Search

We report electron transport mechanism in FePt-C granular films as a function of temperature by varying intergranular separation. FePt-C nanogranular films were prepared by sputtering on MgO substrates. From magnetic measurement of the sample, a coercivity of about 3T was found in the perpendicular direction. Above 25 K, the electrical resistivity of the films were found to obey Mott variable range hopping, Efros-Shklovskii variable range hopping and extended critical regime depending on the intergranular separation. However, at lower temperatures it deviates from the above behaviour showing an increase in conductance. Reduced activation energy calculated from resistivity data of these films shows metal-insulator transition. The metallic nature observed at low temperature was attributed to the intergranular ferromagnetic type ordering between granules that enhances the transport of electrons. Intergranular separation, thus, can be used as a tool to engineer the electron transport mechanism to different hopping regimes or extended critical regime in these films.

The spin injection efficiencies in epitaxial Co2MnSi (CMS)/Pt thin films were investigated in spin pumping configuration. The inverse spin Hall (effect) voltage significantly depends on the post-annealing temperature Ta of CMS, which shows one order larger values than those of Fe and CoFe at Ta = 400 °C. The effective spin mixing conductance derived by the analytical model reaches 6.5 × 1019 m−2. Our findings suggest that the Co-based Heusler alloys could be promising material candidates as the spin injection source with spin pumping.

Although magnetostriction is universal in magnetic materials, understanding its microscopic origin remains challenging. Here the authors use X-ray and ultrafast electron diffraction to separate the material’s sub-picosecond spin and lattice responses and reveal the magnetoelastic stress generated by demagnetization.

“The technical support from SLAC Accelerator Directorate, Technology Innovation Directorate, LCLS laser division and Test Facility Division is gratefully acknowledged. We thank S.P. Weathersby, R.K. Jobe, D. McCormick, A. Mitra, S. Carron and J. Corbett for their invaluable help and technical assistance. Research at SLAC was supported through the SIMES Institute which like the LCLS and SSRL user facilities is funded by the Office of Basic Energy Sciences of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515. The UED work was performed at SLAC MeV-UED, which is supported in part by the DOE BES SUF Division Accelerator & Detector R&D program, the LCLS Facility, and SLAC under contract Nos. DE-AC02-05-CH11231 and DE-AC02-76SF00515. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.” and “Work at BNL was supported by DOE BES Materials Science and Engineering Division under Contract No: DE-AC02-98CH10886. J.C. would like to acknowledge the support from National Science Foundation Grant No. 1207252. E.E.F. would like to acknowledge support from the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES) under Award No. DE-SC0003678.” This has been corrected in both the PDF and HTML versions of the Article.

In order to optimize the nanogranular structure of FePt-C for heat-assisted magnetic recording media, we investigated the influence of MgO underlayers on the growth of FePt grains in the FePt-C layer. The FePt-C layer was deposited by using the alternating sputtering method, by which FePt and FePt-C layers were alternately deposited. To understand the growth mechanism of the FePt-C layer on the MgO underlayers deposited under various conditions, detailed plan-view and cross sectional transmission electron microscopy observations were made for different film thicknesses. We found that columnar FePt grains grow only when the deposition conditions of the MgO underlayer are optimal. Direct TEM observation of the growth process of the FePt-C layer revealed that the number density of nuclei is sufficient in the initial stage of the film deposition; however, coarsening of the grains after grain impingement causes a substantial decrease in the number density of the FePt grains.

A detailed study of the Fe2 − xCoxMnSi (0 ≤ x ≤ 0.6) alloys has been carried out by investigating the samples by x-ray diffraction, Mössbauer spectroscopy, magnetization, transport and current spin polarization measurements. A perfectly ordered L21 phase is found to exist for x = 0.4. Competing magnetic interactions between ferromagnetic and antiferromagnetic (AFM) phases are seen in the alloys with x < 0.2, whereas the AFM phase is completely absent for x ≥ 0.2 as revealed by the magnetization and resistivity data. The Curie temperature and saturation magnetization values increase with increase in the Co concentration. Anomalous, non metallic-like behaviour is observed for x = 0.4. Current spin polarization values of 0.61  ±  0.01 and 0.66  ±  0.01 were deduced for x = 0.2 and x = 0.4 respectively, using the point contact Andreev reflection spectroscopy . Considering the high spin polarization and Curie temperature, materials with x ≥ 0.2 appear to be very promising for spintronic devices. [ABSTRACT FROM AUTHOR]