Enhanced coercive force of Nd-Fe-B thin films by the introduction of a Cr underlayer

We investigated the influence of a Cr underlayer on the structure and magnetic properties of Nd-Fe-B thin films which were produced by a conventional rf sputtering method. The thickness of the underlayer and the substrate temperature were varied from 0 to 5000 A and from room temperature to 670 C, respectively. It was found that the thickness of the underlayer material and the substrate temperature strongly influenced the crystal orientation and magnetic properties. The main crystalline phase was Nd2Fe14B, whose tetragonal c-axis was aligned perpendicularly to the film plane. A high coercive force (Hc=3.7 kOe) was achieved using the following conditions: Cr underlayer with a thickness of 500 A and a substrate temperature of 650 C. From TEM observation, this enhanced coercive force is thought to be attributable to a modification of the columnar structure. (orig.)