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We studied the dependence of the electronic specific heat Cel/T on the magnetic field up to H = 8 T in a dilute quadrupolar compound Pr0.05La0.95Pb3 with a non-Kramers Γ3 doublet in the crystal-ele...

The tetragonal ternary compound TbIr 2 Si 2 shows polymorphism; the ThCr 2 Si 2 -type structure as a low temperature phase (I-phase) and the CaBe 2 Ge 2 -type one as a high temperature phase (P-phase) exist. In order to compare with magnetism of the morphs, magnetic measurements were performed on the I- and P-phase single crystals. The magnetic behavior changes drastically depending on the structure. The TbIr 2 Si 2 (I) shows an antiferromagnetic ordering below T N =80 K, a strong uniaxial magnetic anisotropy with the easy [001] direction, and isotropic magnetic behavior in the basal plane. The [001] magnetization shows a clear two-step metamagnetic transition: an Ising-like behavior at low temperatures. On the other hand, the TbIr 2 Si 2 (P) has the comparatively low ordering temperature of T N1 =11.5 K and an additional transition temperature of T N2 =5 K, and exhibits an easy-plane magnetic anisotropy with the easy [100] direction. A strong magnetic anisotropy appears for high magnetic fields between the directions in the basal plane. Multi-step metamagnetic processes appear. In the both phases, the χ - T behavior suggests the existence of component-separated magnetic transitions. The ab -component of magnetic moments orders at the higher transition temperature T N1 for the P-phase compound, which is contrast to the I-phase behavior; the c -component orders firstly at T N in the I-phase. The crystalline electric field analysis was made, and the CEF effects explain the different of magnetic anisotropy between the both phases.

Magnetic measurements on pseudoternary compounds Ho1-xGdxRh2Si2, which substitute Gd having no quadrupole for Ho, were performed. They exhibit a successive component-separated magnetic transition; the c- and ab-components of magnetic moments independently order at different temperatures TN1 and TN2, respectively. The partial ordered state, a frustration appears for TN1 >T > TN2: for the phase II in the magnetic phase diagrams. In the ordered phase, step-like metamagnetic processes appear for TN2 > T; two-step ones appear along the [001] and [100] directions, and a one-step one appears along the [110] direction. The B-T magnetic phase diagrams were constructed. There are six, four and three ordered phases in the B001-T, B100-T and B110-T phase diagram, respectively. Two diagrams of the basal plane directions, B100-T and B110-T, resemble each other. Some interesting or peculiar phase boundaries appear. The Gd composition x dependence of transition temperatures is determined. The transition temperatures TN1 and TN2 increase with increasing x. The x-dependency of TN1 is well scaled by the de Gennes factor: (g-1)2J(J+1) whereas the transition of TN2 is not scaled. Some magnetic features declare that quadrupole interactions play an important role in this compound system.

Magnetic studies were performed on PrPd2Si2 single crystals which crystallize in the tetragonal ThCr2Si2-type structure. The temperature dependence of the magnetic susceptibility indicates that the compound orders antiferromagnetically at temperatures below T N = 3.2 K. The transition was confirmed by specific heat measurements. Magnetization measurements at fields up to 18 T show that the easy magnetization direction is the [100] direction in the basal plane. In the magnetization process, five or four metamagnetic transitions appear; the process is a five (four)-step metamagnetic one. The [110] magnetization process is a three-step one. A strong magnetic anisotropy between the [100] and [110] directions is observed within the basal plane for high magnetic fields. Along the hard magnetization direction of the c-axis, a metamagnetic transition appears. The B [100] − T phase diagram was constructed. A magnetic anisotropy between the [100] and [001] directions is also strong. These behaviors are discussed based on an analysis of crystalline field effects.

