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We have succeed in growing single crystals of EuCu5 and EuAu5 with the hexagonal structure by the Bridgman method. Both compounds are known to be ferromagnets with Curie temperatures TC=57 ...

Successive magnetic phase transitions at $T_{\text{N}}$=12.2 K, $T_{\text{N}}^{\;\prime}$=7.0 K, and $T_{\text{N}}^{\;*}$=5.0 K in EuIrGe$_3$, an intermetallic compound with a body centered tetragonal lattice belonging to a polar space group $I4mm$, has been investigated by neutron diffraction and resonant X-ray diffraction. It is shown that EuIrGe$_3$ exhibits an incommensurate longitudinal sinusoidal order with $q\sim (0, 0, 0.792)$ and $m_{q} \parallel c\text{-axis}$ in the high temperature phase ($T_{\text{N}}^{\;\prime}< T < T_{\text{N}}$), which changes to a cycloidal order with $q=(\delta', 0, 0.8)$ ($\delta'\sim 0.017$) and $m_{q} \parallel ac\text{-plane}$ in the intermediate phase ($T_{\text{N}}^{\;*} < T < T_{\text{N}}^{\;\prime}$). In the low temperature phase ($T < T_{\text{N}}^{\;*}$), the cycloidal plane rotates by $45^{\circ}$ to have $q=(\delta, \delta, 0.8)$ ($\delta\sim 0.012$). It is also pointed out that the X-ray scattering amplitude from odd-parity magnetic quadrupole due to the polar environment interfere with that from normal even-parity magnetic dipole in the magnetic ordered phase., Comment: 5 pages, 6 figures, 7 figures in the supplemental material, accepted for publication in J. Phys. Soc. Jpn

We carried out angle-resolved photoemission (ARPES) experiments using soft x rays to investigate the electronic structure of the intermediate-valence compound ${\mathrm{EuNi}}_{2}{\mathrm{P}}_{2}$. Both the ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}$ components arising from the $4{f}^{6}$ and $4{f}^{5}$ final states were observed in the valence spectra, directly confirming an intermediate-valence character of Eu ions. The three-dimensional band structure was studied by ARPES measurements, and the ARPES results were compared with calculations based on the density-functional theory for the non-4$f$ reference compounds ${\mathrm{SrNi}}_{2}{\mathrm{P}}_{2}$ and ${\mathrm{YNi}}_{2}{\mathrm{P}}_{2}$. We found that the ARPES spectra up to just below the Fermi level are better reproduced by the calculation of ${\mathrm{SrNi}}_{2}{\mathrm{P}}_{2}$ rather than that of ${\mathrm{YNi}}_{2}{\mathrm{P}}_{2}$. The heavy-fermion bands in ${\mathrm{EuNi}}_{2}{\mathrm{P}}_{2}$ are thus considered to be formed through the hybridization between the dispersive valence bands, which resemble those for ${\mathrm{SrNi}}_{2}{\mathrm{P}}_{2}$, and the ${\mathrm{Eu}}^{2+}$ components located at the very vicinity of the Fermi level.

A spin-polarized state is examined under charge current at room temperature without magnetic fields in chiral disilicide crystals NbSi_{2} and TaSi_{2}. We found that a long-range spin transport occurs over ten micrometers in these inorganic crystals. A distribution of crystalline grains of different handedness is obtained via location-sensitive electrical transport measurements. The sum rule holds in the conversion coefficient in the current-voltage characteristics. A diamagnetic nature of the crystals supports that the spin polarization is not due to localized electron spins but due to itinerant electron spins. A large difference in the strength of antisymmetric spin-orbit interaction associated with 4d electrons in Nb and 5d ones in Ta is oppositely correlated with that of the spin polarization. A robust protection of the spin polarization occurs over long distances in chiral crystals.

