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In this study, we investigate the magnetoelectric (ME) effect of the newly discovered antiferromagnetic (AFM) compound Ce$_{3}$TiBi$_{5}$ with a hexagonal structure (space group $P6_{3}$/$mcm$). In this system, Ce ions form zig-zag chains that extend along the $c$-axis. We focus on the lack of the local inversion symmetry at the Ce site, although the crystal structure has an inversion center. A theoretical study has predicted that magnetization can be induced by an electric current in the AFM ordering on the zig-zag chain. We conducted magnetization measurements on Ce$_{3}$TiBi$_{5}$ under an applied constant electric current and a static magnetic field around the AFM ordering temperature of $T_{\rm N}$ = 5.0 K. We successfully observed of the current-induced magnetization below $T_{\rm N}$. The magnitude of the current-induced magnetization has a linear electric current dependence and exhibits no magnetic field dependence. This behavior is consistent with the theoretical prediction of the ME effect in the ferrotoroidal ordered state., 11 pages, 5 figures

We have investigated whether or not superconductivity is induced by the application of pressure in very lightly F-doped LaFeAsO 1 − x F x , which shows spin density wave (SDW) state at ambient pressure, through the measurements of DC magnetization and electrical resistivity under pressure using pulse current sintered (PCS) high density polycrystalline specimens. It has been confirmed that the specimens with x = 0.025 shows superconductivity with T c dia ∼ 15 K under pressure above ∼ 1.3 GPa. The pressure induced superconductivity can be explained by the lattice compression along c-axis, which enhances the electron doping from LaO layers to FeAs layers.

We have succeeded in growing single crystals of hexagonal P 6 3 / mcm Ce3TiBi5 and orthorhombic Fmmm CeTi3Bi4 by the Bi self-flux method. Measurements of electrical resistivity, magnetic susceptibility, and specific heat have been made on Ce3TiBi5 and CeTi3Bi4. The results indicate that both Ce3TiBi5 and CeTi3Bi4 are new Ce compounds with an antiferromagnetic ordering temperature of 5.0 and 3.4 K, respectively.

We have performed parallel measurements of dc-magnetization and ac-magnetic susceptibility for a ferromagnetic superconductor, ${\mathrm{UGe}}_{2}$, in the ferromagnetic-superconducting phase. dc-magnetization measurements revealed that adequate demagnetizing of the sample allows for the preparation of various magnetized states with different zero-field residual magnetization. We observed that these states exhibit varying ac superconducting response at large ac-field amplitudes. The amount of ac flux penetration is less in the demagnetized state involving many domain walls. This result seems to contradict the theory that considers the domain walls as weak links. Moreover, the ferromagnetic domain walls enforce the shielding capability of superconductivity. This observation sheds light on the role of the domain walls on superconductivity, which has been a controversial issue for several decades. Two possible scenarios are presented to explain the enhancement of the shielding capability by the domain walls.

We have carried out $^{29}\mathrm{Si}$ nuclear magnetic resonance of ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$, which undergoes the so-called hidden order (HO) at ${T}_{\mathrm{HO}}=17.5$ K. The use of a $^{29}\mathrm{Si}$-enriched sample enabled us to obtain accurate NMR data up to 350 K and to extract the features of low energy magnetic correlations at high temperatures in this compound. Present results naturally indicate that ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ undergoes a crossover from localized to itinerant regimes with decreasing temperature and the HO occurs in the crossover region. We also discuss possible antiferromagnetic correlations remaining down to ${T}_{\mathrm{HO}}$ by extracting magnetic fluctuation components.

The amorphousization of Zr65Nb35alloy was performed. The Zr-Nb based alloys contained Al and Co elements were fabricated by arc-melting and melt-spinning methods. The superconducting property of the Zr(65-x)Nb35-xAlx(x = 0~15 at%) and Zr(65-x)Nb20Al15Coxalloys (x = 3~10 at%) was investigated by magnetic susceptibility measurements. The Zr(65-x)Nb20Al15Coxmetallic glasses (x = 6~10 at%) with superconducting nanocrystalline particles dispersed in an amorphous matrix exhibited a superconductivity below about 3.5 K. The addition of Co element led drastically to the amorphousization of the superconducting Zr65Nb20Al15alloy.

