Hiroaki Samata

Magnetic anisotropy and magnetostriction of SmFe2 crystal

Abstract Magnetic anisotropy and magnetostriction of SmFe 2 crystal were studied. Crystals were grown by a self-flux method using Sm as a flux. Magnetic anisotropy and magnetostriction were measured by means of a torque magnetometer and a new optical technique, respectively. SmFe 2 shows a typical cubic anisotropy with anisotropy constants K 1 =−5.3×10 6 and K 2 =1.9×10 6 xa0erg/cm 3 at 300xa0K. Though the easy axis of magnetization is parallel to the [1xa01xa00] direction at low temperatures, it changes to the [1xa01xa01] direction at temperatures above 195xa0K. Magnetostriction constants were determined to be λ 111 =−2010×10 −6 , λ 100 =−130×10 −6 and λ s =−1258×10 −6 at 300xa0K. The magnetoelastic contribution ΔK 1 (∼−8.8×10 6 erg/cm 3 ) to the anisotropy constant seems to be larger than the intrinsic anisotropy constant K 1int (∼3.5×10 6 xa0erg/cm 3 ) in SmFe 2 . If this is the case, easy axis of magnetization has been changed from the 〈1xa00xa00〉 direction ( K 1int >0) to the 〈1xa01xa01〉 direction (effective anisotropy K 1eff = K 1int +Δ K 1

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.

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.

Magnetism and transport properties of metamagnetic Mn1-xCrxAu2

Abstract Crystallographic, magnetic and electric properties of metamagnetic Mn1−xCrxAu2 were studied. Pure MnAu2 has a helical-spin structure and the structure changes to a ferromagnetic state below the Neel temperature TN (∼360 K) and above a threshold magnetic field Hth (∼10 kOe at 300 K). The TN, Hth for the metamagnetic transition, and the helical angle of the helical-spin configuration decreases as the Cr content x increases. The Cr substitution seems to dilute the magnetism of MnAu2 and to weaken the interlayer magnetic coupling between the Mn spins. A significant magnetoresistance as large as 3.5% was observed at room temperature in magnetic fields below 10 kOe. The metamagnetic transition seems to give rise to the magnetoresistance via s–d scattering.

CRYSTAL GROWTH AND PROPERTIES OF NEW RUTHENIUM OXIDES

Abstract New ruthenium oxide crystals of NaBa 3 Ru 2 O 10 , (Na 0.57 Sm 0.43 )Ba 3 Ru 2 O 10 and (Na 0.74 Dy 0.26 )Ba 3 Ru 2 O 10 were synthesized by an electrochemical method using molten NaOH as an electrolyte, and their crystallographic, electric and magnetic properties were characterized. All the crystals have hexagonal structure of space group P6 3 mc and exhibit semiconductive behavior with activation energies of 0.19, 0.19 and 0.38xa0eV, respectively, for NaBa 3 Ru 2 O 10 , (Na 0.57 Sm 0.43 )Ba 3 Ru 2 O 10 and (Na 0.74 Dy 0.26 )Ba 3 Ru 2 O 10 crystals. In addition, all the crystals have negative asymptotic Curie temperatures. They appear to have antiferromagnetic orders; however, antiferromagnetic transition was not observed in the magnetization measurement down to 2xa0K. Effective magnetic moment P eff was determined to be 0.49, 0.85 and 2.07xa0 μ B /f.u. for NaBa 3 Ru 2 O 10 , (Na 0.57 Sm 0.43 )Ba 3 Ru 2 O 10 and (Na 0.74 Dy 0.26 )Ba 3 Ru 2 O 10 .

Magnetic and superconducting properties in the Y1−xDyxNi2B2 system

Abstract We measured the magnetic and superconducting properties in intermetallic compounds Y 1−x Dy x Ni 2 B 2 C(0 ≤ x ≤ 1.0) over wide temperature and magnetic field ranges. The reduction of the superconducting temperature is mainly caused by the magnetic pair breaking effect due to the existence of Dy +3 paramagnetic ions. The long-range magnetic ordering for samples with high Dy composition is through the Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The exchange interaction is strongly modulated by the Dy +3 -moment separation. The small value of the Curie-Weiss temperature suggests that the coupling between the conduction electrons and the magnetic moment is not too strong. There is no evidence to show the co-existence of long-range magnetic ordering and superconductivity in the Y 1−x Dy x Ni 2 B 2 C system. The small value of k for the Dy-doped YNi 2 B 2 C compound indicates that the Yue5f8Niue5f8Bue5f8C compound is not a strongly type-II superconductor.

Electrochemical crystal growth of superconducting cuprates

Abstract An electrochemical method was applied to grow crystals of La 2 CuO 4 and Nd 2 CuO 4 at temperatures below 400 °C in a zirconium bath using molten NaOH as an electrolyte. The La 2 CuO 4 crystal grown at 320 °C shows superconductivity with the onset transition temperature of 25 K without any heat treatment in oxygen. The results of EPMA, AES and iodometory revealed that the crystal is oxygen rich La 2 CuO 4 + δ without any substitution of La by Na. The crystals seem to be highly oxidized in the process of the electrochemical deposition. In the case of Nd 2 CuO 4 , crystals were grown at 380 °C. However, the substitution of Nd by a large amount of Ce was unsuccessful.

CRYSTAL GROWTH AND SUPERCONDUCTIVITY OF (Sm0.75Ce0.25)2Sr2Cu2NbO10−δ

Abstract Single crystals of (Sm 0.75 Ce 0.25 ) 2 Sr 2 Cu 2 NbO 10−δ (SCSCNO) were grown by a flux method using SrCu 6 O y as flux, and their morphology and superconductivity were investigated. We found that the as-grown crystal consists of SCSCNO and SmSr 2 Cu 2 NbO 8 (SSCNO) crystal layers, with the SCSCNO layer being sandwiched between two non-superconducting SSCNO crystal layers. The SSCNO layers can be removed by chemical etching with HCl solution. The SCSCNO crystal shows a superconducting transition at about 17xa0K, and the superconducting volume fraction increased when the crystals were annealed in an oxygen atmosphere.

A new electrolysis-cell method for the synthesis of oxide crystal

Abstract A new ‘Electrolysis-Cell Crystal Growth’ technique for the synthesis of oxide single crystals is introduced. In this method electrolyte of molten KOH solution and metal electrodes form an electrolysis cell, and crystal growth is performed using the electromotive force of the cell itself without using any external electric power-supply. As an example, the method was applied to the crystal growth of Ba 1−x K x BiO 3 , and the characterization of the crystal has been performed.