PREPARATION AND CHARACTERIZATION OF Nd-Fe-B FILMS WITH HIGH COERCIVITY

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In order to develop thin film permanent magnet (TFPM) necessary for miro- or nanb-devices, preparation and characterization of Nd-Fe-B films with very high coercivity have been investigated. As the high coercivity is the most important material requisite for TFPM, we concentrated to find target composition which may result high coercivity. We prepared the films by RF-sputtering with subsequent heat treatment. As-deposited films were in amorphous state and magnetically very soft with strong in-plane magnetic anisotropy. We found that some of the as-deposited films prepared under special conditions have very weak out-of-plane anisotropy. In those films heat treated under appropriate conditions, Nd_2Fe_<14>B phase crystallizes with c-axis oriented along the film normal. We named such a phenomenon as self-texturing crystal growth.As the c-axis is magnetic easy direction, the film is easily magnetized perpendicular to the film plane. The films show prominent permanent magnet characteristics: coercivity higher than 15kOe, residual flux density of 9kG, and maximum energy product (BH)_<max> as high as 20.1MGOe. Such a high coercivity may be resulted from Nd_2Fe_<14>B crystallites of which size is as large as single domain size and c-axis is orienting along film normal. We consider that such a fine crystallite size maybe in relation with nucleation density in self-texturing crystal growth.