T. Eto

High-pressure apparatus for the measurement of thermal and transport properties at multi-extreme conditions

A high-pressure apparatus which we can use at low temperature and high magnetic field has been designed for making measurements of thermal and transport properties of condensed matter. The details of the apparatus and some examples of the measurements are described and briefly discussed. It is proved that the apparatus is suitable for use up to hydrostatic pressure of ~ 3.5 GPa, down to ~ 2.0 K and up to ~ 11 T.

Effect of pressure on the superconductivity of RuSm1.4Ce0.6Sr2Cu2O10

Abstract A new hybrid ruthenate–cuprate superconductor RuSm1.4Ce0.6Sr2Cu2O10 was synthesized. This compound also exhibits magnetic ordering around 130 K . Electrical resistance measurement under high pressure has been carried out in order to clarify the interplay between magnetism and superconductivity. It is found that Tc increases but the magnetic ordering temperature decreases with pressure, i.e., the superconductivity competes with magnetic ordering.

Non-Fermi-liquid behaviour around the magnetic quantum critical point in UGa3

We studied the electronic state of UGa3 by measuring the electrical resistivity under pressure. When pressure is applied to UGa3, the Neel temperature TN = 67 K decreases steeply and becomes zero around 2.6 GPa. Correspondingly, the coefficient A in the electrical resistivity ρ = ρ0 + AT2, which is characteristic for Fermi liquid, increases steeply with increasing pressure. Around a magnetic quantum critical point of 2.6 GPa, a non-Fermi-liquid behaviour is found, showing a linear T-dependence of the resistivity, although the Fermi-liquid behaviour recovers above 4 GPa and the A-value decreases with increasing pressure. Furthermore, a resistivity drop, which might be related to superconductivity, was found below 0.3 K at 1.5 GPa, where the residual resistivity ρ0 has a maximum.

Pressure effect on antiferromagnetic ordering in UIn3

Pressure phase diagram of the antiferromagnet UIn 3 was constructed from the electrical resistivity measurement under high pressures up to 9 GPa. A Neel temperature increases monotonically with inc...

Anisotropy of Linear Thermal Expansion and Compressibility of Y 2 Fe 17 Under Pressure and its Correlation to Magnetic Structure

A complex temperature dependence of a.c. susceptibility of Y 2 Fe 17 under high pressures together with recent neutron diffraction studies under pressure proved the instability of the collinear ferromagnetic structure and the development of a non-collinear magnetic arrangement of Fe moments in Y 2 Fe 17 . To study the correlation between magnetic structure and volume in more detail we performed compressibility and linear thermal expansion studies under high pressures up to 100 kbar and 10 kbar, respectively. The compressibility in the paramagnetic state s P (above 10 kbar at room temperature) was determined from the Murnaghan equation of state using the X-ray data, \kappa_{P}=0.80\ {\rm Mbar}^{-1} . The linear thermal expansion and compressibility in the ferromagnetic state at low temperatures are highly anisotropic. As a consequence, the c/a ratio decreases with increasing pressure. The magnetic phase diagram of Y 2 Fe 17 compound was compiled up to 20 kbar.

The effect of pressure on the superconductivity and magnetism of RuSr2GdCu2O8

A new hybrid ruthenate-cuprate superconductor RuSr 2 GdCu 2 O 5 has been synthesized. This compound exhibits superconductivity and magnetic ordering around 40 K (=T c ) and 130 K (=T m ). The effect of pressure on the electrical resistance has been measured up to 2.1 GPa in order to make clear the interplay between the magnetism and the superconductivity. It is found that both T c and T m increase with pressure with rates of dT c /dP = 1.9 K GPa -1 and dT m /dP = 5.7 K GPa -1 , which indicates that the superconductivity does not compete with the magnetic ordering. An x-ray diffraction experiment under pressures up to 13 GPa has been carried out in order to clarify the relation between the electronic properties and the lattice compression.

Collapse of 5 f -Electron Ferromagnetism in UPtAl Under High Pressures

UPtAl exhibits a ferromagnetic ordering of U magnetic moments at temperatures below T C =42.5 K. The magnetic-ordering transition is accompanied by an anomaly in the temperature dependence of electrical resistivity. This allows us to determine the value of Curie temperature from 𝜌 vs. T data that can be measured at very high pressures, at which reliable magnetization measurements are difficult. We report on resistivity measurements performed on an UPtAl single crystal under hydrostatic pressures p h 8 GPa. It was observed that the initial increase of T C with p becomes gradually reduced for p >2 GPa until the maximum T C value of , 48 K is reached between 4 and 6 GPa that is followed by a progressively developing downturn of the T C ( p ) curve. The latter result is attributed to the approaching collapse of the U 5 f -moment ferromagnetism. Low-temperature resistivity data point to a rapidly reduced magnetic anisotropy at highest pressures.

Magnetism in UPtAl under high pressure

UPtAl exhibits ferromagnetic ordering (TC = 42.5 K) of uranium 5f-electron moments. The magnetic ordering transition is accompanied by an electrical-resistivity (ρ) anomaly at Curie temperature (TC). We report on resistivity measurements performed in a wide temperature range on a UPtAl single crystal under hydrostatic pressures p ≤ 8 GPa. The initial increase of TC with p becomes gradually reduced for p > 2 GPa. The maximum TC value is reached between 4 and 6 GPa that is followed by a decrease of TC beyond 6 GPa. The latter result is attributed to the approaching collapse of U 5f moment ferromagnetism.

Forced Magnetostrictions and Magnetizations of Ni2+xMnGa1−x at Its Curie Temperature

Experimental investigations into the field dependence of magnetization and the relationship between magnetization and magnetostriction in Ni2+xMnGa1−x (x = 0.00, 0.02, 0.04) alloy ferromagnets were performed following the self-consistent renormalization (SCR) spin fluctuation theory of itinerant ferromagnetism. In this study, we investigated the magnetization of and magnetostriction on Ni2+xMnGa1−x (x = 0.02, 0.04) to check whether these relations held when the ratio of Ni to Ga and, the valence electron concentration per atom, e/a were varied. When the ratio of Ni to Ga was varied, e/a increased with increasing x. The magnetization results for x = 0.02 (e/a = 7.535) and 0.04 (e/a = 7.570) suggest that the critical index δ of H ∝ Mδ is around 5.0 at the Curie temperature TC, which is the critical temperature of the ferromagnetic–paramagnetic transition. This result confirms Takahashi’s spin fluctuation theory and the experimental results of Ni2MnGa. The spontaneous magnetization pS slightly decreased with increasing x. For x = 0.00, the spin fluctuation parameter in k-space (momentum space; TA) and that in energy space (T0) were obtained. The relationship between peff/pS and TC/T0 can also be explained by Takahashi’s theory, where peff indicates the effective magnetic moments. We created a generalized Rhodes-Wohlfarth plot of peff/pS versus TC/T0 for other ferromagnets. The plot indicates that the relationship between peff/pS and T0/TC follows Takahashi’s theory. We also measured the magnetostriction for Ni2+xMnGa1−x (x = 0.02, 0.04). As a result, at TC, the plot of the magnetostriction (ΔL/L) versus M4 shows proportionality and crosses the origin. These magnetization and magnetostriction results were analyzed in terms of Takahashi’s SCR spin fluctuation theory. We investigated the magnetostriction at the premartensite phase, which is the precursor state to the martensitic transition. In Ni2MnGa system alloys, the maximum value of magnetostriction is almost proportional to the e/a.