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

为了开发微纳米器件所需的薄膜永磁材料，本论文研究了高矫顽力Nd-Fe-B薄膜的制备和表征。由于高介电常数是制备薄膜晶体的最重要的材料要求，因此我们致力于寻找能够获得高介电常数的目标化合物。我们通过RF溅射和随后的热处理来制备薄膜。沉积态薄膜为非晶态，磁性非常软，具有很强的面内磁各向异性。我们发现，在某些特定条件下制备的沉积态薄膜具有很弱的面外各向异性。在适当的热处理条件下，Nd_2Fe_<14>B相以c轴沿着薄膜法线取向的方式结晶。由于c轴为易磁化方向，薄膜在垂直于薄膜平面的方向上易磁化，因此薄膜的自织构生长现象被称为自织构晶体生长。薄膜具有优异的永磁性能：矫顽力大于15 kOe，剩余磁通密度为9 kG，最大磁能积（BH）<max>高达20.1MGOe。这可能是由于Nd_2Fe_<14>B晶粒尺寸大到单畴尺寸，c轴沿沿着薄膜法线取向所致。我们认为这种细小的晶粒尺寸可能与自织构晶体生长中的成核密度有关。

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.