Experimental exploration of highly spin-polarized states of liquid 3He by applying external magnetic field is limited by the availability of static magnetic field. In the “ferromagnetic” superfluid A1 phase of liquid 3He there is an alternate method for boosting spin-polarization by the process of spin pumping without requiring such high magnetic field. The spin pumping in the A1 phase takes advantage of a superleak (SL) acting simultaneously as a filter for both entropy and spin. The spin pump technique that uses the SL-spin filter and a mechanical actuator enables us to directly boost polarization of 3He. The amount of enhancement of spin polarization has been limited so far. We are now developing a new type of SL filter made of packed aluminum oxide powder (referred as PAP-SL), in order to achieve greater enhancement of spin polarization. Several kinds of the PAP-SL filter were constructed by pressing aluminum oxide powders into a cylinder holder. The packed structures were carefully characterized by a flow-rate-measurement, X-ray tomography, and mercury intrusion porosimetry. The preliminary result shows that the PAP-SL works as SL filter for the superfluid 3He.

The Josephson effect between a single-crystal ${\mathrm{UPt}}_{3}$ and a conventional superconductor Al has been investigated under pressure for the junction on the ${\mathrm{UPt}}_{3}$ surface perpendicular to the hexagonal $c[0001]$ axis. Simultaneously measured magnetization has revealed that the Meissner fraction approaches a minimum value of $\ensuremath{\sim}1%$ at the critical pressure of ${P}_{\mathrm{c}}\ensuremath{\sim}0.4\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. The critical temperature ${T}_{\mathrm{c}}$ and the temperature ${T}_{\mathrm{J}}$ where a measurable Josephson critical current ${I}_{\mathrm{c}}$ first appears decrease with increasing pressure; the decreasing rate of $|d{T}_{\mathrm{c}}/dP|$ is almost constant, whereas $|d{T}_{\mathrm{J}}/dP|$ shows an abrupt increase above ${P}_{\mathrm{c}}$, indicating that the Josephson effect is suppressed above ${P}_{\mathrm{c}}$. These results, together with the decrease in penetration depth $\ensuremath{\lambda}$ derived from the magnetic-field dependence of ${I}_{\mathrm{c}}$, suggest that the superconducting phase is modified above ${P}_{\mathrm{c}}$ by the disappearance of the symmetry-breaking antiferromagnetic order.

The superconducting property of Zr 55 Co (30− x ) Al 15 Nb x ( x = 0–20 at.%) metallic glasses fabricated by rapid solidification was investigated. The Zr 55 Co (30– x ) Al 15 Nb x ( x = 5–20 at.%) metallic glasses with a mixture structure of amorphous and nanocrystal phases exhibited superconductivity of T c ,on = 1.8–2.6 K. The maximum T c ,on = 2.6 K was obtained for the Zr 55 Co 10 Al 15 Nb 20 metallic glass. This was attributable to the superconducting property of nanocrystalline particles contained in the Zr 55 Co 10 Al 15 Nb 20 alloy. The increase of Nb element in the Zr 55 Co (30– x ) Al 15 Nb x alloy led to the increase of T c ,on and the decrease of glass transition temperature. The glass transition temperature was between 704 and 749 K for the Zr 55 Co (30– x ) Al 15 Nb x ( x = 0–20 at.%) alloys. The temperature interval of supercooled liquid state was between 51 and 68 K for the Zr 55 Co (30– x ) Al 15 Nb x ( x = 0–20 at.%) alloys.

The superconducting property of Zr(1−x)Cox (x = 10–50 at.%) alloys and a Zr55Co30Al15 bulk metallic glass fabricated using techniques of rapid solidification was investigated. The Zr55Co30Al15 alloy crystallized by heat treatment in a vacuum atmosphere exhibited superconductivity of Tc,on = 2.4 K. This was attributable to the superconducting property of a crystalline Zr–Co alloy precipitated in the Zr55Co30Al15 alloy. The Tc,on of the crystalline Zr(1−x)Cox alloy was sensitive to the Co content. The increase of Co content for the Zr(1−x)Cox alloy led to the decrease of Tc,on. The Zr(1−x)Cox alloy exhibited superconductivity of a maximum Tc,on = 3.9 K for the Zr80Co20 alloy with superconducting nanocrystal particles embedded in the amorphous matrix.

