Paper NT+AS+MI-WeM9
Study of L1₀ Ordering in ⁵⁷Fe/Pt Multilayers

Wednesday, November 2, 2011, 10:40 am, Room 207

Ordered L1₀ FePt, FePd and CoPt alloy thin films have large magnetic anisotropy constants suitable for high-density recording media. The L1₀ ordered phase is obtained with post growth annealing at high temperatures. However, the high temperature annealing leads to grain growth. The present work is an attempt to lower the transition temperature starting with multilayer precursors. The evolution of the structural and magnetic properties of Si(sub) [⁵⁷Fe(19Å

)/Pt (25Å)]_x10 multilayers as a function of vacuum annealing at different temperatures is studied. The film thickness is selected to have equi-atomic stoichiometry. The multilayers are prepared by ion beam sputtering. X-ray reflectivity (XRR), X-ray diffraction (XRD), and magneto optical Kerr effect (MOKE) and conversion electron Mössbauer spectroscopy (CEMS) are used to characterise the as-deposited and annealed multilayers. Using XRR it is observed that due to intermixing FePt alloy formation takes place with annealing. The XRD indicated the presence of superstructure peaks at 350⁰C and above.Mössbauer measurements indicated a clear evidence for the strong exchange coupling between the soft fcc FePt and hard fct FePt phase. The results indicate that the multilayer structure does not transform directly to the ordered fct FePt, rather first an fcc FePt phase is formed and subsequently it gets converted in to the fct FePt phase as a function of annealing. A detailed study on stoichiometric FePt system embedded in Carbon matrix prepared by ion beam sputtering technique will also be discussed.

Few preliminary results of polarised neutron reflectivity measurements on FePt/FeNi exchange spring magnets will be discussed.