Solid State Phenomena Vols. 124-126

Abstract: We review our recent experimental findings by optical orientation spectroscopy that show efficient spin relaxation within semiconductor spin detectors to be an important factor limiting efficiency of spin injection in spin light-emitting structures based on ZnCdSe/ZnMnSe and InGaN/GaMnN. We provide evidence for the physical mechanism responsible for the observed efficient spin relaxation that accompanies momentum and energy relaxation of excitons/carriers. These findings call for increasing efforts in suppressing spin relaxation in spin detectors.

Abstract: We analyze the effect of the geometrical shape and size of the cross section on the spin-polarized transport and the giant magnetoresistance (GMR) by a finite element method, and evaluate the stability and the physical properties of nano-scale spin valves. We calculate the transmission coefficients in the ballistic regime by using a transfer-matrix method, and evaluate the GMR of the current perpendicular to the plane (CPP) by using a circuit theory. The conduction-band structure is simplified to the potential step, which is determined by combining the interfacial parameters calculated by first-principles with the free electron model. The geometrical shapes of the cross section are line and square. As a result, the cross sectional shape has a significant effect on the spin-polarized transport and the GMR. The square-shaped cross section has an advantage of the large GMR, which is contrary to the line-shaped cross section. These phenomena result from the difference of the cut-off energies with the transverse modes and, consequently, the different spin-down transmission coefficients.

Abstract: First principle calculations were performed on the electronic and magnetic structures of the transition metals doped GaN. Seven elements in 3d transition metals from V to Cu were used as a dopant. Magnetic phase was stable compared to non-magnetic phase for all transition metals doped GaN. Total magnetic moments followed Hund’s rule to maximize the magnetic moment. Transition element projected magnetic moments showed that most of magnetic moments were concentrated on transition metals in the cases of V, Cr, and Mn doped GaN, which could not be used for DMS. Since Fe and Ni doped GaNs are intrinsic insulators, Fe and Ni doped GaNs could not be used for DMS materials unless additional dopants are introduced. The most probable candidates for DMS applications were predicted to be Co or Cu doped GaNs, respectively.

Abstract: Structural and microwave properties of Fe-based nanoalloy powders, mechanochemically synthesized with a composition corresponding to Finemet (Fe73.5Si13.5B9Nb3Cu1), were investigated. The nanopowders, dominated by bcc-Fe (Si), consist of nanocrystallites and display high magnetization with low-coercivity. The microwave measurements show that the nanocomposites comprising the nanopowders possess high, broadband magnetic permeability.

Abstract: Oriented and densely dispersed L10-FePtCu nanoparticles have been directly synthesized by co-evaporation of Fe, Pt and Cu using rf-magnetron sputtering onto NaCl substrate kept at 563-613K without any post-deposition annealing. Under as low a substrate temperature as 563K, superlattice reflections of the L10 phase appeared in selected area electron diffraction pattern, while the intensity was quite weak. As the substrate temperature increased from 563K to 613K, <100> oriented growth as well as the atomic ordering were promoted, resulted in a large increase of coercivity.

Abstract: Sm2Fe17Nx film magnets were prepared using a Sm2Fe17 target in a N2 gas atmosphere using a RF magnetron sputtering technique. The effect of nitrogenation treatment such as N2 gas pressure during sputtering, film heating temperature, N2 gas rate, and the effect of film thickness on the microstructure and magnetic properties of Sm2Fe17Nx films were studied. Optimized magnetic properties with film thickness 270Å, N2 gas rate 10 % and heating temperature 530°C could be obtained. In-plane anisotropy, which was the basic goal in this study, was achieved by controlling the nitrogenation parameters.

Abstract: Yttrium aluminum garnet (YAG) nanoparticles of 14.5±3.2 nm in diameter are synthesized from yttrium acetate and aluminum isopropoxide in 1,4-butanediol by autoclave treatment at 300oC for 2h. Yttrium iron garnet (YIG) / YAG composite nanoparticles of 21.1±4.9 nm in diameter are synthesized from yttrium acetate and iron(III) acetylacetonate in 1,4-butanediol by autoclave treatment at 300oC for 2h using YAG nanoparticles as the seed. In contrast, YIG is not formed by the same procedure in the absence of the YAG seed. The saturation magnetizations of nanoparticles with different YIG/YAG ratios range from 11.9 to 17.8 emu/g. YIG/YAG nanoparticles dispersed in the agarose gel are observed by magnetic resonance imaging (MRI). The degree of the negative MRI contrast depends on the concentration of YIG/YAG nanoparticles.

Abstract: Ni(60Å)/Cu film possessing perpendicular magnetic anisotropy (PMA) changes its easy direction into the plane by ion irradiation, due to the relaxation of the strain. By fixing our eyes upon this magnetic property, the magnetic patterning of Ni(60Å)/Cu film using 40 keV O ion irradiation was performed through the photo-resist (PR) mask having 10㎛ x 10 ㎛pattern sizes to pattern the magnetic film. After the PR mask removal of an irradiated film, the magnetic properties were investigated by the magneto-optic Kerr effect and the formation of magnetic pattern was observed by the magnetic force microscopy. The PMA magnetic patterning of epitaxial Ni/Cu film was successfully performed in scale of ㎛ by using ion irradiation, compatible with device process.

Abstract: A novel excellent response of giant magnetoimpedance effect was found out in a magnetic LC-resonator consisting of a glass-coated amorphous Co83.2B3.3Si5.9Mn7.6 microwire and two capacitive cylindrical electrodes at the end of the microwire. The shapes of the impedance curves plotted vs. applied external dc-field varied dramatically with increasing frequency. The phase angle was also strongly found to be dependent on this field. The impedance curves were changing abruptly at near the resonance frequency. Because the permeability of ultra soft magnetic microwire is changing rapidly as a function of external magnetic field, the resonance frequency as well as impedance of the LC-resonator also changes drastically with respect to the external magnetic field. The maximum magnetoimpedance ratio value was reached as much as 1,600%. The sudden changes of phase angle as much as 180 degree evidenced the occurrence of resonance phenomenon. These results are promising for developing ultra-high sensitive magnetic sensor applications.