Measurements of the magnetization and the specific heat were performed on a PrRh2 single crystal. A strong magnetic anisotropy with the easy magnetization direction of the c-axis is observed. Four anomalies appear in the temperature dependence of magnetic susceptibility along the c-axis; a cusp at TN=52 K, a high peak at T3=38 K, a shoulder at T2=33 K and a small peak at T1=4 K are observed, indicating magnetic transitions. The specific heat also shows four anomalies at the temperatures where the magnetic anomalies appear, confirming the occurrence of successive magnetic transitions. A clear two-step metamagnetic process appears along the easy magnetization direction of the c-axis at low temperatures. The magnetization in the first step is almost constant and is corresponds to (1/5) Ms (Ms: saturation magnetization), indicating that this field-induced phase has a long period and a stable magnetic structure. A metamagnetic process is hypothesized on the basis of the magnetic structure. The B001 − T phase diagram is constructed.

The magnetic measurements in detail, especially high field magnetic measurements up to 45 T, have been performed on a TbPd2Ge2 single crystal. The compound shows an antiferromagnetic ordering below T N =14 K. High field magnetization shows that the magnetic easy direction is the [110] direction in the basal plane. The easy magnetization is saturated above about 25 T at 1.3 K and reaches 9.0 μB/f.u. Multi-step metamagnetic processes appear within the basal plane; that is, three-step and five-step metamagnetic processes appear along the [110] and [100] directions, respectively. The [001] magnetization process is a one-step metamagnetic one. All transitions persist up to near T N . The B 100–T and B 110–T magnetic phase diagrams were constructed, where there are five and three ordered phases, respectively. The crystalline electric field effects were examined. On the basis of the effects, the magnetization behavior has been discussed.

The cavitation surge is a kind of instability phenomenon generated in a liquid rocket engine, and it is known that when the inlet pressure of the turbopump of the engine is decreased, the frequency of cavitation surge continuously varied. On the other hand, it was observed in a turbopump test conducted in JAXA that the frequency of cavitation surge discontinuously decreased when the inlet pressure was decreased. Aiming at explaining this curious phenomenon, we conducted the linear analysis using the frequency-domain method and found that this phenomenon was a kind of self-excited vibration coupling the cavitation characteristics with the acoustic resonance of the inlet pipeline. However, the linear analysis could not simulate the phenomenon that a frequency of standing wave changed to the other mode at a certain inlet pressure. Therefore, we conducted the nonlinear analysis using the one-dimensional time-domain method. As a result, it was found that when the inlet pressure was decreased, the damping effect became larger in the higher frequency oscillation because of nonlinear factors. Consequently, the oscillation of higher frequency was intensely weakened and the oscillation of lower one appeared instead.

The magnetic measurements have been performed for high fields up to 18 T and low temperatures down to 0.5 K on the single crystal compound ErCu2Si2. In the temperature dependence of magnetic susceptibility, two anomalies are seen at TN=1.51 K and Tt=0.97 K which is corresponding to an antiferromagnetic ordering temperature and may come from a change of magnetic structure. Low temperature magnetization shows a metamagnetic transition around 0.4 T along the easy magnetization direction of [001]. The magnetization is almost saturated above 3 T and reaches 8.8μB/f.u. at 18 T. A metamagnetic transition appears around 0.5 T in the basal plane magnetization processes as well. The anisotropy within the basal plane is fairly large for high fields. These behaviors have been explained from crystalline electric field effects and magnetic interaction in terms of molecular field.

High field magnetization up to 18 T and magnetic susceptibility measurements have been carried out on a PrRh2Si2 single crystal. The anomalously high Neel temperature of 70 K is confirmed. A strong uniaxial magnetic anisotropy with the easy c-axis is evidenced. A sharp metamagnetic transition appears at 16 T in the easy c-axis magnetization process while magnetization in the basal plane is very small and the curve is linear. The saturation moment obtained is 3.1μB. Crystalline electric field (CEF) effects have been analyzed to discuss the magnetic behaviors.