We have been developing a micro superconducting quantum interference device (μ-SQUID) magnetometer for the study of quantum effects in μm- or nm-sized magnetic materials. In the μ-SQUID magnetometer, the sample is placed on the SQUID loop directly and the flux is detected by the loop itself. The close proximity between the sample and the SQUID loop is of great advantage for highly sensitive detection of magnetization from the tiny magnetic materials. However, the heat release during the operation of the SQUID could cause a great problem in experiments below 1 K because of the close proximity of the SQUID and sample. Here we report a digital circuit for the μ-SQUID magnetometer which can reduce the heat release in the low temperature operation and whose parts are commercially available. The circuit consists of a FPGA-digital board with analog-to-digital and digital-to-analog converters, and an independent pre-amplifier. By using this circuit we succeeded in measuring quantum tunneling of magnetization in the single molecule magnet, Mn12Ph at 0.7 K.

We have measured directional Compton profiles on the (001) plane in URu2Si2 single crystal at several temperatures. Two-dimensional electron occupation number densities (2D-EONDs) were obtained fro...

We report development of micro superconducting quantum interference device (μ-SQUID) magnetometers for investigation of quantum tunneling of magnetization in μm- and nm-size magnetic materials. Both high- and low-temperature superconductor (HTS and LTS) based μ-SQUID magnetometers were fabricated and a three dimensional magnetic coil system was constructed for this purpose. The HTS-μ-SQUIDs with a hole of 4×9 μm2 work at temperatures between 4.2 and 70 K and in magnetic fields up to 120 mT. A magnetization measurement of a ferrimagnetic micro-crystal was carried out at 35 K with an accuracy of 10−9 emu. The development of LTS-μ-SQUIDs has been started in order to study much smaller magnetic materials in a mK temperature range. We present a preliminary result on the LTS-μ-SQUID with a hole of 1×1 μm2. The critical current as a function of applied magnetic field shows the SQUID modulation at 4.2 K and up to 30 mT. The heat release associated with the present measurement method is estimated to be on the order of several microwatts.

The temperature dependence of electrical resistivitiy of Zr 55 Cu 30− X Al 10 Ni 5 Nb X (numbers indicate at.% X = 0, 1, 3 and 5) bulk metallic glasses was investigated below 300 K. For the Zr 55 Cu (30− X ) Al 10 Ni 5 Nb X alloys with X = 1, 3 and 5 consisting of nanocrystals dispersed in the amorphous matrix, the electrical resistivities decreased abruptly below approximately 2.3–2.9 K. For the amorphous Zr 55 Cu 30 Al 10 Ni 5 alloy, the electrical resistivitiy increased with decreasing temperature from 300 K up to approximately 2.0 K. The significant decrease of electrical resistivities of nanocrystal-dispersed amorphous alloys was attributable to the zero-resistivity effect of superconducting phases contained in the alloys. The Nb addition to Zr 55 Cu 30 Al 10 Ni 5 metallic glass was found to precipitate superconducting phases within the amorphous matrix.

We report the change of electronic structure associated with the hidden-order (HO) transition in ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ through Compton scattering experiment on the (001) plane of the single crystal. The two-dimensional electron occupation number densities (EONDs) obtained at 14 and 20 K, which are the projection of Fermi volume onto the ${k}_{x}\ensuremath{-}{k}_{y}$ plane of the first Brillouin zone, clearly reflect a whole image of electronic structure in the HO and paramagnetic (PM) phases, respectively. The change in electronic structure is well described by theoretical EONDs derived from the result of a band calculation, where $\mathrm{U}\phantom{\rule{0.28em}{0ex}}5f$ electrons are treated as itinerant ones. We also evaluate the electron (hole) numbers in the HO and PM phases and, therefore, its change on the HO transition. The HO transition is deeply involved with a significant change in $5f$ electrons from partially localized to itinerant states through hybridization with conduction electrons, resulting in the reconstruction of Fermi-surface structure.

