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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 polarization ( P ) of ferromagnetic Heusler alloys, Co 2 Fe(Ga x Ge 1− x ) ( x = 0, 0.25, 0.5, 0.75, and 1), is investigated by point contact Andreev reflection (PCAR) measurements. While the P values of the ternary Co 2 FeGe and Co 2 FeGa alloys are 0.58 and 0.59, respectively, the corresponding value for Co 2 Fe(Ge 0.5 Ga 0.25 ) is as high as 0.69. Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy shows a strong tendency for L2 1 ordering and a high Curie temperature of 807 °C. Ab initio calculations indicate that the band structures of the Co 2 FeGe and Co 2 Fe(Ge 0.5 Ga 0.5 ) alloys with L2 1 or B2 structures are half-metallic. Thin films of the quaternary Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy grown on MgO(0 0 1) substrates order to the L2 1 structure upon annealing at 500 °C, giving rise to a high P of 0.75. This is the highest P value reported for Heusler alloy thin films using the PCAR technique. Ferromagnetic resonance measurements show that the Gilbert damping constant of the film is ∼0.008. All these indicate that the Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy is promising as a spin polarized current source for spintronics devices.

Point contact Andreev reflection measurements of Co2MnSn1−xGax alloys showed that the spin polarization of L21 ordered quaternary Co2MnSn0.5Ga0.5 compound increased to 0.72 compared to 0.6 for Co2MnSn and Co2MnGa ternary alloys. The L21 Co2MnSn0.5Ga0.5 phase was found to be an intermetallic compound, in which the L21 structure was stable up to the melting temperature. The increase in spin polarization was attributed to the high degree of L21 order as well as an increase in the spin-up density of states near the Fermi level.

A detailed study of the Fe2-xCoxMnSi (0 = 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.

Spin gapless semiconductors (SGS) form a new class of magnetic semiconductors, which has a band gap for one spin sub band and zero band gap for the other, and thus are useful for tunable spin transport based applications. In this paper, we report the first experimental evidence for spin gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is also confirmed by first principles band structure calculations. The most stable configuration obtained by the theoretical calculation is verified by experiment. The alloy is found to crystallize in the cubic Heusler structure (LiMgPdSn type) with some amount of disorder and has a saturation magnetization of 3.7 Bohr's magneton/f.u.. and Curie temperature of 620 K. The saturation magnetization is found to follow the Slater-Pauling behavior, one of the prerequisites for SGS. Nearly temperature-independent carrier concentration and electrical conductivity is observed from 5 to 300 K. An anomalous Hall coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection data has yielded the current spin polarization value of 0.64, which is found to be robust against the structural disorder. All these properties are quite promising for the spintronic applications such as spin injection and can bridge a gap between the contrasting behavior of half-metallic ferromagnets and semiconductors., 14 pages, 7 figures, regular article

The interplay of light and magnetism has been a topic of interest since the original observations of Faraday and Kerr where magnetic materials affect the light polarization. While these effects have historically been exploited to use light as a probe of magnetic materials there is increasing research on using polarized light to alter or manipulate magnetism. For instance deterministic magnetic switching without any applied magnetic fields using laser pulses of the circular polarized light has been observed for specific ferrimagnetic materials. Here we demonstrate, for the first time, optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording. Our finding shows that optical control of magnetic materials is a much more general phenomenon than previously assumed. These results challenge the current theoretical understanding and will have a major impact on data memory and storage industries via the integration of optical control of ferromagnetic bits., Comment: 21 pages, 11 figures

The orientation dependence of current-perpendicular-to-plane giant-magnetoresistance (CPP-GMR) was investigated by fabricating ⟨001⟩ textured polycrystalline pseudo spin valves (PSVs) with Co2Fe(Ga0.5Ge0.5) (CFGG) Heusler alloy ferromagnetic layers and a Ag spacer. The PSV with 10 nm CFGG annealed at 400 °C exhibited the resistance-change area product (ΔRA) of 5.8 mΩ (MR ratio of 16%), the largest value reported for polycrystalline CPP-(P)SVs. The ⟨001⟩ textured CFGG PSV outperforms the ⟨011⟩ textured CFGG PSV possibly due to the reduced lattice mismatch or improved band matching at the CFGG/Ag interface.

We have investigated the structure and magnetoresistance of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs) using Co2Mn(Ga0.25Ge0.75) (CMGG) Heusler alloy ferromagnetic layers annealed at different temperatures. Relatively large ΔRA of 6.1 mΩμm2 and MR ratio of 40.2% were obtained in the CPP-PSV annealed at 400 °C. Annealing at higher than 400 °C led to a significant deterioration of MR outputs. Detailed structure analysis using transmission electron microscopy, three-dimensional atom probe, and synchrotron x-ray diffraction showed that the degradation of MR in the over-annealed sample was due to the increase of DO3 disorder in the CMGG layer, while the layered structure of the film is fully preserved.

Current-perpendicular-to-plane spin valves (SVs) with a new Heusler alloy of Co2Mn(Ga0.5Sn0.5) (CMGS) as magnetic layers and an Ag spacer have been investigated. Magnetoresistance (MR) values of 8.8% and 17.2% and resistance change-area product (ΔRA) of 4.0 mΩ μm2 and 6.5 mΩ μm2 were measured at 300 K and 12 K, respectively. Transmission electron microscopy observations have revealed that the CMGS magnetic layer was ordered to the B2 structure for the SV annealed at 400 °C. Higher annealing temperature led to the degradation of the multilayer structure, resulting in lower MR and ΔRA values regardless of the L21 structure of the CMGS layer. This suggests that MR properties may be enhanced further if the thermal stability of the multilayer structure is improved.