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We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution regi...

High-pressure and high-field electron spin resonance (ESR) measurements have been performed on a single crystal of the orthogonal-dimer spin system SrCu$_{2}$(BO$_{3}$)$_{2}$. With frequencies below 1 THz, ESR signals associated with transitions from the singlet ground state to the one-triplet excited states and the two-triplet bound state were observed at pressures up to 2.1 GPa. We obtained directly the pressure dependence of the gap energies, finding a clear first-order phase transition at $P_{c}=1.85\pm0.05$ GPa. By comparing this pressure dependence with the calculated excitation energies obtained from an exact diagonalization, we determined the precise pressure dependence for inter- ($J'$) and intra-dimer ($J$) exchange interactions considering the Dzyaloshinski-Moriya interaction. Thus this system undergoes a first-order quantum phase transition from the dimer singlet phase to a plaquette singlet phase above the ratio $(J'/J)_{c}=0.660\pm0.003$.

We have developed a low-temperature ESR system under pressure, which has the frequency region above 70 GHz, the pulsed magnetic field up to 16 T and the pressure region up to about 3.5 kbar. A suitable pressure-calibration method using the change of the ESR of ruby under pressure has been also developed. We can determine the pressure and observe ESR signals of a sample at the same time. The high-field ESR measurements with the pulsed magnetic field up to 16 T have been performed on triangular antiferromagnet CsCuCl 3 for H||c around 6 K at 1 bar and at 3.1 ± 0.6 kbar in the frequency region from 120 GHz to 370 GHz. We observed the increase of the phase transition field from the umbrella-type configuration to the coplanar configuration due to the quantum fluctuation and the increase of the antiferromagnetic gap under pressure. The possible origin of this increase of the phase transition field was discussed in connection with the recent magnetization measurements under pressure.

X-band and millimeter wave ESR measurements have been performed on (DI-DCNQI) 2 Ag single crystals. X-band ESR measurements were carried out with the static magnetic field up to 1 T. Electron param...

Magnetization, specific heat, and electrical resistivity measurements have been performed for polycrystalline samples of hexagonal CeRh6Ge4 and CeRh6Si4. The Ce ions in CeRh6Ge4 are trivalent above 100 K, while those in CeRh6Si4 display an intermediate-valence state below room temperature. We discovered that CeRh6Ge4 is a new ferromagnetic (FM) compound with the transition temperature TC = 2.5 K. The −lnT dependence of the magnetic part of the electrical resistivity, the small magnetic entropy released at TC (0.19Rln2), and the relatively large electronic specific-heat coefficient (0.25 J·mol−1·K−2) imply that CeRh6Ge4 is a Kondo-lattice compound. We argue that CeRh6Ge4 is a rare Ce-based FM compound with a proximity to a quantum critical point.

We report on the discovery of ferromagnetic behavior below \(T_{\text{C}} = 41\) K in CeIr3B2 single crystals by means of magnetization, electrical resistivity, and specific heat measurements. The ferromagnetic transition temperature is unusually high despite the lack of magnetic elements except Ce, which is the second highest transition temperature recorded after CeRh3B2 (\(T_{\text{C}}\sim 120\) K). The ferromagnetic ordered moment is estimated to be \(\mu_{\text{s}}\sim 0.04\) \(\mu_{\text{B}}\)/Ce at 1.8 K, which lies in the \(c\)-plane of a monoclinic crystal structure. A structural phase transition from monoclinic to hexagonal occurs approximately at 395 K upon heating. The similarity and difference in physical properties between CeIr3B2 and CeRh3B2 are discussed.

A single-crystalline sample of the tetragonal rare-earth ferromagnet CeRu2Al2B has been grown and its magnetization measurements have been performed. The highly anisotropic magnetic susceptibilities with the \(c\)-axis being the magnetic easy axis can be explained by considering the \(4f\) levels with the Γ\(_{7}^{(1)}\) doublet ground state. A temperature vs magnetic-field (\(T\)–\(B\)) phase diagram along the \(a\)-axis has been constructed. The appearance of two ferromagnetic phases in the \(T\)–\(B\) phase diagram and a reduced spontaneous magnetization along the \(c\)-axis support the previously proposed magnetic state that the magnetic structure of ferromagnetic state is not a simple Ising-like structure along the \(c\)-axis but a canted structure having antiferromagnetic components in the \(c\)-plane.

Measurements of magnetization were performed on polycrystalline samples of Sm 1- x T x Pd 3 S 4 and Tb 1- x T x Pd 3 S 4 (T = Y and Gd) to examine the origin of first-order-like antiferromagnetic (AFM) transition in SmPd 3 S 4 and TbPd 3 S 4 . With increasing Y (Gd) concentration, the AFM transition temperatures for both Sm 1- x T x Pd 3 S 4 and Tb 1- x T x Pd 3 S 4 decrease (increases) monotonically. First-order AFM transitions observed in SmPd 3 S 4 and TbPd 3 S 4 change into second-order ones by Gd substitution. Such a change in the order of transition implies that a contribution of magnetic interaction to the AFM transition overcomes that of multipolar interaction in Gd-rich compounds.

High-frequency ESR results on the S=1/2 Heisenberg hexagonal antiferromagnet InCu2/3V1/3O3 are reported. This compound appears to be a rare model substance for the honeycomb lattice antiferromagnet with very weak interlayer couplings. The high-temperature magnetic susceptibility can be interpreted by the S=1/2 honeycomb lattice antiferromagnet, and it shows a magnetic-order-like anomaly at TN=38 K. Although, the resonance field of our high-frequency ESR shows the typical behavior of the antiferromagnetic resonance, the linewidth of our high-frequency ESR continues to increase below TN, while it tends to decrease as the temperature in a conventional three-dimensional antiferromagnet decreases. In general, a honeycomb lattice antiferromagnet is expected to show a simple antiferromagnetic order similar to that of a square lattice antiferromagnet theoretically because both antiferromagnets are bipartite lattices. However, we suggest that the observed anomalous spin dynamics below TN is the peculiar feature of the honeycomb lattice antiferromagnet that is not observed in the square lattice antiferromagnet., Comment: 5 pages, 5 figures

High-field electron spin resonance (ESR) measurements have been performed on vesignieite BaCu$_3$V$_2$O$_8$(OH)$_2$, which is considered as a nearly ideal model substance of $S$=1/2 kagome antiferromagnet, in the temperature region from 1.9 to 265 K. The frequency region is from 60 to 360 GHz and the applied pulsed magnetic field is up to 16 T. Observed g-value and linewidth show the increase below 20 K, which suggest the development of the short range order. Moreover, a gapless spin liquid ground state is suggested from the frequency-field relation at 1.9 K., Comment: 5 pages, 6 figures, jpsj2 class file, to be published in J. Phys. Soc. Jpn

High-field electron spin resonance (ESR) measurements of single crystals of (CH 3 ) 2 NH 2 CuCl 3 (DMACuCl 3 ) have been performed in the frequency range of 50 to 550 GHz in the paramagnetic region. In addition to the electron paramagnetic resonance, we have observed four ESR modes ω 1 , ω 2 , ω 3 , and ω 4 . The modes ω 2 and ω 3 have a frequency gap of 325 GHz (15.6 K), while the mode ω 1 has a gap of 420 GHz (20 K) at 0 T. The modes ω 2 and ω 3 are attributed to the transitions between the singlet and the triplet of the antiferromagnetic (AF) dimer. We found that the large spin-gap for the AF dimer still remains at the critical field B c2 = 3.5 T determined by magnetization and specific heat measurements.