Wei Zhang

High-Magnetic-Field X-ray Absorption Spectroscopy of Field-Induced Valence Transition in YbInCu4

The magnetic field-induced valence transition in YbInCu 4 has been studied by X-ray absorption spectroscopy at the Yb L III -edge up to 41 T. The field-induced valence transition is clearly observe...

High Field X-ray Diffraction Study on a Magnetic-Field-Induced Valence Transition in YbInCu4

We report the first high-field x-ray diffraction experiment using synchrotron x-rays and pulsed magnetic fields exceeding 30 T. The lattice deformation due to a magnetic-field-induced valence transition in YbInCu 4 is studied. It has been found that the Bragg reflection profile at 32 K changes significantly at around 27 T due to the structural transition. In the vicinity of the transition field, the low field and high field phases alternate with the discontinuous change in the lattice constant. Thus, it is evident that the field-induced valence state transition is a first-order phase transition. The field dependence of the low-field-phase Bragg peak intensity is found to be roughly scaled with the magnetization.

Effect of substitution of Mn with Fe or Cr in Heusler alloy of Co2MnSn

Crystallographic and magnetic properties of Co2Mn1−xFexSn and Co2Mn1−y CrySn Heusler alloys were studied using x-ray diffraction, scanning electron microscopy with energy dispersive x-ray analysis, magnetization measurements and Mossbauer spectroscopy. We found that the intermetallic compounds crystallize into a single phase with the L 21-type Heusler structure at the concentration of 0≤x≤0.5 for Co2Mn1−xFexSn and 0≤y≤0.3 for Co2Mn1−yCrySn. The spontaneous magnetization increases when Mn is substituted with Fe and decreases when Mn is substituted with Cr. The values of hyperfine field at the Sn nuclear sites in Co2Mn1−xFexSn and Co2Mn1−yCrySn also increase or decrease in combination with the size of magnetization. These measurements suggest that the Slater–Pauling behaviour in half-metallic full-Heusler alloys provides a good description of the substitution effect of Mn with Fe or Cr.

Volume effect on the valence transition in Yb1−xRxInCu4 (R=Y, La, Ce, Lu) compounds

Abstract The effect of alloying on the first-order valence transition in Yb 1− x R x InCu 4 (R=Y, La, Ce, Lu) has been studied by magnetization measurements. It has been found that the transition temperature T v increases by substitution of La and Ce for Yb and decreases for the Y and Lu substitutions. In order to reveal the volume contribution to the change of T v , we measured lattice parameters of Yb 1− x R x InCu 4 at room temperature. The lattice parameter increases with x for R=Ce, La, Y and slightly decreases for R=Lu. Using the data of compressibility and the pressure effect on T v for YbInCu 4 we found that the changes of T v by La and Ce alloying are consistent with the volume change. However, both Y and Lu substitutions for Yb lead to a decrease in T v , inconsistent with the volume change. Possible reasons for the decrease of the Kondo temperature below T v by Y and Lu alloying are discussed.

Magnetic anisotropy of pure and doped YbInCu4 compounds at ambient and high pressures

The susceptibility and high-field magnetization of single-crystalline Yb1−xYxInCu4 (x = 0, 0.2 and 0.3) samples have been measured for different field orientations at ambient and high pressures. The compounds with x = 0 and 0.2 undergo a first-order valence transition from the intermediate-valence state to the trivalent state on increasing either temperature or magnetic field. The magnetization and susceptibility of these compounds have appreciable anisotropy in both states. The magnetic phase diagram of Yb1−xYxInCu4 determined at ambient pressure is also anisotropic, which is explained by the crystal-field calculations for the free Yb ion in the high-temperature phase. Moreover, the low-temperature magnetization process for x = 0.2 and 0.3 has been measured in low fields under high pressure; it shows anisotropic ferromagnetic ordering.

Alloying and pressure effect on the mixed-valence state of Yb in YbInCu4

The susceptibility and thermal expansion of Yb1?xRxInCu4 (; R = ?Y, La and Ce) have been measured at ambient and high pressures. These compounds undergo a first-order valence transition from an intermediate-valence state to a nearly trivalent state with increasing temperature. The valence change at the transition is for YbInCu4. It decreases on both alloying and applying pressure for all the compositions studied. From the pressure effect on the susceptibility of YbInCu4, the Gr?neisen parameter for the Kondo energy ?K is determined to be ?34.5 and ?20 for the low-temperature and the high-temperature state, respectively. The ? coefficient characterizing the hybridization strength between the 4f and conduction electrons for the intermediate-valence state is nearly five times larger than that for the high-temperature local-moment state. The obtained results suggest that the change of the 4f?conduction band electron hybridization rather than the volume dependence of the Kondo interaction is responsible for a large modification of the physical properties of the YbInCu4-based compounds at the valence transition.

High field NMR study of Yb0.9Y0.1InCu4 up to 30 T

NMR measurements of 115 In in Yb 0.9 Y 0.1 InCu 4 were performed at 4.2 K up to 30 T with a hybrid magnet installed in National Institute for Materials Science (NIMS). Fourier-transformed (FT) spectrum at a constant magnetic field was obtained by summing a set of FT spectra with shifting the transient frequency. A first-order valence transition was observed at 22 T. Coexistence of the valence-fluctuating phase and the field-induced phase was confirmed. It was found that the proportion of the field-induced phase continues to increase even at 30 T. The effect of 4 f -electron spin correlations in the field-induced phase on the spin–spin relaxation time T 2 was discussed.

Effect of pressure on first-order valence transition of Yb1−xYxInCu4

Abstract YbInCu4 exhibits a first-order valence transition at H v ≈33 T with 0.45% decrease of volume as increasing the magnetic field. The inherent chemical pressure in Yb1−xYxInCu4 system is discussed as negative on valence transition of YbInCu4. The external pressure effect on Hv of Yb1−xYxInCu4 is measured as d H v / d P≈−1 T kbar −1 .