Coercitivity and its temperature dependence in NdFeB thin films with Cr, Mo, Ti, or Ta buffer layers

NdFeB thin films of the form A(20 nm)/NdFeB(d nm)/A(20 nm) were prepared by magnetron sputtering on a Si(100) substrate. The hard Nd2Fe14B phase is formed by a postanneal in vacuum. The buffer layers A used are Cr, Mo, Ta, Ti, and NdFeB layer thickness used are 540, 180, 90, and 54 nm. We have found several different combinations of anneal temperature, buffer layer, and NdFeB film thickness d that lead to large coercivity, as high as 17.0 kOe, and energy product, as high as 10.3 MG Oe. The temperature dependence of coercivity was analyzed using a modified Brown's equation and we find that the microstructural parameter alpha(K) and the effective demagnetization factor N-e change with the buffer material and anneal temperature. Possible magnetic reversal mechanisms are discussed in light of these results. (C) 2000 American Institute of Physics. [S0021-8979(00)51908-2].