The divalent Eu intermetallic compound EuAl _4 with the BaAl _4 -type structure (space group: I4/mmm) orders antiferromagnetically at 16 K. Al atoms have two crystallographically inequivalent sites, denoted as Al(I) and Al(II). Three ^27 Al zero-field NMR spectra in the antiferromagnetic state of EuAl _4 at 4.2 K are detected in the vicinity of 12.8, 19.7 and 41.6 MHz, corresponding to the ^27 Al internal magnetic fields of 1.2, 1.8 and 3.7 T, respectively. The ^27 Al spectra at 12.8 and 19.7 MHz split into five resonance-lines because of the nuclear quadrupole interaction by I = 5/2. However, the ^27 Al spectrum at 41.6 MHz shows a broad line-shape. From analysis of these spectra, the ^27 Al spectra at 12.8 and 19.7 MHz correspond to those of the Al(II) site and the spectrum at 41.6 MHz belongs to that of the Al(I) site.

The electronic structure of CeNiSn, which is a potential topological Kondo insulator and a Dirac nodal -loop semimetal, has been investigated by employing temperature (T ) dependent angle-resolved photoemission spectroscopy (ARPES). The Fermi surfaces (FSs) and the band structures of CeNiSn for three orthogonal crystallographic planes are measured, in which both the very dispersive bands and the flat bands are observed, having mainly the Ni 3d character and the Ce 4 f character, respectively. The measured FSs and ARPES bands agree reasonably well with the density functional theory (DFT) calculations. The Fermi-edge (EF) photon energy (h nu) map along kb (= k(010)) shows that the metallic EF-crossing states on the (010) surface have the three-dimensional character, suggesting that the observed EF-crossing metallic states do not correspond to the topological surface states of the two-dimensional character. On the other hand, albeit weak, the features of the hourglass-type bulk band crossings are observed along SXS, with the energies and the slopes being similar to those predicted by the DFT calculations, supporting the Dirac semimetallic nature of CeNiSn. In T-dependent ARPES, the Ce 4 f Kondo resonance states are clearly revealed at low T, which become much suppressed above -80 K. This feature is consistent with the Kondo temperature of CeNiSn, estimated from its rho(T) data. This work demonstrates the importance of the coherent Kondo states in determining the topological properties of CeNiSn.

The thermal expansion of a diluted Ce system La1-x Ce x Cu6 for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis αb (T) suggests that the coupling between the 4f 1 electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn’t change by the substitution. Furthermore, the upturn in β m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

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. (C) 2021 Elsevier B.V. All rights reserved.

We report the results of muon spin relaxation (mu SR) and Si-29 NMR measurements carried out on the cubic chiral magnet EuPtSi. This compound exhibits a helimagnetic transition at T-N( )= 4 K, and hosts a unique skyrmion phase characterized by a short modulation period and strong anisotropy under magnetic fields. Our zero-field mu SR experiments revealed the development of critical slowing down of Eu spin fluctuations over a relatively wide critical region (T - T-N )/T-N < 5 above T-N. We also found from Si-29 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 have succeed in growing single crystals of EuCu and EuAu with the hexagonal structure by the Bridgman method. Both compounds are known to be ferromagnets with Curie temperatures and 13 K, respectively, and the Eu-4f magnetic moments of EuCu are known to orient along the hexagonal c-axis or the [0001] direction by the Mossbauer experiment. The magnetisations at 2 K in EuCu and EuAu in the present experiment saturate at an extremely low field of 2 kOe for , with a Eu-moment of . On the other hand, the hard-axis magnetisations for [0001] saturate at a high field of 40 kOe. It is also found from the electrical resistivty measurement that the electrical resistivities along the current [0001] in EuCu and EuAu are about at room temperature, which are compared with the resistivities of 30-40 for [0001]. The quasi-one dimensional conductivities are also characteristic, which were clarified from the de Haas-van Alphen (dHvA) experiment and FLAPW energy band calculation for EuAu, revealing the existence of a large plate-like Fermi surface.

We report 73Ge-NMR measurement on the ferromagnetic superconductor UGe2 at ambient pressure. The observed NMR spectrum supports that the electric field gradient at three inequivalent Ge sites is correctly deduced by a LDA calculation. The temperature dependences of the nuclear spin lattice relaxation rate 1/T1 for H0⊥a (easy axis) and H0∥a were obtained for the oriented sample. The contrasting behavior in 1/T1 for H0⊥a and H0∥a reveals that the magnetic fluctuation of UGe2 is highly anisotropic.

We grew high-quality single crystals of AuSb2 with the pyrite (FeS2)-type cubic structure by the Bridgman method and studied the Fermi surface properties by the de Haas-van Alphen (dHvA) experiment and the full potential LAPW band calculation. The Fermi surfaces of AuSb2 are found to be similar to those of NiSbS and PdBiSe with the ullmannite (NiSbS)-type cubic chiral structure because the crystal structures are similar each other and the number of valence electrons is the same between two different compounds. Note that each Fermi surface splits into two Fermi surfaces in NiSbS and PdBiSe, reflecting the non-centrosymmetric crystal structure.

In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors CeIrSi3 and CeRhSi3 carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in CeIrSi3 shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi3 does not possess a T = 0 quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in CeIrSi3 and CeRhSi3 and maybe in other heavy fermions.

$^{59}\mathrm{Co}$ 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.

EuCo2Ge2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Néel temperature TN=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.

In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature TN=66.5K. The magnetic structure below TN 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.