Tetsuya Fujiwara

Pressure-induced Magnetic Transition in a Single Crystal of YbCo2Zn20

We have measured the electrical resistivity of a single crystal of YbCo 2 Zn 20 at pressures up to 2.37 GPa and at temperatures from 50 mK to 300 K. Above a critical pressure P c (∼1 GPa), we have found a resistivity anomaly at T M (∼0.15 K at 1 GPa) that increases with the pressure. At the ambient pressure, the system shows a nonmagnetic ground state described by the Fermi-liquid model. The T 2 coefficient of the electrical resistivity A strongly increases with the pressure upon approaching P c . However, in the vicinity of P c , the temperature dependence of the resistivity deviates from the Fermi-liquid description. These observations suggest that the application of hydrostatic pressure induces a magnetically ordered state for P ≥ P c and T ≤ T M .

Switching of Magnetic Ordering in CeRhIn5 under Hydrostatic Pressure

Magnetic neutron diffraction measurements were carried out on the heavy-fermion antiferromagnet CeRhIn 5 under hydrostatic pressure. The incommensurate (IC) magnetic ordering is known to be charact...

Development of a low-temperature insert for precise magnetization measurement below t = 2k with a superconducting quantum interference device magnetometer

We have developed a 9-mm-diameter 3He insert for precise magnetization measurements below T = 2 K that is attachable to a commercial superconducting quantum interference device magnetometer. The insert is made from a thin-walled stainless steel pipe with an inner diameter of 6.2 mm, which determines the maximum sample size. 3He gas is condensed in the pipe, which is liquefied by 4He gas at T ~1.8 K generated by the magnetometer via the heat exchanger of a Cu vacuum jacket with an outer diameter of 8.6 mm soldered to the stainless steel pipe. The temperature of the insert is decreased to T ~0.5 K by evacuating liquid 3He using a rotary pump and then to T = 0.36 K with a sorption pump. From the diamagnetization signal of a superconducting Al chip with a mass below 0.1 mg, the magnetization resolution with the insert is confirmed to be less than 10-7 emu. To examine the performance of the insert, we measured the temperature dependence of the magnetic susceptibility and magnetization for Pr0.6La0.4Ag2In down to T = 0.4 K.

Component-separated magnetic transition in HoRh2Si2 single crystal

Magnetic susceptibility and specific heat measurements have been carried out on a HoRh2Si2 single crystal compound. Specific heat shows two λ-like anomalies at TN1=29.1 K and TN2=12.0 K, and an additional sharp anomaly indicating the first order transition at Tt=27.3 K. The temperature dependence of susceptibility along the [001] direction shows a clear cusp at TN1 but a tiny kink at TN2 and Tt. In contrast, those in the ab-plane show a clear cusp at TN2. HoRh2Si2 shows a successive component-separated magnetic transition coming from a new type frustration not geometrical one.

Pressure-Induced Commensurate Magnetic Order in Multiferroic HoMn2O5

H. Kimura, ∗ K. Nishihata, Y. Noda, N. Aso, K. Matsubayashi, Y. Uwatoko, and T. Fujiwara Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan Institute for Solid State Physics, The University of Tokyo, Tokai, Ibaraki 319-1106, Japan Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan Graduate School of Science and Engineering, Yamaguchi University, Yamaguchi 753-8512, Japan (Dated: April 23, 2008)The pressure–temperature ( p – T ) phase diagram for microscopic magnetism in the multiferroic compound HoMn 2 O 5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate–commensurate–incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The p – T phase diagram established shows excellent agreement with the recently reported p – T dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the p – T magnetic phase diagram is quite similar to the previously obtained magnetic field–temperature phase diagram.The pressure–temperature ( p – T ) phase diagram for microscopic magnetism in the multiferroic compound HoMn 2 O 5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate–commensurate–incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The p – T phase diagram established shows excellent agreement with the recently reported p – T dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the p – T magnetic phase diagram is quite similar to the previously obtained magnetic field–temperature phase diagram.

