The effect of thickness and annealing treatment on microstructure and magnetic properties of amorphous Fe-Si-B-P-C thin films

Abstract

To develop an excellent low-dimensional magnetic material, the evolution of microstructure and soft magnetic properties in thin films with thickness as well as annealing treatment has been systematically investigated. Fe-Si-B-P-C thin films were fabricated using radio frequency magnetron sputtering. Microstructure of as-deposited and as-annealed thin films with various thicknesses have been characterized, and corresponding soft magnetic properties have been studied. The magnetic domain structure in thin films was further characterized via the magneto-optical Kerr microscope. It is revealed that all these as-deposited thin films exhibit a columnar structure, and the surface roughening is in accordance with the anomalous scaling. The coercivity gradually decreases from 4.8 Oe for 61 nm-thick film to 0.6 Oe for 608 nm-thick film, and almost remains constant with further increasing thickness, while the magnetic impedance ratio rises with thickness. After 473 K-annealing treatment coercivity decreases and magnetic impedance ratio increases, which can be attributed to the release of residual stress and the enhanced exchange coupling. After annealing at 573 K, although no obvious improvement in coercivity occurs, magnetic impedance ratio further rises due to the enhanced electrical conductivity and the reduced magnetic anisotropy. Severe crystallization takes place after annealed at 673 K, deteriorating soft magnetic properties of thin films. Therefore, the 573 K-annealed Fe-Si-B-P-C thin film with 1210 nm in thickness exhibits the best soft magnetic properties, having coercivity of 0.3 Oe, magnetic impedance ratio of 66.2% and relatively low magnetic anisotropy, which is a very promising soft magnetic material for sensor application.