45° Induced Magnetic Anisotropy for Isotropic High-Frequency Permeability

High-frequency permeability spectra and magnetic domain structures of CoZrTa films with 45° induced magnetic anisotropy were investigated in order to realize integrated flux-closed magnetic inductors. Isotropic permeability was experimentally achieved for both in-plane parallel and transversal directions. The obtained relative permeability of ~380 for both the directions of the unpatterned sample is approximately half of the conventional hard-axis permeability as expected from a magnetization rotation model. Once the films are micropatterned, permeability is typically degraded by the formation of spike domains in addition to the demagnetization effect. Through the observations of the magnetic domain structures using magneto-optical Kerr effect microscopy, we found that the formation of the spike domains is suppressed for the smaller patterned structures due to the domain walls along the 45° axis. The relative permeability of ~360 is achieved in the low-frequency range for the micropatterned structure, promising the possibility of flux-closed magnetic inductors with large inductance enhancement.