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The mechanism of the enhancement of the current-perpendicular-to-the-plane giant magnetoresistance ratio (ΔR/R) by a Ag/In-Zn-O (IZO)/Zn spacer layer for the spin-valves with Co2(Mn0.6Fe0.4)Ge Heusler alloy ferromagnetic layers was investigated. The insertion of a thin Ag (0.2-0.6 nm) layer below the IZO layer was found to be critical for achieving relatively low resistance-area product (RA) ∼ 0.1 Ω μm2 and large ΔR/R up to 22%. Structural characterizations by scanning transmission electron microscopy revealed that the actual spacer layer was an inhomogeneous Ag-In:Mn-Zn-O nanocomposite, where the Ag-In is thought to play a role in current-confined-path (CCP) for electric current, and the Mn-Zn-O is an oxide matrix which forms by Mn diffusion from the Co2(Mn0.6Fe0.4)Ge layers and oxidation by In2O3 in IZO. The enhancement of ΔR/R is explained to be due to the current confinement through the Ag-In CCPs in the Ag-In:Mn-Zn-O nanocomposite spacer, and the lower RA values (0.065-0.011 Ω μm2) for the Ag-In:Mn-Zn-O CCP-spacer than those for the conventional Cu:AlOx CCP-spacer can be understood by assuming a lower resistivity in the Ag-In CCPs. [ABSTRACT FROM AUTHOR]

Nonmagnetic Cu2TiAl (CTA) Heusler compound is proposed as a new spacer material for all- Heusler alloy current-perpendicular-to-plane giant magnetoresistance devices based on firstprinciple calculations. The (001)-orientated Co2Mn(Ge0.75Ga0.25) (CMGG)/CTA/CMGG epitaxial pseudo spin valve (PSV) grown on MgO(100) single crystal substrate showed relatively large MR output, ΔRA ~ 5.4mΩµm2, which is comparable to that of the CMGG/Ag/CMGG PSV prepared with the same condition. Considering the short spin diffusion length in CTA, this result indicates a better electronic band matching for the CTA/CMGG interface than the Ag/CMGG interface in agreement with the first-principle calculation results. (001)- and (011)-orientated CMGG/CTA/CMGG PSV show similar MR outputs, indicating that the CTA spacer suppresses the orientation dependence of MR output which is usually observed in Ag-spacer CPP-PSV. [ABSTRACT FROM AUTHOR]

We fabricated (001)-oriented C1b-NiMnSb epitaxial films on MgO substrate by a magnetron sputtering system and systematically investigated the structure, magnetic property, and anisotropic magnetoresistance (AMR) effect. NiMnSb film was deposited using a stoichiometric NiMnSb target which has Mn-deficient (Mn ~ 28.7 at. %) off-stoichiometric composition ratio. We have investigated bulk spin-polarization in NiMnSb films by measuring AMR on the basis of recent study for half-metallic L21-Heusler compounds. Although the negative sign of AMR ratio, which is indicative of half-metallic nature, was observed in the single layer NiMnSb films, the magnitude of AMR ratio (-0.10% at RT) was about half of the largest value reported for half-metallic L21-Heusler compounds. The current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) devices of NiMnSb/Ag/NiMnSb show MR ratio of 13.2% at 10K and 4.2% at 300 K, which is higher than the previous result for NiMnSb/Cu/NiMnSb CPP-GMR devices [Caballero et al., J. Magn. Magn. Mater. 198-199, 55 (1999)], but much less than the CPP-GMR using L21-Heusler electrodes. The reduction of intrinsic bulk spin-polarization originating from the Mn-deficiency in NiMnSb layer is expected to be the main reason for small MR values. [ABSTRACT FROM AUTHOR]

Enhancement of magnetoresistance output was attained in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices by using a bcc CuZn alloy for the spacer. Pseudo spin valves that consisted of the Co2Fe(Ga0.5Ge0.5) Heusler alloy for ferromagnetic layers and CuZn alloy with the composition of Cu52.4Zn47.6 for a spacer showed the large change of the resistancearea products, ΔRA, up to 8 mΩ∙µm² for a low annealing temperature of 350 °C. The ΔRA value is one of the highest reported so far for the CPP-GMR devices for the low annealing temperature, which is essential for processing read heads for hard disk drives. We consider that the enhancement of ΔRA is produced from the spin-dependent resistance at the Co2Fe(Ga0.5Ge0.5)/CuZn interfaces. [ABSTRACT FROM AUTHOR]

