Yujiro Nagata

Magnetism and transport properties of Hf1−xTaxFe2 and Mn2−xCrxSb

Abstract The magnetism and transport properties of Hf 1− x Ta x Fe 2 (0.1≤ x ≤0.2) and Mn 2− x Cr x Sb ( x =0.1) were studied. Hf 1− x Ta x Fe 2 ( x >0.15) has a successive magnetic transition from ferromagnetism to paramagnetism via antiferromagnetism at temperatures between 150 and 350 K, and the transition has a considerable effect on the transport property. In particular, a specimen with x =0.155 shows a metamagnetic transition near room temperature, and a significant magnetoresistance as large as 12% is observed in accordance with the metamagnetic transition. Mn 1.9 Cr 0.1 Sb, which has a first-order magnetic transition from antiferromagnetism to ferrimagnetism at about 300 K, also shows a field-induced magnetic transition at 300 K, and the transition strongly affects the transport property. A giant magnetoresistance as large as 30% was observed at about 300 K under an applied field of 20 kOe. The metamagnetic transition seems to give rise to giant magnetoresistance via s–d scattering.

CRYSTAL GROWTH AND MAGNETIC PROPERTIES OF SMFE2

SmFe2 crystals were grown by the self-flux method using Sm as a flux, and the crystallographic and magnetic properties of the crystal were studied for the first time. SmFe2 crystallizes in a cubic MgCu2-type structure (space group of Fd3m) with lattice constants of a=0.7425 nm. Saturation magnetization MS at 5 K and 300 K and the Curie temperature of SmFe2 are 64.4 emu/g, 59.8 emu/g, and 669 K, respectively. The easy-direction of the magnetization is parallel to the [110] direction of the cubic crystal at 300 K, but it changes to the [111] direction at about 195 K.

Magnetic properties of SmFe3 single crystal

SmFe3 single crystal was grown by a self-flux method using Sm as a flux, and its crystallographic and magnetic properties have been studied. SmFe3 crystalizes in the rhombohedral PuNi3-type structure and has lattice constants of a=0.5179 and c=2.4795 nm. The saturation magnetizations M S at 5 K and 300 K are respectively 89.9 emu/g and 80.7 emu/g, and the Curie temperature is 644 K. The anisotropy constants K1 and K2 at 5 K are -2.69×107 and 11.9×107 erg/cm3 and at 300 K are 2.36×107 and 2.21×107 erg/cm3. While the easy direction of magnetization is parallel to the c-axis at 300 K, it lies on the surface of a cone below 160 K. The angle θ between the c-axis and the generatrix of the cone is about 31° at 5 K.

Full Color Pixel with Vertical Stack of Individual Red, Green, and Blue Transparent Organic Light-Emitting Devices Based on Dye-Dispersed Poly(N-vinylcarbazole)

A organic light-emitting device (OLED) with the transparent electrodes has the specific feature of being transparent over the visible spectral range when light is not emitted. We can fabricate such a transparent device that emits red, green or blue light by choosing a light-emissive material for each color. Furthermore, This transparency enables us to fabricate a full color display by stacking these transparent red, green, and blue (RGB) devices. In this display, RGB lights are emitted from one pixel, each with controlled individual emissions of light. In our experimental device, white light with chromaticity coordinates (x,y) of (0.31,0.33) was obtained, when all the devices of a pixel were turned on. The average color rendering index (Ra) was 87.8.

Giant magnetoresistance observed in metamagnetic bulk-MnAu2

Abstract Giant magnetoresistance (GMR) Δϱ ϱ of about 10% was observed in bulk-MnAu 2 at 300 K in a field of 70 kOe. MnAu 2 is a tetragonal material with a spiral spin structure of Mn and shows a metamagnetic transition from a spiral to a ferromagnetic structure at an applied field of about 10 kOe at 300 K. Significant GMR was observed simultaneously with the metamagnetic transition.