Effects of pressure on the physical properties are very important for understanding highly correlated electron systems, in which pressure-induced attractive phenomena such as superconductivity and magnetically ordered non-Fermi liquid have been observed. Up to now, many scientists have developed a lot of high pressure apparatus for each purpose. In this paper, we present the very small “palm cubic-anvil high-pressure apparatus” for precise electric transport measurements under high pressure up to 8 GPa. The most outstanding characteristic of this pressure cell is its compactness. This cell enables us to measure absolute values of electrical resistivity, magneto-resistance and Hall coefficient at various temperatures. The details of our palm cubic high-pressure apparatus are introduced, and some neutron experimental results at room temperature are discussed.

Photoluminescence properties of Eu-implanted AlGaN with whole Al content are investigated. Strong photoluminescence (PL) lines attributed to 5D0 - 7Fj transitions of Eu3+ are observed from Eu-doped AlGaN with whole Al content. The PL intensity becomes maximum around Al content of x = 0.2. From the results of time-resolved PL, the decay time of Eu3+-related PL decreases with increasing Al content. The intensity enhancement effect of Eu3+-rerated luminescence by AlGaN is mainly due to the improvement of energy transfer efficiency rather than the improvement of transition probability of Eu3+ by changing the crystal field. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Al composition on luminescence properties corresponding to Tb 3+ inner level transitions are investigated. When the Al composition is larger than 0.3, luminescence corresponding to 5 D 4 - 7 F J (J = 3, 4, 5, 6) transitions is observed at room temperature, while 5 D 3 - 7 F J transition such as 5 D 3 - 7 F 5 can be observed only at low temperature. As the Al composition increases, the luminescence intensity is increased super linearly at first, and then linearly increased. Thermal quenching of luminescence intensity is dramatically improved as increasing the Al composition. Major effect of AlGaN is well explained by reduction of energy-back-transfer process.

Recessed-gate GaN metal-oxide-semiconductor field-effect transistors with a double-insulator gate configuration demonstrate 10-MHz switching operation of which delay time is

Er ions are introduced into Al x Ga 1-x N (0 ≤ x ≤ 1) by ion implantation to investigate the effect of Al composition on the luminescence properties of 4f n inner-shell transitions of Er 3+ . Strong and sharp emission peaks attributed to the 4f-4f transition of Er 3+ are observed in ultra-violet and blue region (400-550 nm) from the samples with AlN molar fraction of x > 0.3. These photoemissions are assigned as 2 P 3/2 - 4 I 15/2 , 2 P 3/2 - 4 I 13/2 , 2 P 3/2 - 4 I 11/2 , and 2P 3/2 - 4 H 11/2 transitions, and the 408 nm emission, corresponding to 2 P 3/2 - 4 I 13/2 transition, is the strongest in the present work. As increasing the Al composition, the intensity of Er 3+ -related emissions is rapidly increased and the thermal quenching properties is also improved.

The magnetic characteristics of the single crystal compound TbCu 2 Ge 2 have been studied by magnetic susceptibility and magnetization measurements. The susceptibility shows two anomalies at T N =12.3 K and T t =9.3 K. The magnetic easy direction is the [1 1 0] direction in the basal plane. The magnetization along the easy direction in the basal plane shows a multi-step (at least four steps) metamagnetic process. No significant change of the process is observed at T t . A one-step metamagnetic transition appears around 17 T in the hard c -axis magnetization process. This transition persists above T N up to 25 K where the susceptibility shows a broad peak. The origin is unsolved yet.

High performance enhancement-mode m -plane AlGaN/GaN heterojunction field-effect transistors were reported in this letter. +3 V threshold voltages, 230 mA/mm of maximum drain-source current (Ids(max)), and 58 mS/mm of maximum transconductance (gm(max)) were obtained. High Ids(max) and gm(max) were due to the regrown n+-GaN contact layer. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The measurements of the electrical resistivity ρ and the thermopower S of single crystal EuCo2P2 have been performed at temperatures from 1.5 to 300 K under hydrostatic pressures up to 3 GPa and in magnetic fields up to 10 T. The temperature dependences of ρ and S show drastic changes at a critical pressure Pc, which indicates a large modification of the electronic structure around the Fermi level due to the valence transition from Eu to Eu. In the low-pressure phase with magnetic Eu and nonmagnetic Co, the magnetic field dependences of ρ and S show sudden decrease at B ≈ 7 T, implying a metamagnetic transition. On the other hand, no drastic change in ρ(B) and S(B) curves is observed in the high-pressure phase with nonmagnetic Eu and magnetic Co.

