Influence of interfacial exchange coupling on microwave permeability in exchange coupled CoFe/MnIr bilayers

The Co₇₀Fe₃₀(t=100 nm)/MnIr(t_AF nm) bilayers with t_AF=0, 2,4, 10 and 20 were deposited onto a 20 nm Cu buffer layer grown on oxide silicon wafer at room temperature by dc magnetron sputtering method. A magnetic field of 30 Oe was applied during the deposition of bilayers. The CoFe/MnIr bilayers were annealed at 200degC and 340degC for 1 h in a magnetic field of 1 kOe in vacuum along the direction of the applied field during the deposition. The high frequency transverse permeability was measured in the frequency range of 100 MHz to 9 GHz. The H_eb and coercive field (H_c) with field angle was measured with a Magneto-Optic Kerr Effect (MOKE) instrument. The uniaxial and unidirectional anisotropy constant was measured by torque magnetometers in order to obtain the uniaxial and unidirectional anisotropy constant of CoFe layer. The interfacial exchange coupling field has been estimated from the curve fitting of H_eb and coercive field (H_c) with field angle by using the Stoner-Wohlfarth model.