Magnetic properties of Fe 2 O 3 -CaO-B 2 O 3 glass

Ferromagnetic oxide glass were obtained by rapid-quenching in the ternary system of (Fe 2 O 3 ) x -(CaO) y - (B 2 O 3 ) z . Specimens with x more than 0.65 were not glassy but crystalline. The maximum value of magnetization at room temperature, 19.5 eμ/g, was observed for x:y:z=0.55:0.15:0.3. The specimen heated once above the crystallization temperature lost its magnetization. The measurement of magnetic properties, Mossbauer spectra and DTA suggested this glass would be a new type amorphous magnetic material.

New intermetallic compounds found in Hf–Ni–Ge and Hf–Pt–Ge systems

Abstract New intermetallic compounds, Hf3Ni4Ge4 and HfPtGe, were found and their crystallographic, electric and magnetic properties were characterized. Hf3Ni4Ge4 has an orthorhombic structure (space group Immm) with lattice constants of a=1.2873 nm, b=0.6484 nm, and c=0.3892 nm and shows typical Curie-paramagnetic behavior between 2 K and 300 K and a metallic temperature dependence of the resistivity at temperatures between 10 and 250 K. HfPtGe has an orthorhombic structure (space group Pnma) with lattice constants of a=0.6603 nm, b=0.3950 nm, and c=0.7617 nm and shows diamagnetism and a metallic temperature dependence of the resistivity.

Tunneling studies on Ba1−xKxBiO3 single crystals with Tc = 15–30 K

Abstract Tunneling measurements have been performed on high-quality Ba 1− x K x BiO 3 single crystals with T c s between 15 and 30 K. The junctions are Ba 1− x K x BiO 3 /natural barrier/Au sandwich type, which exhibit very low leakage currents at zero bias and sharp conductance peaks at the gap-edges. The average ratio of 2Δ/ k B T c = 3.5±0.1 is obtained using more than 20 different junctions (different samples) with T C s determined from tunnel junctions. Temperature dependence of the energy gap is consistent with the BCS prediction. Second derivative measurements of current-voltage characteristics have also been carried out. Observed strengths and peak positions of the superconducting phonon structures in d 2 I /d V 2 strongly support phonon-mediated superconductivity in Ba 1− x K x BiO 3 .

Magnetism and transport properties of Nd6Fe13−xAl1+x crystals

Abstract Nd 6 Fe 13− x Al 1+ x ( x =2.2 and 3.5) crystals were grown by the self-flux method, and their crystallographic, magnetic and electric properties were investigated. Nd 6 Fe 13− x Al 1+ x , which crystallizes in a tetragonal structure of space-group I4/mcm, shows peculiar successive magnetic transitions. In particular, Nd 6 Fe 9.5 Al 4.5 shows transitions at 20 K, 56 K and 128 K, and the spontaneous magnetization M s at 5 K (87.5 emu/g) can be explained by assuming ferromagnetic Fe sublattices (4d↑16k↑16l 1 ↑16l 2 ↑) and ferrimagnetic Nd sublattices (8f↓16l↑). Nd 6 Fe 9.5 Al 4.5 seems to adopt ferrimagnetism in which the spontaneous magnetization is parallel to the 〈100〉 directions at temperatures below 20 K. A small ferromagnetic moment component, which is induced by canting of the antiferromagnetically coupled spins along the [001] direction, exists in the [100] direction at temperatures of 20 K T T T

New Intermetallic Compound Found in Sm–Fe System

A new intermetallic compound, SmFe7, has been found in the Sm–Fe system. We grew SmFe7 single crystals via a self-flux method. Precise X-ray analysis revealed that SmFe7 has a tetragonal structure with a space group of P42/mnm and lattice constants of a=0.8765 and c=1.2133 nm. The structure is very similar to that of R2Fe14B (R=rare earth) except that the boron sites of R2Fe14B are vacant. Magnetization measurement results suggest that SmFe7 is a ferrimagnet with a significantly large spontaneous magnetization (136 emu/g at 293 K) and a huge anisotropy constant (K1+K2~-6.9×107 erg/cc at 293 K).