[en] The triangular antiferromagnet CsFeBr₃, which has the spin singlet ground state due to the large single ion anisotropy of Fe²⁺ ions, shows the field-induced magnetic ordering for B||c. Submillimeter and millimeter wave ESR measurements of CsFeBr₃ have been performed at 2 K. Several absorption lines were observed below the ordering field 5 T which is in the paramagnetic region. Temperature dependence of ESR absorption lines for paramagnetic region shows the decrease of intensity as the temperature is increased. It suggests that the observed ESR absorption lines come from the ground state. Changes of the ESR modes at 2 K were observed at the field corresponding to the antiferromagnetic gap of 2.89 T. The results are discussed in connection with the theory of the gap system

[en] Recent advances in the high-field ESR studies of low-dimensional quantum spin systems in Kobe are presented. Among many systems studied, the results of S=((1)/(2)) quasi-one-dimensional (1D) antiferromagnet BaCu₂(Si_1-xGe_x)₂O₇ with the staggered field and S=((1)/(2)) diamond chain system Cu₃OH₂(CO₃)₂ are discussed. As the interchain interaction is almost canceled in the BaCu₂(Si_1-xGe_x)₂O₇ (x=0.65) system, we have found that the field and temperature dependences of the linewidth and the resonance field obey the Oshikawa-Affleck (OA) ESR theory of 1D antiferromagnet. The effect of the interchain interaction from the x dependence measurement and the existence of the breather mode at low temperature are also discussed. On the other hand, the high-field ESR measurements at 1.8 K revealed the direct transition in Cu₃OH₂(CO₃)₂. The direct transition turned out to be anisotropic and it will be discussed in connection with the ((1)/(3)) magnetization plateau which is also anisotropic

[en] We investigate electron spin resonance (ESR) on Cu benzoate, Cu(C₆H₅COO)₂·3H₂O, which is an ideal model substance of S=(1/2) antiferromagnetic Heisenberg chain (AFHC) with staggered field. Theoretically, S=(1/2) AFHC subjected to the staggered field exemplifies a good realization of a quantum sine-Gordon (SG) model. In fact, under magnetic fields, this compound develops an energy gap E_g(H) in the low-lying SG excitation spectra as a function of the applied magnetic field H. In the previous work, we observed the SG-breather excitation for the first time, in wide-field range up to 30 T by means of ESR under Faraday configuration. In this work, we report a direct observation of the SG-soliton/antisoliton excitation by ESR under Voigt configuration. Thus, all solutions of the SG equation are now experimentally demonstrated by means of ESR technique

[en] High-field ESR measurements were performed in Δ-chain compound [Cu(bpy)H₂O][Cu(bpy)(mal)H₂O](ClO₄)₂, which consists spin trimers with ferromagnetic and antiferromagnetic competing exchange interactions. A narrow EPR absorption line of Cu²⁺ and its anomalous temperature dependence were observed. The g-shift and frequency-dependent line width of this substance in the low-temperature region are discussed

[en] Azurite, Cu₃(OH)₂(CO₃)₂ is a candidate of the model substance for diamond chain with antiferromagnetic interaction. The millimeter and submillimeter wave ESR measurements of Cu₃(OH)₂(CO₃)₂ single crystal have been performed in the frequency region from 50 to 360 GHz and in the temperature region from 1.8 to 90 K. As the line width of ESR extends up to 3 T and it is impossible to observe by a conventional X-band ESR, the high field ESR measurement turned out to be essential. The g-shift was observed below 20 K, which corresponds to a peak of the magnetic susceptibility. Therefore, the development of the short range order may be the origin of the resonance shifts

[en] We report electron spin resonance (ESR) and magnetization measurements of the S=1/2 antiferromagnetic Heisenberg chain, Cu pyrimidine, [PM·Cu(NO₃)₂·(H₂O)₂]_n (PM=pyrimidine). The effect of staggered fields due to both the alternating g-tensor and the Dzyaloshinskii-Moriya interaction is clearly observed for the ESR line width and magnetization

[en] Submillimeter and millimeter wave ESR measurements of Cu₃(CO₃)₂(OH)₂ (azurite), which is the model substance for S=((1)/(2)) frustrated diamond chain, have been performed at 0.5 and 1.9 K. Anomalous AFMR modes, which cannot be interpreted as a simple two sublattice antiferromagnet, were observed at 0.5 K. The antiferromagnetic gaps at zero magnetic field were estimated to be 126 and 435 GHz for H//a and H//b, respectively. The observed AFMR mode is also discussed in connection with the magnetization result

[en] We report the in-situ investigation of electronic properties in yttrium (Y) hydride nanocontacts using a point-contact spectroscopy (PCS) technique, where hydrogen (H) atoms are absorbed at T ∼ 16 K. When a bias voltage is applied between both sides of Y nanocontacts immersed in liquid H₂, the differential conductance (dI/dV) spectra are changed largely due to H absorption in the nanocontacts. At the applied voltage of 350 mV, the V-shape anomaly appears at around zero bias in the dI/dV spectra. We conclude that the evolution of the spectra from Y metallic signal to V-shape is probably caused by a metal-insulator transition due to the phase transition from YH₂ to YH₃ from the comparison to the results of PCS experiments on Y-H nanocontacts prepared at high temperature. (author)

[en] We have developed a 9-mm-diameter "3He insert for precise magnetization measurements down to T = 0.4 K that is attachable to a commercial superconducting quantum interference device magnetometer. The insert is made from a thin-walled stainless steel pipe with an inner diameter of 6.2 mm, which determines the maximum sample size. "3He gas is condensed in the pipe, which is liquefied by "4He gas at T = 1.8 K generated by the magnetometer via the heat exchanger of a Cu vacuum jacket with an outer diameter of 8.6mm soldered to the stainless steel pipe. The temperature of the insert is decreased to T = 0.5 K by evacuating liquid "3He using a rotary pump and then to T = 0.36 K with a sorption pump. From the diamagnetization signal of a superconducting Al chip with a mass below 0.1 mg, the magnetization resolution with the insert is confirmed to be less than 10"−"7 emu. We measure the temperature dependence of magnetization down to T = 0.5 K in Pr_xLa_1_-_xPb_3, which is a good candidate for the reality of the quadrupolar Kondo effect, using the "3He insert. Non-Fermi liquid behavior of the nonlinear susceptibility in χ_3 with a -lnT dependence is detected in the [100] and [110] directions below T = 2.5 K, suggesting the screening of quadrupolar moments. In contrast, χ_3 in the [111] direction becomes constant below T = 3 K. The observed features indicate that a low-lying Γ_3 doublet plays a crucial role in the anomalous properties of Pr_xLa_1_-_xPb_3

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