We have experimentally investigated the crystal orientation dependence of band matching in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valves using Co2Fe(Ge0.5Ga0.5) (CFGG) Heusler alloy ferromagnetic layer and NiAl spacer. The high quality epitaxial CFGG/NiAl/CFGG all-B2-trilayers structure devices were fabricated on both MgO(001) and sapphire (1120) single crystal substrates to create (001) and (110) crystal orientations. Same magneto-transport properties were observed from these two differently orientated devices indicating that there is no or little orientation dependence of band matching on MR output. We also found that all-B2-trilayer structure was free of lattice matching influence depending on the crystal orientation, which made it a good candidate for CPP-GMR device. [ABSTRACT FROM AUTHOR]

The magnetoresistive (MR) properties of Co2Fe(Ge0.5Ga0.5) (CFGG) Heusler alloy-based currentperpendicular- to-plane giant magnetoresistance pseudo-spin-valves (PSVs) are investigated. The PSV films are epitaxially grown on a sapphire (11̄20) substrate with an Ag or Cu spacer layer, and their magnetoresistive properties are compared with those of PSV grown on MgO(001) substrates. For substrates with an Ag spacer, the PSV with the (001)[110]CFGG//(001)[010]Ag interface grown on MgO(001) exhibits a higher MR output compared with the (110)[001]CFGG//(111)[1̄10]Ag interface grown on sapphire (11̄20). In contrast, a higher MR output is obtained using a Cu spacer with the (110)[001]CFGG//(111)=1̄10]Cu interface. These results demonstrate that the MR outputs depend upon the crystal orientation at the interface, and that interfaces with a small misfit tend to exhibit a larger MR output. This indicates the influence of crystal orientation as well as lattice mismatch upon the interfacial spin scattering asymmetry. [ABSTRACT FROM AUTHOR]

A study was conducted to analyze the magnetic characteristics of nanosized magnetite made by coprecipitation and compare them against those determined by the microemulsion technique. Experimental results indicated differences between the samples that could be correlated with changes in the small strained crystals. In addition, the existence of a nonmagnetic layer may have been influenced by the canting of the surface spins.

We investigated the temperature dependence of magnetoresistive (MR) outputs of current-perpendicular-to-plane pseudo spin valves with Co2FeAl1-xSix (0 ≤ x ≤ 1) Heusler alloy ferromagnetic layers and a Ag spacer layer to optimize x. The MR ratios at room temperature do not show x dependence, while the MR ratios measured at 5 K showed strong x dependence; the largest resistance change-area product ΔRA = 21 mΩ·μm2 was obtained for x = 1 and ΔRA decreased with decreasing x. The results apparently contradicts with the theoretical prediction that the highest spin polarization is attained for x = 0.5. The discrepancy is due to the structural origin that the L21 order is obtained only in the Co2FeSi alloy film. [ABSTRACT FROM AUTHOR]

We have studied the structure and magnetoresistive properties of polycrystalline current-perpendicular-to-plane giant magnetoresistance pseudo spin-valves (PSVs) with Co2Mn(Ga0.25Ge0.75) (CMGG) ferromagnetic layers and a Ag spacer. With (110) textured CMGG thin films and (111) textured Ag spacer, the PSVs annealed at 350 °C with 2 nm CoFe buffer layers showed ΔRA of 3.7 mΩ μm2 and MR ratio of 12.2%, while the PSVs without the buffer layer showed ΔRA of only 1.3 mΩ μm2. High angle angular dark field images showed that the drop of ΔRA by annealing was due to the deterioration of the multi-layer CMGG/Ag/CMGG structure. Energy-dispersive X-ray spectroscopy images further confirmed the interdiffusion between CMGG layer and the Ag layer outside the CMGG/Ag/CMGG trilayer. In addition, we discuss the difference in the magnetoresistive properties of polycrystalline and epitaxial PSVs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetic properties of Fe particles, with the size around 2 rim, in granular Fe-Mg[F.sub.2] films were investigated by DC and AC magnetization measurements. Anomalous two cusps appeared in zero-field cooled magnetization and AC susceptibility against temperature. Large nonlinear susceptibility suggests the freezing of moments induced by magnetic interaction between particles. Index Terms - fine particle, non-linear susceptibility, superparamagnetism