We report the results of muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) and $^{29}\mathrm{Si}$ NMR measurements carried out on the cubic chiral magnet EuPtSi. This compound exhibits a helimagnetic transition at ${T}_{\mathrm{N}}=4$ K, and hosts a unique skyrmion phase characterized by a short modulation period and strong anisotropy under magnetic fields. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ experiments revealed the development of critical slowing down of Eu spin fluctuations over a relatively wide critical region $(T\ensuremath{-}{T}_{\mathrm{N}})/{T}_{\mathrm{N}}l5$ above ${T}_{\mathrm{N}}$. We also found from $^{29}\mathrm{Si}$ NMR that the spin fluctuations are strongly suppressed by magnetic field in the paramagnetic state above 20 K. These characteristic spin dynamics observed over a wide region of temperature and magnetic field suggest the presence of magnetic frustration in the spin system. Such frustration would underlie the mechanism stabilizing the short-period skyrmion lattice observed in this compound.

We succeeded in growing single crystals of EuCuP with the hexagonal structure by the Sn-flux method and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, thermal expansion, and Hall effect, together with the electrical resistivity under pressure and magnetic field. EuCuP is a ferromagnet with a Curie temperature T C = 32 K, following a divalent electronic state, although the temperature dependence of the electrical resistivity is not simple but possesses a sharp and distinct peak at T C . The Curie temperature is found to increase continuously with increasing pressure P, with a large rate of d T C / d P = 5.7 K/GPa up to 8 GPa. This means that the divalent electronic state is stable up to 8 GPa. The present resistivity peak at T C is, however, extremely suppressed by magnetic field, and is found to be characteristic in a ferromagnet with a small number of carriers, which was confirmed from a measurement of the Hall effect.

In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Neel temperature T N = 66.5 K . The magnetic structure below T N was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo2P2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicate homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. We have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π/c to (0, 0, 0.73)2π/c, where c is the lattice parameter.

EuCo2Ge2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Neel temperature T N = 23 K. The magnetic easy-axis corresponds to the [100] direction (a-axis), while the [001] direction (c-axis) is a hard-axis. The magnetization for H ∥ [ 100 ] indicates a metamagnetic transition at 25 kOe and saturates above 75 kOe. On the other hand, the hard-axis magnetization increases approximately linearly and saturates above 110 kOe. The magnetic phase diagram was constructed. A characteristic feature in EuCo2Ge2 is known as a valence transition under pressure, from Eu 2 + δ to Eu 3 − δ ′ ( δ , δ ′ 1 ). We also clarified the valence transition by measuring the electrical resistivity under pressure. The valence transition occurs at 3 GPa, with a hysteresis, and terminates at about 4.5 GPa. Further increasing pressure, the electronic state is changed into a moderate heavy fermion state and approaches the nearly trivalent electronic state.

We have conducted 63,65Cu nuclear quadrupole resonance (NQR) measurements on A-site ordered perovskite compounds LaCu 3 Ru 4 O 12 and NdCu 3 Ru 4 O 12 to investigate their ground state and spin fluctuations. While there is only one Cu site in the crystal structure, multiple NQR resonance lines were observed. This is presumed to be due to the presence of slight distortion and lattice defects in the samples. The nuclear spin-lattice relaxation rate divided by temperature, 1 / T 1 T , for LaCu 3 Ru 4 O 12 showed almost constant value indicating the Fermi-liquid state. A remarkable increase in 1 / T 1 T due to spin fluctuations was observed in NdCu 3 Ru 4 O 12 . Furthermore, an evident magnetic phase transition at T M = 0.6 K was revealed from the distinct peak of 1 / T 1 T and the broadening of the NQR spectrum.

We grew high-quality single crystals of AuAl2, AuGa2, and AuIn2 with the fluorite (CaF2)-type cubic structure and determined the Fermi surface properties by the de Haas-van Alphen (dHvA) experiments using full-potential LAPW bad calculations. The Fermi surface and optical properties for three compounds were once studied from an interest of colors because AuAl2 has a striking bright reddish-purple color, whereas AuGa2 and AuIn2 are, respectively, neutral and bluish. The detected dHvA frequencies in the present study are found to be in a wide range of (0.1–13)×107 Oe. The main dHvA branches for three compounds are in excellent agreement with the theoretical ones, but some dHvA branches with small dHvA frequencies are slightly deviated from the theoretical ones, especially in AuGa2 and AuIn2.