Magnetic characteristics of a DyPd2Si2 single crystal with the ThCr2Si2-type structure have been studied from measurements of magnetic susceptibility (T) and magnetization M(B). It was found that DyPd2Si2 orders antiferromagnetically below TN = 9.2 K with the basal-plane [100] axis being the easy magnetization direction at high magnetic fields. Upon increasing magnetic field, the [100] magnetization curve exhibits at least six metamagnetic transitions at 0.2, 1.8, 3.0, 3.7, 4.2 and 6.1 T before reaching the saturation magnetization Ms = 10 B. Five metamagnetic transitions were detected on decreasing fields. For the [110] magnetization process, three metamagnetic transitions were evidenced. In contrast, the M(B) curve along the [001] axis, which is the hard magnetization direction, displays no metamagnetic transition; it shows a monotonous increase with a concave curvature up to 18 T. Finally, we constructed a comprehensive B100-T magnetic phase diagram consisting of six magnetic ordered phases.

We have performed pressure-dependent electrical resistivity measurements of a single crystal Ce 2 Pd 3 Si 5 , which is an antiferromagnetic Kondo lattice compound, at pressures up to 9.5 GPa and at temperatures down to ∼ 0.4 K . As the pressure is increased, the Neel temperature T N deduced from the temperature dependence of resistivity decreases steeply above 4.8 GPa and disappears at P ⩾ 8.6 GPa . Both A and ρ 0 values in Fermi liquid law ρ = ρ 0 + AT 2 at low temperature region increase abruptly above 4.8 GPa and exhibit a plateau at ∼ 9 GPa . These results suggest that non-magnetic state could be formed at P ⩾ 8.6 GPa and that possible quantum critical point might exist at pressures around 9 GPa in this compound. However, there is no sign of superconductivity in resistivity data at the lowest temperature we studied around the possible QCP.

Electrical resistivity measurements have been performed on the heavy fermion superconductor PrOs 4 Sb 12 between 0.3 and 300 K at pressures up to 9.8 GPa. Zero resistivity due to superconducting state was observed at all pressures up to P = 9.8 GPa. With increasing pressure up to 2.0 GPa, superconducting transition temperature T c was linearly shifted to lower temperature at a rate of − 0.16 K / GPa . Effect of pressure on T c became smaller on further pressurization, following that the value of T c was saturated to a constant value of 1.3 K at high pressure. While, the upper critical field H c 2 was strongly suppressed by increasing pressure. H c 2 at 9.8 GPa estimated from the onset temperature of superconducting transition was 0.91 T at 0.5 K.

The ferromagnetic compound Fe2P shows a first-order paramagnetic to ferromagnetic transition at TC=209 K. To investigate the magnetic properties of this compound under high pressures above 3 GPa, it has been tried to measure the magnetization using a diamond anvil type high-pressure apparatus by MPMS (quantum design). As the results of trial and error, we have succeeded to obtain the data with sufficient precision to understand the substantial behavior of the compound even under considerable high pressures above 5.0 GPa.

Enhancement-mode GaN-HEMT devices with a newly developed recessed-gate structure were fabricated. These devices were capable of operating at up to 30 MHz switching. A wireless power transmission (WPT) was adopted for a potential application of these GaN devices, because high-frequency (f) switching devices are expected to improve the power-transfer efficiency (η) of the WPT. A GaN-based E-class amplifier WPT system achieved 10W output power and η =63.5 % under the operating conditions of f =13.56 MHz, duty=50%, and a load resistance of 10Ω.

