Hideto Fukazawa

From Mott insulator to ferromagnetic metal: A pressure study of Ca2RuO4

We show that the pressure-temperature phase diagram of the Mott insulator Ca2RuO4 features a metal-insulator transition at 0.5 GPa: at 300 K from paramagnetic insulator to paramagnetic quasi-two-dimensional metal, and at Tless than or equal to12 K from antiferromagnetic insulator to ferromagnetic, highly anisotropic, three-dimensional metal. We compare the metallic state to that of the structurally related p-wave superconductor Sr2RuO4, and discuss the importance of structural distortions, which are expected to couple strongly to pressure.

Filling Control of the Pyrochlore Oxide Y2Ir2O7

We report the filling control of the pyrochlore oxide Y2Ir2O7. Metallic ground state appears with increasing substitution content x (x >= 0.3). We have revealed that the density of states at the Fermi level rapidly changes with x by this filling control of Y2Ir2O7.

Anisotropic release of the residual zero-point entropy in the spin ice compound Dy2Ti2O7: Kagome ice behavior

We report the specific heat and entropy of single crystals of the spin ice compound

A Kagome ice state in the spin ice compound Dy2Ti2O7

{mathrm{Dy}}_{2}{mathrm{Ti}}_{2}{mathrm{O}}_{7}

Filling control of the Mott insulator Ca2RuO4

at temperatures down to 0.35 K. We apply magnetic fields along the four characteristic directions [100], [110], [111], and [112]. Because of Ising anisotropy, we observe anisotropic release of the residual zero-point entropy, attributable to the difference in frustration dimensionality. In the high magnetic field along these four directions, the residual entropy is almost fully released and the activation entropy reaches

Intrinsic properties of the Mott insulator Ca2RuO4+δ (δ=0) studied with single crystals

Rmathrm{ln}2.

Low Temperature Specific Heat of Dy2Ti2O7 in the Kagome Ice State

However, in the intermediate-field region, the entropy in the fields along the [111] direction is different from those for the other three field directions. For the [111] direction, the frustration structure changes from that of the three-dimensional pyrochlore to that of a two-dimensional Kagome-like lattice with constraint due to the ice rule, leading to different values of the zero-point entropy.

Pressure-induced ferromagnetic metal for a Mott insulator Ca2RuO4

We report on the specific heat and the entropy of single crystals of the spin ice compound Dy2Ti2O7 down to 100 mK under magnetic fields along the [111] direction in order to study detailed low temperature properties of the Kagome ice state. Previously, we reported anisotropic release of the residual entropy reflecting the Ising anisotropy. We pointed out that the anisotropic behaviour can be viewed as the difference in frustration dimensionality. In an intermediate field, the entropy for the [111] field direction is different from those of the other principal directions. This is because the frustration structure changes from that of a three-dimensional (3D) pyrochlore to that of a two-dimensional (2D) Kagome lattice with constraint from the ice rule, accompanied by a different zero-point entropy value. We call this state the Kagome ice state. In the Kagome ice state, the value of the residual entropy, ΔSKagome, is estimated as 0.598 J K−1/(mol Dy) by Paulings method. In the present experiment, we observed that the specific heat at 1 T exhibits a sharp peak at 400 mK and an anomalous upturn at lower temperature. This peak indicates the entropy release from a 1-in 3-out state with no residual entropy to a 1-in 3-free state.

Raman scattering studies of Ca 2 - x Sr x RuO 4

We have grown single crystals of electron doping system Ca 2- x La x RuO 4 (0.00 ≤ x ≤0.20) by a floating zone method. The first order metal/non-metal transition and canted antiferromagnetic ordering occur for 0.00 < x < 0.15, similar to those in the bandwidth controlled system Ca 2- x Sr x RuO 4 (CSRO). However, comparing with CSRO, we found a rather different metallic ground state adjacent to the non-metallic ground state with canted antiferromagnetic order. Instead of short-range antiferromagnetic correlation found in CSRO (0.20 ≤ x < 0.50), the metallic ground state of the present system is characterized by strong ferromagnetic correlation.

Electronic structural change of (Sr,Ca)_2RuO4 studied by x-ray absorption spectroscopy

Abstract We will describe the growth of single crystals of the layered perovskite Ca 2 RuO 4 by a floating-zone method. We have confirmed that stoichiometric Ca 2 RuO 4 is a Mott insulator. Canted antiferromagnetic (CAF) ordering occurs below 113xa0K. We also discuss the development of a short-range CAF order below 150xa0K.