A pressure-induced valence transition has attracted much attention in Eu-compounds. Among them, EuRh2Si2, EuNi2Ge2, and EuCo2Ge2 reveal the valence transition around 1, 2, and 3 GPa, respectively. We have succeeded in growing single crystals of EuT2X2 (T: transition metal, X: Si, Ge) and studied electronic properties under pressure. EuRh2Si2 indicates a first-order valence transition between 1 and 2 GPa, with a large and prominent hysteresis in the electrical resistivity. At higher pressures, the first-order valence transition changes to a cross-over regime with an intermediate valence state. Tuning of the valence state with pressure is reflected in a drastic change of the temperature dependence of the electrical resistivity in EuRh2Si2 single crystals. Effect of pressure on the valence states on EuRh2Si2, EuIr2Si2, EuNi2Ge2, and EuCo2Ge2, as well as an isostructural related compound EuGa4, are reviewed.

An extremely large magnetoresistance of PtSn4 has been recently observed and discussed from a viewpoint of de Haas-van Alphen (dHvA) oscillations and theoretical small Fermi surfaces. We have studied precisely the Fermi surfaces by measuring angular dependences of dHvA frequencies and have also carried out the full potential LAPW band calculation. Furthermore, small Fermi surfaces have been detected in another Pt-based compound of Pt3In7 with the cubic structure.

Multiple transition phenomena in divalent Eu compound EuAl$_4$ with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of $T_{\rm CDW}$ = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector $q_{\rm CDW}$=(0 0 ${\delta}_c$) with ${\delta}_c{\sim}$0.19. In contrast, magnetic peaks appear at $q_2 = ({\delta}_2 {\delta}_2 0)$ with ${\delta}_2$ = 0.085 in a magnetic-ordered phase at 13.5 K below $T_{\rm N1}$ = 15.4 K. By further cooling to below $T_{\rm N3}$ = 12.2 K, the magnetic ordering vector changes into $q_1 = ({\delta}_1 0 0)$ with ${\delta}_1$ = 0.17 at 11.5 K and slightly shifts to ${\delta}_1$ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at $T_{\rm N2}$=13.2 K and $T_{\rm N4}$=10.0 K. The structural modulation below $T_{\rm CDW}$ with $q_{\rm CDW}$ is characterized by the absence of the superlattice peak in the (0 0 $l$) axis. As a similar CDW transition was observed in SrAl$_4$, the structural modulation with $q_{\rm CDW}$ could be mainly ascribed to the displacement of Al ions within the tetragonal $ab$-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa$_4$. This could stem from different electronic structures with the CDW transition between two compounds., Comment: 6 pages, 3 figures, accepted for publication in J. Phys. Soc. Jpn

In this study, we measure the magnetic field and temperature variations of the magnetization \(M(H,T)\) of the cubic chiral compound EuPtSi and extensively investigate the magnetic phase transition...

We succeeded in growing single crystals of SrTGe 3 (T: transition metal) by the In-flux method and measured the electrical resistivity, specific heat, and de Haas–van Alphen (dHvA) effect. We confirmed superconductivity in SrPdGe 3 and SrPtGe 3 , which was previously observed using polycrystal samples, and also found superconductivity for SrRhGe 3 , SrIrGe 3 , and SrNiGe 3 . Furthermore, from the results of dHvA experiments and energy band calculations, Fermi surfaces of SrIrGe 3 are found to split into two similar Fermi surfaces, reflecting the Rashba-type non-centrosymmetric tetragonal structure. We also grew single crystals of EuTGe 3 by the same In-flux method and studied magnetic properties, especially focusing on magnetism of EuIrGe 3 with a Neel temperature T N =12.2 K and a successive magnetic transition T ' N =7.3 K. The magnetic phase diagram of EuIrGe 3 is found to consist of three antiferromagnetic phases named AF1, AF2, and AF3. A critical field H c reaching a saturated moment of 7 μ B /Eu is determined as H c ≃ 160 kOe from a high-field magnetization curve. We proposed a simple helical magnetic structure based on the Dzyaloshinskii-Moriya interaction.

