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We estimated the magnetic damping constant a of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While a increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principles calculations, we attributed the origin of the large a in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings of their spins. [ABSTRACT FROM AUTHOR] more...

We investigated the structure and magneto-transport properties of magnetic junctions using a Co2Fe(Ga0.5Ge0.5) Heusler alloy as ferromagnetic electrodes and a Cu(In0.8Ga0.2)Se2 (CIGS) semiconductor as spacers. Owing to the semiconducting nature of the CIGS spacer, large magnetoresistance (MR) ratios of 40% at room temperature and 100% at 8 K were obtained for low resistance-area product (RA) values between 0.3 and 3 Ωµm2. Transmission electron microscopy observations confirmed the fully epitaxial growth of the chalcopyrite CIGS layer, and the temperature dependence of RA indicated that the large MR was due to spin dependent tunneling. [ABSTRACT FROM AUTHOR] more...

The non-local spin signals of Co2Fe(Ga0.5Ge0.5)/Cu lateral spin valves with sub-micron size dimensions were measured with varying temperatures. The non-local spin signal reaches 54mX at 4K, while it degrades down to 13mΩ at room temperature. Analysis based on the one-dimensional spin diffusion model clarifies the dominant source for degrading of the spin signal is suppression of the spin diffusion length in Cu, not the spin polarization, indicating Co2Fe(Ga0.5Ge0.5) keeps half-metallic nature even at room temperature. The temperature dependence of non-local spin signal was found to exhibit a downturn at 36 K. The presence of magnetic impurities, detrimental effect of which becomes more pronounced for diffusive transport in long Cu wires, is suggested to cause the observed downturn in non-local spin signals. [ABSTRACT FROM AUTHOR] more...

The spin Hall angle of Pt in Co75Fe25/Pt bilayer films was experimentally investigated by means of the spin-torque ferromagnetic resonance and the modulation of damping measurements. By comparing the present results with the Ni80Fe20/Pt system, we found that the ferromagnetic layer underneath the Pt one greatly affects the estimation of the spin Hall angle. We also discuss the spin diffusion length of Pt and the ferromagnetic thickness dependence of the Gilbert damping coefficient. [ABSTRACT FROM AUTHOR] more...

We report the transport properties of a current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device with Co2Fe(Al0.5Si0.5ipt>) (CFAS) Heusler alloy ferromagnetic layers and a Ag spacer layer. The CPP-GMR devices showed relatively high ΔRA values and MR ratios up to 17 m Ω μm2 and 80% at 14 K, and 8 m Ω μm2 and 34% at 290 K. The spin diffusion length ∼3 nm and the bulk spin asymmetry ∼0.77 for the CFAS alloy at 14 K were estimated by the Valet–Fert model, indicating a large contribution of the interfacial scattering. [ABSTRACT FROM AUTHOR] more...

Co2MnSi/Cr/Co2MnSi (001)-fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices were fabricated via an UHV magnetron sputtering system. The relationship between the degree of chemical ordering in Co2MnSi (CMS) and the CPP-GMR characteristics was investigated systematically against the annealing temperature of the devices. X-ray diffraction profiles and reflection high-energy electron diffraction images indicated that annealing improved L21-ordering. The MR ratio also increased upon annealing and the maximum MR ratio of 5.2% and ΔRA of 6.5 mΩ μm2 were achieved by annealing at 400 °C. These results indicate that promoting the degree of L21-ordering in CMS enhances the bulk and/or interface spin-asymmetry coefficients. [ABSTRACT FROM AUTHOR] more...

Interlayer exchange coupling (IEC) in trilayers, which consist of a full Heusler Co2MnSi (CMS) phase as ferromagnetic layers separated by a Cr spacer layer, has been investigated. The shape of magnetization loops shows unusual oscillatory behavior with the thickness of Cr. The oscillation period is about 3.3–3.5 nm. The charecteristics of magnetization curves show that 90° coupling plays a dominant role in IEC between CMS layers. Moreover, the strength of 90° coupling turns out to be very high (up to -1.85 ergs/cm2) around the first oscillation peak. [ABSTRACT FROM AUTHOR] more...

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of the multilayer thin film using a full-Heusler Co2MnSi (CMS) phase as ferromagnetic electrodes has been investigated. A multilayer of Cr buffer (10 nm)/CMS (50 nm)/Cr spacer (3 nm)/CMS (10 nm)/Cr cap (3 nm) was grown on a MgO(100) substrate. The 50 nm thick CMS layer which was deposited on the Cr buffer at 573 K was epitaxially grown and had an L21 structure. The resistance change-area product (ΔRA) at room temperature was 19 mΩ μm2, which is one order of magnitude larger than those in previously reported trilayer systems, resulting in the MR ratio of 2.4%. A possible origin of the enhanced ΔRA is considered to be the large spin polarization in a high-quality L21 CMS film. [ABSTRACT FROM AUTHOR] more...

Current-induced magnetization reversal of perpendicularly magnetized layers was studied in current-perpendicular-to-plane giant magnetoresistance pillars with L10-FePt (001) layers. The FePt layers exhibited strong perpendicular magnetic anisotropy of the order of 107 erg/cm3. A series of magnetoresistance curves after applying pulse currents with different current densities showed that current-induced magnetization reversal from an antiparallel to a parallel alignment occurred at the current density of the order of 108 A/cm2 with the assistance of magnetic field. [ABSTRACT FROM AUTHOR] more...

Fe/MgO/Fe nanoparticles/MgO/Co double tunnel junctions were prepared by molecular beam epitaxy for current-perpendicular-to-plane transport measurements on submicrometer-sized pillars. Microstructural observations indicate that the samples exhibit a fully epitaxial layered structure with sharp and flat interfaces including well-defined separated Fe nanoparticles between the barriers. The introduction of asymmetric MgO tunnel barriers, i.e., with different thicknesses, in the double junction leads to a clear observation of Coulomb staircase and associated tunnel magnetoresistance oscillations. An estimation of the capacitance of the system indicates that these transport phenomena are due to charging effects of the magnetic particles. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

L1[sub 0] ordered FePt alloy films with large magnetic anisotropy have been successfully prepared by alternating Fe(001) and Pt(001) monatomic layers on MgO (001) substrates at low temperatures below 230 °C. In addition to the fundamental (002) peak, (001) and (003) superlattice peaks have clearly been observed in the x-ray diffraction patterns for all the samples, indicating the formation of L1[sub 0] ordered structure. The magnetization measurements show that all the samples are perpendicularly magnetized. Large uniaxial magnetic anisotropy (K[sub u]=3.0×10[sup 7] erg/cc) and high chemical ordering (long-range order parameter S=0.7±0.1) have been obtained even at the substrate temperature T[sub s]=200 °C. The magnetization curves show good magnetic squareness (Mr/Ms∼0.9) for the samples grown at T[sub s]>=160 °C. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

Investigates the artificial fabrication of an L1[sub 0]-type ordered FeAu alloy by alternate monatomic deposition. Details of the thin film preparation techniques; Examination of the fabrication method of ordered alloys with layered structure; Description of the Fe-Au system. more...