We present a pressure-temperature phase diagram of URu 2 Si 2 consisting of four states; i.e., a superconducting state, a hidden ordered (HO) state, a large-moment antiferromagnetically (LMAF) orde...

The electron correlation in the 3d heavy-electron compound with linear spin chains, LaMn 4 Al 8 , has been investigated. Like a similar compound, YMn 4 Al 8 , we found a broad maximum in the temperature dependence of the susceptibility. This is interpreted by assuming the presence of a narrow pseudogap with the width Δ≃280 K in the spin excitation spectrum, which leads to the quenching of spin at low temperatures. Anomalies in susceptibility, resistivity and thermal expansion data, observed below approximately 50 K in spite of the absence of any phase transition, suggest the recovery of spin and the development of short-range magnetic correlation in this low-temperature range. This is in contrast to the case of YMn 4 Al 8 . No apparent long-range ordering in spite of the markedly developed magnetic correlation is probably due to the one-dimensional nature of the Mn spin arrangement.

We measured the ac magnetic susceptibility of the ferromagnet UGe 2 that exhibits superconductivity at high pressures within a ferromagnetic phase. It is known that the ferromagnetic phase is separated into two phases and thus there are two critical pressures, namely, P X ∼12 kbar at which an unknown phase transition terminates and P FM ∼16 kbar at which a Curie temperature is suppressed to zero. We observed the following features in the vicinity of P X : the discontinuity in the plot of superconducting transition temperature versus pressure, the maximum superconducting volume fraction in contrast to the small volume fraction near P FM , and the markedly enhanced initial slope of the upper critical magnetic field (exceeding 200 kOe/K). These results indicate that the superconductivity directly correlates with P X . We conclude therefore that it is the critical point P X , rather than P FM , that plays a crucial role in the appearance of the superconductivity.

We have made high pressure magnetization measurements on a single crystalline URu 2 Si 2 up to P = 1.61 GPa, in magnetic fields up to 15 T and in the temperature range between 4.2 and 100 K. A characteristic temperature T 0 which corresponds to an antiferromagnetic phase transition shows a slight increase with pressure, while T max , at which the temperature dependence of the magnetization exhibits a maximum, remains nearly constant with pressure. We have also observed that the pressure dependence of the high field magnetization at low temperatures shows a shallow minimum at around 1 GPa, in contrast to a strong and monotonic increase in a staggered magnetic moment revealed by recent elastic neutron diffraction experiments under pressures. To reconcile this discrepancy, we suggest, in conjunction with other experimental results, that the observed large staggered moment in the neutron diffraction experiments is not static but fluctuating in time.

We have measured the specific heat of a series of polycrystalline CePt 3 Si and Ce 1 + x Pt 3 + y Si 1 + z samples whose compositions vary slightly from the stoichiometric composition. We observed two peaks derived from magnetic anomalies on the specific heat measurements of the Ce 1 + x Pt 3 + y Si 1 + z samples. One of the peaks relates to the antiferromagnetic phase transition at T N = 2.2 K . The other is a large peak at 2.7 K observed for the sample that showed a ferromagnetic anomaly at 3.0 K on the temperature dependence of the magnetization. Heat treatment had different effects between these anomalies.

29 Si NMR experiments were performed to study microscopically the normal and superconducting states in 29 Si enriched CePt 3 Si. A 29 Si Knight shift parallel to the c-axis did not decrease below the T c . The 1 /T 1 result taken with a field cycling method showed no distinct coherence peak just below T c and a steep decrease below T c on cooling. The estimated value of the superconducting energy gap was about 2A = 3.6k B T c . These results may be an evidence for triplet pairing superconductivity.

In order to investigate a substitution effect and a heat treatment effect, we have prepared polycrystalline samples of CePt 3 - δ Si 1 + δ ( δ = - 0.05 ∼ 0.15 ) . We have carried out the DC and AC magnetic susceptibility on this system. It is found that the magnetic susceptibility at low temperatures is enhanced with increasing Pt concentration, and the magnetic susceptibility of quenched CePt 3 Si samples has two anomalies at T = 2.2 and 3 K. These anomalies are sensitive to the heat treatment and the substitution.

