular dependence of the magnetic switching fields, indicating asignificant change of domain wall nucleation energy as the orientation of changes