We succeeded in growing single crystals of \(\hbox {Yb}_{4}\hbox {Sb}_{3}\), Ullmannite(NiSbS)-type compounds, \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\), EuPtSi, and EuPtGe with the non-centrosymmetric cubic structures by the Bridgman method. Split Fermi surface properties are clarified for \(\hbox {Yb}_{4}\hbox {Sb}_{3}\) and \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\). As for EuPtSi and EuPtGe with the cubic chiral structure, we observed the first-order like antiferromagnetic ordering at the Neel temperatures \(T_N=4.0\,{\rm K}\) and 3.4 K, respectively, which are small in magnitude compared with ordering temperatures of 10–100 K in the usual divalent Eu compounds, reflecting the frustration of spins in the chiral structure.

We have carried out angle-integrated photoemission spectroscopy (AIPES) and angle-resolved photoemission spectroscopy (ARPES) experiments using soft x rays on single crystals of ${\mathrm{EuCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{EuCu}}_{2}{\mathrm{Si}}_{2}$ grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in ${\mathrm{EuCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{EuCu}}_{2}{\mathrm{Si}}_{2}$ are in a divalent state and a nearly trivalent state, respectively, in accordance with the previously reported magnetic properties. The three-dimensional band structures and shapes of the Fermi surfaces of ${\mathrm{EuCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{EuCu}}_{2}{\mathrm{Si}}_{2}$ were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of ${\mathrm{EuCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{EuCu}}_{2}{\mathrm{Si}}_{2}$ are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for ${\mathrm{SrCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{YCu}}_{2}{\mathrm{Si}}_{2}$. This suggests that a charge transfer from the localized $4f$ states into the valence bands is responsible for the difference in the electronic states between ${\mathrm{EuCu}}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{EuCu}}_{2}{\mathrm{Si}}_{2}$.

The EuRu2P2 single crystal was investigated by means of magnetic, transport and thermodynamic studies at ambient and hydrostatic pressures. A small magnetocrystalline anisotropy with crystallographic [100] direction as an easy magnetization direction was found by experimental measurements and confirmed by first-principles calculations. We connect a previously reported change in the compressibility observed at room temperature to a rapid change of ordering temperature under applied hydrostatic pressure.

We grew single crystals of EuCo2P2 and EuT2Ge2 (T: Co, Rh, Ir, Ni, and Pd) by the Bridgman method and Sn- and In-flux methods, and studied their magnetic properties by measuring the specific heat, ...

We succeeded in growing single crystals of SrAl 4 and related compounds with the BaAl 4 -type tetragonal structure by the self-flux method, and measured the electrical resistivity, magnetic susceptibility, Hall coefficient, thermoelectric power, and de Haas–van Alphen (dHvA) effect. A plausible characteristic feature of the charge density wave (CDW) was observed below T CDW = 243 K in SrAl 4 . We also studied an effect of pressure on the electronic state in SrAl 4 by measuring the electrical resistivity and thermoelectric power. T CDW is found to decrease with increasing pressure, with a rate of dT CDW / dP = −12.5 K/GPa. To clarify the Fermi surface nesting, we studied the Fermi surface in SrAl 4 , which is found to be different from the Fermi surfaces of the similar compounds SrGa 4 , BaGa 4 , and BaAl 4 without CDW. The Fermi surfaces in these compounds were determined from the dHvA experiments, together with the energy band calculations.

Pressure is a powerful tool for exploring novel phenomena in solid-state physics. We review the electronic states of single-crystalline EuT2X2 (T: transition metal, X: Si or Ge) and related compoun...

The magnetic-field-induced A-phase for H ∥ [111] in cubic chiral antiferromagnet EuPtSi has been recently identified as a skyrmion lattice phase. We examined precise magnetic-field angle dependence...

