Hard magnetic properties of rapidly annealed NdFeB thin films on Nb and V buffer layers

NdFeB thin films of the form A (20 nm)/NdFeB(d nm)/A(20 nm), where d ranges from 54 to 540 nm and the buffer layer A is Nb or V were prepared on a Si( 100) substrate by magnetron sputtering. The hard Nd2Fe14B phase is formed b y a 30 s rapid anneal or a 20 min anneal. Average crystallite size ranged f rom 20 to 35 nm with the rapidly annealed samples having the smaller crysta llite size. These samples also exhibited a larger coercivity and energy pro duct than those treated by a 20 min vacuum anneal. A maximum coercivity of 26.3 kOe at room temperature was obtained for a Nb/NdFeB (180 nm)/Nb film a fter a rapid anneal at 725 degreesC. Initial magnetization curves indicate magnetization rotation rather than nucleation of reverse domains is importa nt in the magnetization process. A Brown's equation analysis of the coerciv ity as a function of temperature allowed us to compare the rapidly annealed and 20 min annealed samples. This analysis suggests that rapid annealing g ives higher quality crystalline grains than the 20 min annealed sample lead ing to the observed large coercivity in the rapidly annealed samples. (C) 2 001 Elsevier Science B.V. All rights reserved.