Hikomitsu Kikuchi

Z2 Vortex-Induced Broadening of the EPR Linewidth in the Two-Dimensional Triangular Lattice Antiferromagnets, HCrO2 and LiCrO2

The title compounds are the family of the AMO 2 -type (R\bar3m) crystal which has a pronounced layer structure and are promising candidates for the two-dimensional Heisenberg triangular lattice antiferromagnet (2DH TAL-AF). The interesting observation is that a singular point of the EPR signal is located around T KM =0.66 J S 2 for the critical temperature of phase transition associated with the pairing-dissociation of the Z 2 vortices, suggesting the present system behaves as 2DH TAL-AF down to very close to T KM . The EPR linewidth exhibits Z 2 vortex-induced broadening above the critical temperature which is inversely proportional to the thermally excited vortex density, n v ∝exp (- E v / k B T ) with the activation energy \(E_{\text{v}}{\cong}4k_{\text{B}}T_{\text{KM}}\).

High Field ESR Study of the S=1/2 Diamond-Chain Substance Cu3(CO3)2(OH)2 up to the Magnetization Plateau Region

High field ESR measurements of Cu 3 (CO 3 ) 2 (OH) 2 have been performed in the frequency region from 50 to 900 GHz and in the temperature region from 1.8 to 265 K using the pulsed magnetic field up to 36 T. The large g -shifts below 23 K and the characteristic temperature dependence of the linewidth are discussed in connection with the two maxima of magnetic susceptibility observed at 5 and 23 K. Our ESR results together with the magnetization and theoretical results suggest that the ground state of the system is in the spin fluid (SF) phase at low field and low temperature. From the frequency–field dependence measurements at 1.8 K, the direct transition, which is closely related to the magnetization plateau from 16 to 26 T at 1.5 K, is observed for the first time. The observed frequency–field diagram suggests that the exchange interaction in the dimer is estimated to be about 50 K (1057 GHz).

Magnetic properties of the frustrated diamond chain compound Cu3(CO3)2(OH)2

Abstract Cu3(CO3)2(OH)2 (azurite), in which Cu 2+ (S= 1 2 ) monomers and dimers are arranged alternately along the b-axis to make an infinite chain, is regarded as an actual material for the frustrated diamond chain model. we have measured magnetic susceptibility, high field magnetization and 1 H NMR of a natural mineral single crystal of azurite to investigate the magnetic properties. The experimental results were compared with the theoretical expectation to suggest the ground state of Cu3(CO3)2(OH)2 is in a gapless phase.

High Field Magnetization of Quasi One Dimensional Ising Antiferromagnet CsCoCl3

Magnetization of quasi one dimensional Ising antiferromagnet CsCoCl 3 is measured at liquid 4 He temperatures in pulsed high magnetic fields. In the case of an applied field H parallel to the Ising c -axis, the magnetization M at liq. 4 He temperatures shows a metamagnetic transition which is characterized by the sharp double peaks of the field derivative of the magnetization d M /d H at 33.0 T and 43.9 T, respectively. The results are qualitatively explained by the Ising-like linear chain model with small antiferromagnetic inter-chain exchange interaction. The role of the inter-chain interaction is discussed within the framework of molecular field approximation. The temperature dependence and the transverse case of the magnetization process are also studied.

Magnetic properties of the diamond chain compound Cu3(CO3)2(OH)2

Azurite (Cu 3 (CO 3 ) 2 (OH) 2 ) is a model substance of a diamond spin chain, one of frustrated antiferromagnetic quantum spin chains. The high field magnetization up to 60 T, magnetic susceptibility, magnetic entropy, muon spin relaxation and 1 H-NMR of azurite have been measured using single crystals. A distinct 1/3 magnetization plateau is confirmed to be present in the magnetization curve. Two resonance peaks of 1 H-NMR. were observed. By analyzing temperature dependencies of their hyperfine shift. we found two different local susceptibilities which correspond to susceptibility of dimer and monomer spins, respectively. New field induced phase transition was found to occur at a critical field where the magnetic plateau onsets. A short range magnetic ordering developed in a peculiar two-stage process, which was revealed by temperature dependence of the magnetic specific heat and susceptibility.

Gd3+ EPR of High Temperature Superconductor GdBa2Cu3Ox

EPR measurements of Gd 3+ were performed in the superconducting and non-superconducting GdBa 2 Cu 3 O x . There is no distinct difference between the EPR behaviors of the two samples. The results show that even in the superconducting sample, the Gd ions behave as paramagnetic local moments with a mutual exchange interaction of 0.1 K.

Unconventional Colossal Magnetoresistance in Sodium Chromium Oxide with a Mixed‐Valence State

ions. This material demonstrates an unusual CMReffect that is closely related to its unconventional magneticstructure caused by spin frustration. The CMR of thiscompound is unique from several aspects. First, it is observedin a chromium oxide, not in a manganese oxide. Second, it isfound in a single-phase material having an insulating groundstate. Third, the CMR is not limited to the vicinity of themagnetic phase transition but becomes progressively moreprominent with decreasing temperature down to 0 K. Thediscovery of the NaCr

High Field ESR of Kagome Antiferromagnets SrCrxGa12-xO19.

High field ESR of Kagome antiferromagnets SrCr x Ga 12- x O 19 have been observed in the submillimeter wave region from 1.8 K to 265 K. The concentration dependence was observed from x =0.6 to x =8.78, and all samples showed the decrease of the resonance field and broadening of linewidth as the temperature was decreased. As the linewidth is very broad at low temperature, for instance about 7 T at 4.2 K, the measurement using high frequency was essential. The results are discussed in connection with the peculiar magnetic behaviors of the system observed by other measurements.

External magnetic field effects on a distorted kagome antiferromagnet

We report bulk magnetization, and elastic and inelastic neutron scattering measurements under an external magnetic field H on the weakly coupled distorted kagome system, Cu2(OD)3Cl. Our results show that the ordered state below 6.7 K is a canted antiferromagnet and consists of large antiferromagnetic ac components and smaller ferromagnetic b components. By first-principles calculations and linear spin wave analysis, we present a simple spin Hamiltonian with nonuniform nearest neighbor exchange interactions resulting in a system of coupled spin trimers with a single-ion anisotropy that can qualitatively reproduce the spin dynamics of Cu2(OD)3Cl.

High Field Phase Transitions of Quasi One-Dimensional S= 1/ 2 Heisenberg Antiferromagnet Cu 2(1,4-diazacycloheptane) 2Cl 4 Observed by Submillimeter Wave ESR

Millimeter and submillimeter wave ESR measurements on a single crystal of an S =1/2 Heisenberg ladder-like system Cu 2 (C 5 H 12 N 2 ) 2 Cl 4 have been performed using a pulsed magnetic field up to 16 T. The gap is estimated to be 9.7 K from the temperature dependence of ESR intensity. The detailed frequency dependence of ESR in the frequency region from 40 to 420 GHz at 1.8 K suggests magnetic transitions at H c1 =7.5 T, H c2 =10.1 T and H s =13.2 T. A transition at 10.1 T is suggested for the first time. These results are discussed with previous magnetization measurements and theoretical calculations, and our results appear to be difficult to interpret according to the simple ladder model.