The pressure dependence of resistivity for the checkerboard-type charge-ordered (CO) molecular conductor $\ensuremath{\beta}\text{\ensuremath{-}}{(meso\text{-DMBEDT-TTF})}_{2}{\text{PF}}_{6}$ has been investigated. Under the low pressure of 0.6 kbar, the temperature of resistivity minimum $({T}_{\text{min}})$ falls from 90 K at an ambient pressure to 67 K, and after the resistivity has been increased, the superconducting (SC) transition is observed at 4.6 K. By applying magnetic field, the SC state is suppressed and the large positive magnetoresistance (MR) is demonstrated below ${T}_{\text{min}}$ in the CO state. Since the positive MR was observed even in the metallic state under high pressures, the summarized pressure-temperature $(P\ensuremath{-}T)$ phase diagram reveals that the SC state neighbors to the CO-insulating and charge-fluctuated metallic states.

The pressure ($p$) -- temperature ($T$) 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., Comment: 5 pages, 5 figures, to be published in J. Phys. Soc. Jpn

Atomic disorder is investigated for B2- and Heusler-phase CoFe1-xAlx alloys quenched from various temperatures by X-ray diffraction measurements. In the B2-phase region, with increase in quenching temperature, atomic disorder on the Co-site (Co-type disorder) proceeds for x=0.30 but not for x=0.70. In the Heusler-phase region (x=0.45, 0.50 and 0.55), atomic disorder between the Fe- and Al-sites (Fe-Al-type disorder) mainly proceeds. A relation between the magnetic behavior obtained in our previous work and the atomic disorder is examined. As a result, it is found that the Co-type disorder leads to a reduction of the magnetic moment in the B2-phase alloys and that the Fe-Al-type disorder does not significantly affect the magnetic behavior in the Heusler-phase alloys.

Magnetic behavior in Co-based Heusler alloys Co2MnZ (Z=Si, Ge, Sn) is investigated as a function of quenching temperature. The mean magnetic moment decreases with increase in quenching temperature in Co2MnSi and Co2MnGe while it remains almost constant in Co2MnSn. Relation between the magnetic behavior and the atomic disorder is discussed.The results of the lattice constant and the electrical resistance measurements are also reported.

Temperature dependence of time-resolved photoluminescence (PL) properties for rare-earth ions (REIs: Eu, Tb, and Er) implanted AlxGa1-xN (x=0∼1) is investigated. Thermal quenching for RE-related PL becomes small when increasing the Al contents. The PL decay time of REIs used in the present work becomes shorter when increasing the temperature and/or PL peak energy. The temperature dependence of PL intensity and the decay time are analysed by assuming phonon assisted energy-back-transfer model, in which the energy in REIs escape to trap levels. From the results, the improvement of PL properties can be well explained by the model, in which the activation energy for energy-back-transfer process is increased as increasing the Al contents.

We have performed the electrical resistivity measurements on Ce 2 RhIn 8 in the temperature range 0.3–300 K and observed zero-resistance state at ambient pressure on several samples. We have performed synchrotron X-ray diffraction experiment on single crystal of Ce 2 RhIn 8 to investigate relation between superconductivity and crystal structure. Superlattice reflections were observed with modulation wave vector q ∼(0, 0, 1/8) on the superconducting samples at room temperature.

Electrical resistivities of YbMn 2 Ge 2 were measured at several pressures in a temperature range from 2 K to room temperature. In low temperature region below 100 K, temperature dependence of the resistivity shows significant change between 2.0 and 4.0 GPa. Under 4.0 GPa, anomalies of the resistivity were observed at ( T t 3 ∼ ) 21.6 K and ( T t 4 ∼ ) 7.1 K. There is a fair possible that they originated from novel magnetic phase transitions of Yb or Mn sublattice. With increasing pressure, T t 4 increases linearly. In contrast to the pressure dependence of T t 4 , T t 3 decreases linearly.

