Magnetic properties of NdFeB thin films on platinum underlayers

A series of NdFeB (Nd₁₂Fe₈₂B₆) films of different thicknesses were r.f. sputtered on 1000 Å-thick Pt underlayers for information storage application. The perpendicular coercivity has a maximum of 3000 Oe for a 1000 Å - thick film annealed at 625°C for fifteen minutes. By using Transmission Electron Microscopy (TEM) we have found that the film is tetragonal with an additional fcc structure. The crystallographic texture is established during annealing at 625°C. The TEM micrographs show some voids and a grain size in the range 30 to 50 nm. For films annealed at 700°C for fifteen minutes, the voids disappeared and the grain size was found to be 100 nm. X-Ray Diffraction analysis of the annealed sample indicates that the NdFeB film is amorphous. Annealing at 625°C produces the 2:15:1 phase in the films