Increase in coercivity of Fe-Pt thin film permanent magnets by N2+ ion implantation and heat treatment in hydrogen gas

We investigated Fe-Pt thin films implanted with nitrogen ions followed by heat treatment under a vacuum at 650 degrees C and further treatment in hydrogen gas of 0.1 atm at 350 degrees C. The elemental composition of the Fe-Pt films is Fe54Pt46, and the thickness of the films is 110 nm. Energies of the implanted N-2(+) ions are 120 or 130 keV. In-plane and out-of-plane coercivities of the Fe-Pt films after the heat treatment at 650 degrees C without the N-2(+) ion implantation are 9.8 and 7.7 kOe, respectively. The in-plane coercivity for an implanted N dose of 3.5 x 10(17)atoms/cm(2) increases to 13.3 kOe after the heat treatment at 650 degrees C under a vacuum and increases to 15.4 kOe after the heat treatment at 350 degrees C in hydrogen gas. The out-of-plane coercivity for the same dose increases to 12.7 and 14.4 kOe after these heat treatments, respectively. Backscattering Spectrometry with 6.0 MeV He-4 ions indicates that the implanted nitrogen atoms are not released but stay in the films and that the amount of the nitrogen atoms decreases below a detection limit after the heat treatment at 650 degrees C. Widths of FePt (1 1 1) peaks in X-ray diffraction patterns indicate that the size of the FePt crystallites decreases with increasing the dose of nitrogen after the heat treatment at 650 degrees C and that the size remains unchanged by the heat treatment at 350 degrees C in hydrogen gas. (C) 2011 Elsevier B.V. All rights reserved.