SmCoIn 5 crystallizes in the tetragonal HoCoGa 5 type structure. This type of crystal structure have attracted much attention because new heavy-fermion superconductivity with very high superconducting transition temperature T c = 18.5 K was discovered in PuCoGa 5 . It is expected that Sm has a similar ground state to Pu compounds. Thus we have measured the electrical resistivity on a single crystal of SmCoIn 5 using a cubic anvil pressure cell at temperature 2–300 K under high pressure from 2 to 8 GPa. The value of T N that was 11.9 K at ambient pressure in SmCoIn 5 increased to 13.2 K at P = 2 GPa. Above 2 GPa, It decreased monotonously with increasing pressure and was 12.6 K at 8 GPa. It may be thought that the 4 f electrons in SmCoIn 5 are more localized than 5 f electrons in PuCoGa 5 .

We report the electrical resistivity and specific heat of the intermediate-valence intermetallic compound YbAl 2 . A single-crystalline YbAl 2 was synthesized by the Li-flux-growth technique. Electrical resistivity measurements were performed under high pressures up to 2.3 GPa. The value of the electrical resistivity increases with increasing pressure. This behavior is attributed to the gradual increase of the Yb valence in YbAl 2 .

We have performed an electrical resistivity measurement of the heavy fermion superconductor PrOs 4 Sb 12 under hydrostatic pressures up to 10 GPa and at temperature down to ∼2 K. As pressure was increased to 8 GPa, a roll-off behavior in ρ( T ) around 5 K attributed to the CEF effect was slightly shifted to higher temperature region with remaining its shape almost the same. At 9 and 10 GPa, T 2 -dependences of resistivity were observed below ∼5 K without showing a roll-off in ρ( T ). The obtained A values in ρ= ρ 0 + A T 2 at 9 and 10 GPa were 0.32 and 0.20 µΩcm/K 2 , respectively. This fact suggests that the CEF state of PrOs 4 Sb 12 might be drastically changed at P > 8 GPa.

Thermal neutron elastic scattering experiments revealed that iron localized moments form in an antiferromagentic short range ordering in LuFe 2 Ge 2 below 9 K. A long range type antiferromagnetic ordering grows rapidly under high pressure above 1.6 GPa.

A small hybrid CuBe/NiCrAl piston–cylinder-type high-pressure (HP) clamp cell was designed for low-temperature (LT) neutron diffraction (ND) measurements, and its characteristics was evaluated through various parameters which include cooling performance, transmission efficiency for neutrons. The cell successfully produces pressure up to 2.5 GPa at room temperature (RT).

We have performed AC calorimetric measurement under high pressure up to 1.56 GPa using a Cu–Be and Ni–Cr–Al hybrid piston cylinder cell in the temperature range from 2 to 12 K in CePd 2 Si 2 . It is clearly seen magnetic ordering temperature T N and magnetic contribution are suppressed under high pressures.

SmMIn5 ( M = Co , Rh , Ir ) crystallizes in the tetragonal HoCoGa5-type structure. This type of crystal structure is noticed as tetragonal variants of the AuCu 3 -structure, in which new superconductors were discovered. PuCoGa5 and PuRhGa5 are also the interesting superconductors. On the other hand, it is expected that Sm has a ground state similar to Pu compounds. We have succeeded in growing single crystals of SmMIn5 by the flux method. SmRhIn5 and SmIrIn5 showed the antiferromagnetic ordering and extra transitions below T N , which is almost same as the results in the previous report. We have succeeded in growing single crystals of SmCoIn5. It also showed the antiferromagnetic ordering and extra transitions below T N = 11.9 K . The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn5 compounds.

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.

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

Magnetic characteristics have been studied for a TbPd 2 Si 2 single crystal from measurements of magnetic susceptibility, high field magnetization, and specific heat. The antiferromagnetic ordering below T N =15 K has been confirmed. The easy magnetization direction is the [110] direction in the basal plane at high magnetic fields. The [110] magnetization is saturated above 24 T and reaches M s =9.0 µ B . Multistep metamagnetic behaviors appear in the basal plane magnetization processes. A one-step metamagnetic transition appears in the [001] magnetization process and persists up to 28 K above T N . Strong magnetic anisotropy is observed between the [110] and [100] directions for high fields, and between the [001] and directions in the basal plane. Magnetic phase diagrams are constructed, in which there are four magnetic ordered phases. The main features of anisotropic magnetic behaviors are almost explained by crystalline electric field effects.

