Enhanced magnetic properties of Nd-Fe-B thin films crystallized by heat treatment

Nd2Fe14B Phi phase crystallites were formed in Nd16.7Fe65.5B17.8 thin films prepared by RF sputtering with subsequent heat treatment. The 2 mum-thick films were deposited onto 0.1 mm Mo sheets at an average substrate temperature (T-s) of 365degreesC. The enhanced magnetic properties of the magnetically anisotropic thin films were investigated using different heating rates (h(r)) of 10degreesC, 20degreesC, 50degreesC and 100degreesC/min in an annealing experiment. Transformation from the amorphous phase to the crystalline phase is clearly manifested by the formation of fine crystallites, embedded as a columnar matrix of Nd2Fe14B phase. High-resolution scanning electron microscope data of the cross-section of the annealed films show columnar stacking of Nd2Fe14B crystallites with sizes <500 nm. Transmission electron microscope observations revealed that the microstructure of these films having out-of-plane magnetization consists of uniformly distributed Phi phase with grain size around 400 nm together with small Nd rich particles. This grain size of Phi phase is comparable to the single domain particle diameter of Nd2Fe14B. Significant change in H-i(c), 4piM(rperpendicular to) and 4piM(rperpendicular to) with h(r) was confirmed. Annealing conditions with a heating rate of 50degreesC/min to an annealing temperature (T-a) of 650degreesC for 30 min was consequently found to give optimum properties for the NdFeB thin films. The resulting magnetic properties, considered to be the effect of varying h(r) were H-i(c) = 1307-1357 kA/m, 4piM(rperpendicular to) = 0.78-1.06 T and 4piM(sperpendicular to) = 0.81-1.07 T. (C) 2002 Elsevier Science B.V. All rights reserved.