Impact of the transverse magnetocrystalline anisotropy of a Co coating layer on the magnetoimpedance response of FeNi-rich nanocrystalline ribbon

There is a pressing need for improving the high-frequency magneto-impedance (MI) response of cost-effective soft magnetic materials for use in high-performance sensing devices. We report here a comparative study of uncoated (Fe50Ni50)(81)Nb7B12 nanocrystalline ribbons and ribbons coated with 120 nm of Co on both surfaces. The impact of the Co coating on the high frequency impedance of the (Fe50Ni50)(81)Nb7B12 ribbon was studied with techniques sensitive to surface magnetism, namely magneto-optical Kerr effect (MOKE), MOKE microscopy, and high frequency impedance as a function of magnetic field. MOKE microscopy on the coated ribbons showed a superposition of high anisotropy domains from the crystalline Co and wide magnetic domains from (Fe50Ni50)(81)Nb7B12. In full agreement with the MOKE results, MI measurements indicated an increase in anisotropy field in the excitation frequency range 100-1000 MHz in the Co-coated ribbons. Noticeably, the Co-coating improved the MI ratio by 15% at fields near and below the anisotropy field. The improvement of the low-field MI response by the coating encourages the use of magnetic coatings to improve MI-based sensors in ribbon geometry for technological applications such as biomagnetic sensing. This study also yields insights into the effects of negative magnetostrictive coatings on the MI behavior in soft magnetic ribbons. (C) 2018 Elsevier B.V. All rights reserved.