Nonlinear susceptibility measurement for quadrupolar response in a dilute Γ3 Non-Kramers Doublet System Pr0.05La 0.95Pb3

We measure the temperature dependence of the nonlinear susceptibility χ3, which reflects the fluctuation of quadrupolar moments, in Pr0.05La0.95Pb3 with a Γ3 non-Kramers doublet in the crystal-electric-field ground state to provide evidence of the quadrupolar Kondo effect. Non-Fermi liquid behavior of χ3 with a \(-\ln T\) dependence is detected in the [100] and [110] directions below \(T\approx 2.5\) K, suggesting the screening of quadrupolar moments. In contrast, χ3 in the [111] direction becomes constant below \(T\approx 3\) K. The observed features indicate that a low-lying Γ3 doublet plays a crucial role in the anomalous properties of PrxLa1-xPb3.

Magnetization processes and phase diagram of HoRh2Si2 single crystal having a component-separated magnetic transition

Thermal variations of magnetization under various magnetic fields and magnetization processes at various temperatures have been studied on a HoRh2Si2 single crystal compound. Three anomalies at TN1=29.1 K, Tt=27.3 K and TN2=12.0 K exist at low field in the thermal variation. The thermal dependence of M/B and the magnetization change drastically with magnetic field. Step-like metamagnetic processes appear along the all directions below TN2; two-step ones appear along the [001] and [100] directions, and a one-step one appears along the [110] direction. For TN2<T<Tt, a two-step metamagnetic one persists along the [001] direction whereas the processes along directions in the basal plane become a paramagnetic like one. The B001-T magnetic phase diagram is constructed, in which there are at least five ordered phases. Two field-induced magnetic phases appear for low and high temperatures.

Novel magnetic behaviour of GdPd2Si2 single crystal

Magnetic and specific heat measurements have been performed on a GdPd2Si2 single crystal compound having the tetragonal ThCr2Si2-type crystal structure. Specific heart shows two λ-type anomalies at TN=16.7 K, T1=12.3 K and a small hump with hysteresis at T2=6.8 K; there are three phases below TN. The magnetic entropy of Rln6 is released below TN. The temperature dependence of magnetic susceptibility shows a very peculiar behaviour. With decreasing temperature, the magnetic susceptibility along the [001] direction increases through a small kink at TN down to T1 where a clear cusp is seen, decreases rapidly below TN, then shows an upturn and a clear kink at T2 followed by a gradual increase. This behaviour examines at various magnetic field along [001] and [100]. The B001-T and B100-T magnetic phase diagrams have been constructed. The field-induced phase appears near by the 100] magnetic field, B100.

Electrical transport properties of ternary phosphides RRu2P2 (R=La, Ce,Pr and Eu) with ThCr2Si2 type crystal structure

It was found the growth method of single crystals of ternary lanthanide transition metal phosphide RRu2P2 (R=La, Ce,Pr and Eu) with enough large volume to measure the macroscopic physical properties, such as magnetization, electrical resistivity and specific heat. As a result, we succeeded in the measurements of electrical resistivity with a sufficiently good accuracy and reveal an experimental evidence of the superconducting transition in LaRu2P2 for the first time. On the basis of the results of electrical resistivity measurements we discuss that how P-P bonding state does affect on the electrical transport properties of RRu2P2 compounds.

Magnetoresistivity of YbCo2Zn20 at low temperature

We have studied the electrical resistivity of YbCo2Zn20 under magnetic field up to 18 T. With applying magnetic field, the contribution of the Kondo interaction to the electrical resistivity is suppressed and the Fermi liquid regime is extended to higher temperature range. Both the T2 coefficient of the electrical resistivity A and the residual resistivity ρ0 strongly decrease in magnetic field. From the magnetic variation of the resistivity, it has been found that YbCo2Zn20 is classified as a heavy fermion system with small Kondo temperature of ~ 1.0K.