The effect of pressure on the unique electronic state of the antiferromagnetic (AF) compound EuCu2Ge2 has been measured in a wide temperature range from 10 mK to 300 K by electrical resistivity measurements up to 10 GPa. The Neel temperature of TN = 15 K at ambient pressure increases monotonically with increasing pressure and becomes a maximum of TN = 27 K at 6.2 GPa but suddenly drops to zero at Pc = 6.5 GPa, suggesting the quantum critical point (QCP) of the valence transition of Eu from a nearly divalent state to that with trivalent weight. The rhomag0 and A values obtained from the low-temperature electrical resistivity based on the Fermi liquid relation of rhomag = rhomag0 + AT^2 exhibit huge and sharp peaks around Pc. The exponent n obtained from the power law dependence rhomag = rhomag0 + BT^n is clearly less than 1.5 at P = Pc = 6. 5 GPa, which is expected at the AF-QCP. These results indicate that Pc coincides with Pv, corresponding to the quantum criticality of the valence transition pressure Pv. The electronic specific heat coefficient, estimated from the generalized Kadowaki-Woods relation, is about 510 mJ/mol K^2 around Pc, suggesting the formation of a heavy-fermion state., 12 pages, 5 figures

EuPd3 is a rare Eu-based compound, whose Eu ions are in a trivalent state. The electronic structure of EuPd3 was investigated by angle-resolved photoemission spectroscopy (ARPES) using soft x rays....

We grew single crystals of EuCu2Si2 by the Bridgman and In-flux methods, and studied their crystallographic and magnetic properties precisely to clarify the ground state at low temperatures. The Br...

$^{59}\mathrm{Co}$ and $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements in external magnetic and zero magnetic fields have been performed to investigate the magnetic properties of the A-type antiferromagnetic (AFM) ${\mathrm{CaCo}}_{2}{\mathrm{P}}_{2}$. NMR data, especially the nuclear spin lattice relaxation rates $1/{T}_{1}$ exhibiting a clear peak, provide clear evidence for the AFM transition at a N\'eel temperature of ${T}_{\mathrm{N}}\ensuremath{\sim}110\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The magnetic fluctuations in the paramagnetic state were found to be three-dimensional ferromagnetic, suggesting ferromagnetic interaction between Co spins in the $\mathit{ab}$ plane characterizes the spin correlations in the paramagnetic state. In the AFM state below ${T}_{\mathrm{N}}$, we have observed $^{59}\mathrm{Co}$ and $^{31}\mathrm{P}$ NMR signals under zero magnetic field. From $^{59}\mathrm{Co}$ NMR data, the ordered magnetic moments of Co are found to be in $ab$ plane and are estimated to be 0.35 ${\ensuremath{\mu}}_{\mathrm{B}}$ at 4.2 K. Furthermore, the external field dependence of $^{59}\mathrm{Co}$ NMR spectrum in the AFM state suggests a very weak magnetic anisotropy of the Co ions and also provides microscopic evidence of canting the Co-ordered moments along the external magnetic field directions. The magnetic state of the Co ions in ${\mathrm{CaCo}}_{2}{\mathrm{P}}_{2}$ is well explained by the local-moment picture in the AFM state, although the system is metallic, as seen by $1/{T}_{1}T=\mathrm{constant}$ behavior.

We report $^{31}$P NMR measurements under various magnetic fields up to 7 T for the intermediate valence compound EuNi$_2$P$_2$, which shows heavy electronic states at low temperatures. In the high-temperature region above 40 K, the Knight shift followed the Curie--Weiss law reflecting localized $4f$ states. In addition, the behavior corresponding to the temperature variation of the average valence of Eu was observed in the nuclear spin-lattice relaxation rate $1/T_1$. With the occurrence of the Kondo effect, $1/T_1$ was clearly reduced below 40 K, and the Knight shift becomes almost constant at low temperatures. From these results, the formation of heavy quasiparticles by the hybridization of Eu $4f$ electrons and conduction electrons was clarified from microscopic viewpoints. Furthermore, a characteristic spin fluctuation was observed at low temperatures, which would be associated with valence fluctuations caused by the intermediate valence state of EuNi$_2$P$_2$., Comment: 7 pages, 5 figures