Bi-quadratic interlayer exchange coupling is found below 100 K in a Co2MnSi/Ag/Co2MnSi current-perpendicular-to-plane pseudo spin valves. The bi-quadratic coupling constant J2 was estimated to be ∼-0.30 erg/cm2 at 5 K and the strong temperature dependence of the coupling strength points its likely origin to the 'loose spin' model. Application of current of ∼2 × 107 A/cm2 below 100 K leads to an increase in the magnetoresistance (MR), indicating current induced antiparallel alignment of the two magnetic layers. These results strongly suggest that the presence of the bi-quadratic interlayer exchange coupling causes the reduction of the magnetoresistance at low temperature and illustrates the importance of understanding the influence of interlayer exchange coupling on magnetization configuration in magnetic nanostructures. [ABSTRACT FROM AUTHOR]

We report broad bandwidth, 0.1-10 THz time-domain spectroscopy of linear and electro-optic polymers. The common THz optical component materials high-density polyethylene, polytetrafluoroethylene, polyimide (Kapton), and polyethylene cyclic olefin copolymer (Topas) were evaluated for broadband THz applications. Host polymers polymethyl methacrylate, polystyrene, and two types of amorphous polycarbonate were also examined for suitability as host for several important chromophores in guest-host electro-optic polymer composites for use as broadband THz emitters and sensors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report the structure and transport properties of current-perpendicular-to-plane spin valves (CPP SVs) with Co2FeAl0.5Si0.5 (CFAS) or Co2MnSi (CMS) Heusler alloy magnetic layers and an Ag or Cu spacer layer. A multilayer stack of sub/Cr/Ag/Heusler/(Ag or Cu)/ Heusler/Co75Fe25/Ir22Mn78/Ru was deposited on a MgO(001) single crystalline substrate by magnetron sputtering. Transmission electron microscopy observations showed epitaxial growth from the substrate to the top Heusler layer. The CPP SV with a CFAS/Ag/CFAS trilayer showed relatively large magnetoresistance (MR) ratios of 12% at room temperature and 31% at 12 K, with monotonous temperature dependence. However, the MR values of the SV with the CMS/Ag/CMS trilayer showed a different temperature dependence with a maximum value of 22% at 100 K. This might be related to the 90° couplings between the two CMS layers. [ABSTRACT FROM AUTHOR]

We have investigated the effect of Cr substitution for Fe on the spin polarization, P, of Co2CrxFe1-xSi alloys using the point contact Andreev reflection method. A steep increase from P=0.57 to P=0.64 occurs by a small substitution of Cr for Fe of x=0.02, thereafter P values are constant for higher Cr concentrations up to x=0.4. The increase in spin polarization can be attributed to both the improved L21 ordering found experimentally as well as the half-metallicity predicted by ab initio calculations in the composition range of 0≤x≤0.5. We propose the composition range of 0.02≤x≤0.1 is the most promising for ferromagnetic electrodes of magnetic tunneling junctions to achieve high tunneling magnetoresistance. [ABSTRACT FROM AUTHOR]

The article presents a complete study of the properties of the current- perpendicular-to-plane spin valves with a [Co.sub.2]Mn([Ga.sub.0.5][Sn.sub.0.5]) Heusler alloy. The magnetoresistance properties of the system are shown to be linearly dependent on the thermal stability of the multilayer structure.

Several studies are conducted to explain the structure, as well as the transport properties of the current-perpendicular-to-plane spin valves using [Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5] and [Co.sub.2]MnSi Heusler alloy electrodes. The valves are shown to exhibit extremely high magnetoresistance, which is then completely dependent on the temperature.

The current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) of a spin valve with [Co.sub.2]MnSi (CMS) Heusler alloy ferromagnetic electrodes is described. The studies have shown that the high spin polarization of the epitaxial CMS layers is the most likely origin of the high MR ratio.

Interlayer exchange couplings are examined for [Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5]/Cr/[Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5] trilayers films grown on MgO (001) single crystal and thermally oxidized Si substrates. Strong exchange couplings are observed for the films with the Cr spacer layer and the relationship of interlayer couplings with the structure is discussed.