No abstract

The influence of Cu, Ag, and Au additives on the L1 0 ordering, texture, and grain size of FePt thin films has been examined. Lattice parameter data indicated that Au and Ag additives tended to segregate from FePt, but Cu alloyed with FePt. FePt films with Au or Ag additive showed 1-2 kOe higher coercivity values compared to a pure FePt film after annealing at 450°C and above for 10 min. The addition of at least 20 vol. % Cu to FePt boosted average coercivity values and increased ͑001͒/͑002͒ x-ray peak intensity ratios, suggesting an accelerated L1 0 ordering process for annealing temperatures exceeding 350°C. Decreasing the film thickness promoted ͑001͒ film texture in FePtϩ20% Cu films, but higher annealing temperatures were required to achieve large coercivity. Au and Ag limited the average grain size compared to a pure FePt film. Cu additive increased the average grain size and film roughness.

Anomalous metamagnetic-like transition in a FeRh/Fe3Pt interface occurring at T ≈ 120 K in the field-cooledcooling curves for low magnetic fields AIP Advances 2, 032168 (2012) Electric-field-control of magnetic anisotropy of Co0.6Fe0.2B0.2/oxide stacks using reduced voltage J. Appl. Phys. 112, 033919 (2012) Observation of intriguing exchange bias in BiFeO3 thin films J. Appl. Phys. 112, 033915 (2012) Rotary transportation of magnetic nanoparticle chains on magnetic thin film array

Room-temperature x-ray diffraction and Mössbauer effect techniques have been used to characterize the structural features and local atomic environments of sputtered Fe51Pt49 thin films following various isothermal treatments. Both techniques show that no significant changes occur in the chemically ordered L10 tetragonal phase after it has formed. In contrast, changes in the disordered face-centered-cubic (fcc) phase are observed prior to the transformation into the ordered tetragonal phase. Mössbauer measurements indicate the development of increasing short-range order in the disordered fcc phase with increasing annealing temperature. Asymmetries in the fcc x-ray diffraction profiles also suggest the presence of lattice distortions caused by atomic size differences commonly found in the quenched disordered fcc phase of materials that form ordered structures. Quasi-real-time kinetic measurements of the disorder→order transformation in sputtered Fe51Pt49 thin films within the temperature range 300 °C⩽T⩽400 °C have also been conducted using high-temperature x-ray diffraction techniques. Significant differences are observed between the kinetic parameters determined in this study and those of previous reports. It is proposed that these differences arise from the lower temperature range investigated in the present work, where the gradual changes occurring in the fcc phase can influence the rate of the ordering transformation. Furthermore, because the initial state of disorder in Fe∼50Pt∼50 films can be influenced by the deposition conditions, variability in the low-temperature ordering kinetics should be expected among Fe∼50Pt∼50 films prepared under different conditions.

We identified reactively sputtered HfO2 as a particularly good material for making thin insulating barriers for spin-dependent tunnel junctions. This material allows one to form pinhole-free tunnel barriers with good transmission of the spin polarization of the tunneling electrons. Magnetic tunnel junctions consisting of a thin layer of HfO2 sandwiched between transition metal electrodes (Co and Fe, for instance) exhibit changes of tunnel resistance up to 30% at low temperature as a function of applied field. This effect can be used in a variety of magnetic field sensing applications or in magnetic random access memory.