Effect of Cr on the hard magnetic properties and the microstructure of sputtered Nd-Fe-B-Cr thin films

We investigated the influence of Cr addition on the magnetic properties and the microstructure of Nd-Fe-B thin films which were produced by a conventional rf sputtering method. It was found that the addition of Cr to the Nd-Fe-B thin film is very effective in enhancing the remanence and the coercive force measured in the direction perpendicular to the film plane. A high coercive force (Hc=9.5 kOe) was achieved at the following conditions: the Cr addition of 8.6 at.%, the Nd-Fe-B thickness of 300 nm and the Cr underlayer thickness of 50 nm. From the TEM observation, a columnar structure, consisting of the Nd2Fe14B compound and an amorphous phase is observed to exist. The main phase is Nd2Fe14B, whose tetragonal c-axis is highly aligned in the direction perpendicular to the film plane. The improvement of the reduced remanence and the coercive force can be attributed to the modification of the c-axis aligned Nd2Fe14B columnar structure. (orig.)