F. Honda

Long-period, longitudinal spin density modulation in an itinerant 5f magnetic compound UCu2Si2

The magnetic structure of UCu2Si2 has been studied by means of neutron scattering. We have observed the first- and very weak third-order incommensurate satellite reflections for 100 K<T<106 K with the propagation q = [0 0 δ], δ = 0.116 at T = 101 K, indicating nearly sinusoidal magnetic modulation with long periodicity of Λ = 85.7 A. The intensity of the first-order satellite reflections is consistent with a moment direction parallel to the c-axis. The second-order satellite due to lattice modulation accompanied by a charge density wave could not be detected within our experimental sensitivity. The long-period magnetic modulation in UCu2Si2 cannot be explained in terms of an ANNNI model based on frustrated antiferromagnetic short-range interactions. The nearly sinusoidal long-period modulation is evidence for a spin density wave state as a consequence of itinerant behaviour of the 5f electrons in UCu2Si2. The ferromagnetic ground state and the very weak upper critical field for the incommensurate phase are consistent with the long periodicity.

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.

High-pressure studies of Kondo-like perovskite (La0.1Ce0.4Sr0.5)MnO3

Abstract The influence of hydrostatic pressure on electrical resistance of a perovskite manganese oxide (La 0.1 Ce 0.4 Sr 0.5 )MnO 3 has been investigated under pressures up to 1.8xa0GPa in the temperature range of 77–320xa0K. With application of pressure, Curie temperature ( T C ) increases at a rate of d T C /d p =+1.9 K/GPa . It is also found that the coefficient of −log T term originated from Kondo-like effect decreases with increasing pressure and the resistance maximum temperature ( T max ) shifts largely to lower temperature at a rate of d T max /d p =−86 K/GPa .

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.

Magnetoelasticity of UPtAl

Abstract Ferromagnetic ordering in UPtAl ( T C =42.5 K, M s =1.4 μ B ) is accompanied by a spontaneous magnetostriction reaching at low temperatures −3×10 −4 and 2×10 −4 in the basal plane ( λ a ) and along the c -axis ( λ c ), respectively. The volume effect ω s =2 λ a + λ c is −4×10 −4 . Application of external pressure yields reduction of the spontaneous moment at a rate d M s /d p =−0.027 μ B /GPa, while the Curie temperature increases, d T C /d p =2.5 K/GPa.

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.

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.

Magnetic phase diagram of UNi2Si2 under pressure

Abstract The influence of combined application of external hydrostatic pressure and a magnetic field parallel to the c-axis on the magnetic phases in UNi2Si2 was studied by measuring electrical-resistivity anomalies related to magnetic phase transitions. As a result, the pressure evolution of the B–T magnetic phase diagram is presented. Both the magnetic field and the pressure promote the ground-state uncompensated antiferromagnetic phase at the expense of the AF-I phase, which exists at higher temperatures. The value of the critical field for suppression of the AF-I phase becomes considerably reduced with increasing pressure. The applicability of the mean-field approach within the axial Ising model for explaining pressure effects on magnetic phase transitions is discussed.

Electrical Resistivity of Ce2Ir3Ge5 under High Pressure

We measured electrical resistivity on antiferromagnet Ce 2 Ir 3 Ge 5 under high pressure up to 8 GPa. It is shown that the Neel temperature (=9.5 K) at ambient pressure decreased by increased pressure. The Neel temperature seems to be zero at a critical pressure P c ≃2.0 GPa suddenly. The variation by higher pressure above 2.0 GPa does not seem prominence up to 8 GPa.