Elastic neutron scattering experiments on the pressure-induced ferromagnetic superconductor UGe 2 have been carried out under pressures P up to 1.6 GPa at temperatures T down to 60 mK, to study the correlation between superconductivity and ferromagnetism. No change was observed in ferromagnetic Bragg peak intensities nor a line width at Q = ( 0 , 0 , 1 ) through the superconducting transition temperature T SC under P ∼ 1.10 and 1.25 GPa, suggesting that the ferromagnetism is not affected by the onset of superconductivity under these two pressures.

In this article, we report the temperature dependence of spin-lattice relaxation rates at two Pt sites and one Si site in CePt 3 Si with a non-centrosymmetric structure center. 1 / T 1 for both Pt sites between 2 and 300 K and 1 / T 1 of Si above 3 K might be explained by the contributions from the low-lying crystal-electric-field level and the quasi-particle due to the hybridization between the ground state and conduction electrons. Just below T c no remarkable enhancement in 1 / T 1 was observed. The estimated value of superconducting gap is about 2 Δ = 3 k B T c .

The magnetization change ΔM at the superconducting transition of LaIrSi3 has been measured in various magnetic fields H. The observed ΔM in H = 0 is within the range of the Meissner effect induced by the possible residual field, suggesting that the spontaneous magnetization, if it exists, is below the experimental accuracy. This result is in agreement with the results of μSR experiments, in which no spontaneous magnetic field has been observed in the superconducting state.

We have measured the magnetization of two noncentrosymmetric superconductors: Ir2Ga9 and CePt3Si using a SQUID magnetometer, neither of which has been tested for the time-reversal symmetry in the superconducting state. For Ir2Ga9, the magnetization change ΔM below the superconducting transition temperature Tc ~ 2.2 K was smaller than 10-5 G in zero magnetic field, suggesting that ΔM originates in the Meissner effect induced by the possible residual field. When CePt3Si was cooled in zero magnetic field, ΔM along the c axis first decreased below Tc+ ~ 0.75 K (high-Tc phase) and then increased below Tc– ~ 0.45 K (bulk superconducting phase). Since this behavior cannot be explained by the Meissner effect, it may be a sign of a spontaneous magnetization.

High resolution Compton profiles have been measured in the single crystal of CeRu(2)Si(2) above and below the Kondo temperature to elucidate the change of the Ce-4f electron from localized to itinerant states. Two-dimensional electron occupation number densities projected on the first Brillouin zone, which are obtained after a series of analyses, clearly specify the difference between itinerant and localized states. The contribution of Ce-4f electrons to the electronic structure is discussed by contrast with a band calculation.

Measurements of specific heat between 80 mK to 4 K and electrical resistivity between 80 mK to 10 K were carried out for polycrystalline CePt3Si samples cut into small pieces (typically $\sim $10 mg). In the specific heat measurements, we observed an antiferromagnetic transition jump at TN = 2.2 K for all the samples, while the heights have large variations. As regards superconductivity, we observed two distinct transition jumps at Tcl $\sim$ 0.45 K and Tch $\sim$ 0.75 K, which were the same for all the samples. From the measurements of specific heat and resistivity, systematic relations were found between antiferromagnetic and superconducting transitions. We conclude that antiferromagnetism, whose transition temperature is 2.2 K, coexists with superconductivity, whose transition temperature is Tcl. In this sample, residual electronic specific heat coefficient in the superconducting state $\gamma_{\rm s}$ was quite small, and specific heat divided by temperature below Tcl decreased almost linearly with decreasing temperature. In order to reveal the characteristic properties of the magnetism and superconductivity of the CePt3Si system, it is important to study the two superconducting phases with Tcl and Tch, respectively., Comment: 5 pages, 4 figures

