Effects of composition and temperature of crystallization on the microstructure and magnetic properties of NdFeB thin films for perpendicular recording media

Abstract

NdFeB thin films were synthesized by a dc magnetron sputtering system. The influence of composition and temperature of crystallization on the microstructure and magnetic properties of NdFeB thin films was investigated. It was found that excessive Nd and B addition was helpful in promoting granular structure and reducing grain growth as well as in modifying magnetic properties. The excess elements were precipitated and well distributed around the shells of hard magnetic grains. This actively decreased the intergranular interactions between hard grains. Films made on heated substrate were also compared to those fabricated by post annealing. The former method was proved to be very effective to produce hard NdFeB thin films with good perpendicular anisotropy on a W underlayer, whereas films made by the latter process were isotropic. The maximum coercivity was obtained near 10 kOe in films annealed at 600 °C. The intergranular interactions were characterized by δM plots. It was found that annealed samples have a much stronger exchange coupling interaction than do the in situ deposited samples. Therefore, the magnetization reversal process in annealed films is mainly controlled by domain wall motion while it is more likely to be dominated by incoherent magnetization reverse in in situ deposited thin films, defined by the dependence of coercivity Hc(θ) on the measuring angle θ. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)