Effect of boron addition on disorder-order transformation of FePt thin films

The MgO20nm/(FePt0.85B0.15)(x nm)/MgO20 (nm) (x = 10 and 50) films were prepared on Si (1 0 0) substrates by RF magnetron sputtering. The boron content in thin. lms was found to be about 15 at% by wavelength dispersive spectroscopy. At 50 nm of film thickness, the coercivity of Fe0.5Pt0.5 and (FePt)(0.85)B-0.15 films increased drastically above 400 degrees C. Measured lattice constants and coercivity indicated that addition of boron to the FePt. lm at 50 nm thickness is not effective in reducing the ordering temperature. However, in case of 10-nm-thick films, addition of boron decreased the ordering temperature to 400 degrees C, which is 200 degrees C lower than that of the film without boron. Decrease of the ordering temperature is attributed (closely related) to the high diffusivities of Fe and Pt associated with the defects by movement of the boron atoms to interstitial or substitutional lattice site. (C) 2006 Elsevier B. V. All rights reserved.