We have investigated the pressure dependence of ac and dc susceptibilities of the heavy-fermion superconductor CePt3Si (Tc= 0.75 K) that coexists with antiferromagnetism (TN = 2.2 K). As hydrostatic pressure is increased, Tc first decreases rapidly, then rather slowly near the critical pressure Pc = 0.6 GPa and shows a stronger decrease again at higher pressures, where Pc is the pressure at which TN becomes zero. A transition width and a difference in the two transition temperatures defined in the form of structures in the out-of-phase component of ac susceptibilities also become small near Pc, indicating that a double transition observed in CePt3Si is caused by some inhomogeneous property in the sample that leads to a spatial variation of local pressure. A sudden increase in the Meissner fraction above Pc suggests the influence of antiferromagnetism on superconductivity., 4 pages with 5 figures. This paper will be published in J. Phys. Soc. Jpn

The anomalous behavior of the heavy-fermion superconductor UBe13, which appears below the superconducting transition temperature Tc ∼ 0.9 K, has been investigated by point-contact spectroscopy and the Josephson effect. An abrupt increase in the temperature dependence of the Josephson critical current is observed below 0.7 K between UBe13 and conventional superconductors. The zero-bias resistance of the point contacts between UBe13 and Pt decreases continuously below Tc and shows an abrupt drop at 0.5–0.6 K. These results suggest that the anomaly originates from superconductivity rather than magnetism, which has been considered as one of the origins of the anomaly.

We have investigated the differential resistance of the point contacts between heavy-fermion superconductor UPt3 and a normal metal Pt, which were fabricated using a commercial piezo-electric actuator, and retried the observation of the energy gap of UPt3. A V-shaped dip is observed in both normal and superconducting states and disappeared around TK ~ 20 K, suggesting that it is related to the Kondo effect. Below the superconducting transition temperature, a shallow double-minimum structure, which indicates the energy gap, has been observed for the contacts on the faces perpendicular to the a-, b- and c-axes of UPt3.

We report magnetization of a non-centrosymmetric superconductor, LaPt3Si below 0.6 K up to 200 Oe. The home-made SQUID and Hall sensor magnetometers that operate below 1 K were constructed for this purpose. Although the SQUID magnetometer is more sensitive than the Hall sensor's one, it was found not to work correctly for the rapid magnetization change of LaPt3Si below 0.4 K. The Hall sensor magnetometer, in contrast, can properly detect magnetization jumps in the M–H curve of the superconducting state. The observed flux jumps are probably related to the interfusion of the mixed state of the LaPt3Si that is observed in the μSR measurements.

The design and fundamental properties of a small copper‐beryllium (CuBe) based piston‐cylinder‐type clamp cell for low‐temperature (LT) neutron diffraction (ND) measurements are reported. The results obtained for the superconducting ferromagnet UGe2 showed that the perfectly polarized ferromagnetic state is realized below Px.

We report the temperature ($T$) dependence of ferromagnetic Bragg peak intensities and dc magnetization of the superconducting ferromagnet UGe2 under pressure ($P$). We have found that the low-$T$ behavior of the uniform magnetization can be explained by a conventional Stoner model. A functional analysis of the data produces the following results: The ferromagnetic state below a critical pressure can be understood as the perfectly polarized state, in which heavy quasiparticles occupy only majority spin bands. A Stoner gap $\Delta(P)$ decreases monotonically with increasing pressure and increases linearly with magnetic field. We show that the present analysis based on the Stoner model is justified by a consistency check, i.e., comparison of density of states at the Fermi energy deduced from the analysis with observed electronic specific heat coeffieients. We also argue the influence of the ferromagnetism on the superconductivity., Comment: 5 pages, 4 figures. to be published in Phys. Rev. B

We have carried out thermal expansion measurements on the heavy fermion compound URu 2 Si 2 . We have discovered a new anomaly that appears only under pressure for both the tetragonal a and c axes. Plotting these temperatures on a temperature-pressure plane, we have constructed a phase diagram, in which there is a first order phase transition boundary separating a hidden and antiferromagnetic order. When the system enters the antiferromagnetic phase from the hidden order, the lattice constant shrinks along the a axis and elongates along the c axis, leading to an increase in the lattice constant ratio of c/a. We conclude that the system lies close to a bicritical point from which the first order phase transition line emanates.