Enhancement-mode m-plane AlGaN/GaN heterojunction field-effect transistors were fabricated with an Al2O3 gate dielectric deposited by atomic layer deposition (ALD). A threshold voltage of +3 V and an on/off ratio of 4×106 were obtained, demonstrating excellent subthreshold region characteristics. These results were achieved using non-polar m-plane GaN, Al2O3 as a gate dielectric, and a recessed-gate structure. The devices exhibited 138 mA/mm of maximum drain–source current at a gate–source voltage (Vgs) of +7 V and 45 mS/mm of maximum transconductance at Vgs=+5 V. The interface state density (Dit) of Al2O3 and m-plane GaN was measured using the photo assisted capacitance–voltage method, showing a Dit of (1–2)×1012 cm-2 eV-1. These results indicate the potential of Al2O3 deposited by ALD on m-plane GaN for power switching devices.

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.

Low ohmic contact resistance m-plane AlGaN/GaN heterojunction field-effect transistors were demonstrated using a regrown n+-GaN contact layer. An ohmic contact resistance of 0.25 Ωmm was obtained with an 80-nm-thick Si-doped regrown GaN contact layer deposited by metal organic chemical vapor deposition. Enhancement-mode m-plane AlGaN/GaN heterojunction field-effect transistors were demonstrated with a threshold voltage of +1.4 V and 2.0 mΩcm2 on-state resistances at +5 V of gate–source voltage.

The B-T magnetic phase diagrams for TbCu2Si2 single crystal, having the tetragonal ThCr2Si2-type crystal structure, have been constructed from magnetic measurements. The compound orders antiferromagneticaly below TN=11.9 K and shows another magnetic transition at Tt=9.1 K. In the easy magnetization direction of [110], a six-step metamagnetic process appears at low temperatures. Above Tt, it becomes a two-step metamagnetic one. There are seven ordered magnetic phases below the paramagnetic region in the B110-T magnetic phase diagram. In the [100] magnetization process, three metamagnetic transitions appear at low temperatures. The magnetization process becomes a one-step one above Tt. The B100-T phase diagram, composed of four phases, is very peculiar; a quad-critical point may appear. The magnetic structure for each phase has been discussed.

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...

Transistor operation was demonstrated on non-polar Si δ-doped m-plane AlGaN/GaN hetero-junction field effect transistors (HFETs) grown by metal organic chemical vapor phase deposition. A maximum drain–source current of 340 mA/mm at a gate–source voltage (Vgs) of +1 V, threshold voltage of -3 V and a maximum transconductance of 95 mS/mm at Vgs = -1.4 V were exhibited. With increasing Si δ-doping, the sheet carrier concentration increased from 3.1×1012 to 4.8×1012 cm-2. Good control of sheet carrier concentration by Si δ-doping was observed in non-polar m-plane AlGaN/GaN heterostructures.

The first demonstration of the m-plane AlGaN/GaN heterojunction field-effect transistor was reported. This transistor exhibited enhancement-mode operation, with the threshold voltage of +2.0 V owing to the nonpolar AlGaN/GaN heterojunction. The maximum drain–source current density and the maximum transconductance were 130 mA/mm at a gate–source voltage (Vgs) of +9 V and 25 mS/mm at Vgs = +8 V, respectively. The on-to-off ratio was over 106.

We report the results of investigation of the thermopower (Seebeck effect) of a ThCr2Si2-structured heavy fermion single-crystalline YbPd2Si2 compound (itterbium-palladium-silicon, 1-2-2) under ultra high pressure P up to 22 GPa. At ambient conditions the thermopower S was found to be negative. Under pressurization S inverted its sign and exhibited a bend near 6 GPa. The compressibility of YbPd2Si2 also showed a bend near 6 GPa corroborating a supposition about phase transformation.