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Doping effect of nonmagnetic impurities, p-CyDOV-H (reduced form of p-CyDOV), on the organic spin-Peierls (SP) system,3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl (p-CyDOV) radical crystal, has been studied by measuring the temperature dependence of the magnetic susceptibility (T = 2.0-300 K) and the field dependence of the magnetization (H = 0-55 T) of the diluted p-CyDOV radical crystals, (p-CyDOV) 1 - x -(p-CyDOV-H) x (x = 0, 0.01. 0.03, 0.05, 0.07, and 0.10). The effect of doping on SP system is very remarkable. The SP transition temperature (Tsp = 15.0 K) decreases rapidly upon p-CyDOV-H doping and the SP state almost disappears in the lightly doped sample with x = 0.05. The susceptibility and magnetization of diluted radical crystal with x = 0.01 and 0.03 below T S P can be explained by the sum of the susceptibilities and magnetizations of the spin-Peierls state, antiferromagnet, and Curie impurity, respectively, indicating the coexistence of SP and antiferromagnetic phases in the doped SP system at low temperature. This work is the first report of the high-field magnetization study of the doping effect of nonmagnetic impurities on the organic SP transition system. more...

The specific heat, C, of single crystals of CuGe1−xSixO3 (x=0, 0.005, 0.008, 0.01, 0.015, 0.02, 0.027, 0.05) under magnetic field up to 15 T were measured and their magnetic phase diagrams were determined. The compounds with x⩽0.015 exhibit two transitions at TSP and TN in low magnetic field. An upturn of C/T for x=0.005 and 0.008 below ∼3 K originating from the AF ordering at lower temperatures is suppressed by magnetic field as in the case for x=0.01. However, the existence of M′ phase above ∼10 T which was observed for x=0.01 was not recognized for x=0.005 and 0.008, which suggests the existence of a critical x value for the appearance of M′ phase. more...

Magnetizations of spin-Peierls cuprates Cu 1- x Zn x GeO 3 with x =0, 0.005, 0.010, and 0.020 were measured in order to investigate influence of impurities on a magnetic phase. A characteristic change of the magnetization related to a phase transition from dimerized to other phases was seen below a spin-Peierls-transition temperature. The magnetization above 16.0 T shows weak x and temperature dependences. A critical field associated with the phase transition decreases with increasing x . We derived a result that the effects of impurities on the magnetic phase are weaker than on the dimerized phase. more...

Electron spin resonance (ESR) was investigated on the spin-Peierls system CuGeO3 and antiferromagnetic Ba2Cu3O4Cl2 at X-band and far-infrared regions (FIR). The g-values of CuGeO3 were determined to be 2.17, 2.26 and 2.11 for H∥a, H∥b and H∥c-axes, respectively. The temperature dependence of FIR and X-band ESR spectra of CuGeO3 clarified the difference of character among uniform, dimerize and high-field magnetic phases. In the Ba2Cu3O4Cl2 system, the resonance field for H∥c drastically changes around 30K, and antiferromagnetic resonance (AFMR) was observed at 5 K. more...

We measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cu 1− x Zn x GeO 3 with the x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed and it is associated with the phase transitions from the dimerized to the other phases. When the magnetic phase diagram is expressed by the reduced variables gH /2 T SP (0) and T / T SP (0), the phase diagrams of Cu 1− x Zn x GeO 3 qualitatively agree with those of organic spin-Peierls systems and the theoretical one. more...

The AC susceptibility in the cuprate compound CuGeO3, in which the spin-Peierls (SP) transition occurs around 14K in the absence of magnetic field, was measured in the magnetic field region up to 20 T to establish the magnetic phase diagram of CuGeO3. It was found that the isofield AC susceptibility shows a “knee” or peak at the phase boundary between the SP and uniform (U) phases and that between another magnetic (M) and U phases. The SP-M phase transition was clearly observed in the isothermal AC susceptibility. The determined phase diagram is consistent with the theoretical one after Cross and those of three organic SP materials. more...

ESR measurements have been performed in high magnetic fields up to 30 T on the spin-Peierls compounds CuGeO3 and MEM(TCNQ)2 to examine the magnetic excitation in the magnetic phase (M phase) induced by external fields. Discontinuous changes in the resonance fields have been observed around the phase boundary between the dimerized spin-Peierls phase and the M phase for both CuGeO3 and MEM(TCNQ)2. Anisotropic AFMR modes are observed in the M phase of CuGeO3. more...

We have performed the magnetoresistance measurements of two single crystals of FeSi in the temperature range 4.2–300 K. At 4.2 K the negative magnetoresistance is observed in sample K, which has less impurities judging from its resistivity, while the magnetoresistance of sample Y shows monotonical increase. The comparison of these two samples is discussed. more...

We measured the magnetization of Cu1−xMgxGeO3. A spin-Peierls-transition temperature and a critical field associated with a transition to a magnetic phase reduce up to x = 0.06. A spin-glass-like transition was not seen, although it was observed in Cu1−xZnxGeO3. The effects of substitution of Mg are weaker than those of Zn. more...

The ESR measurements of Co-based diluted magnetic semiconductors were carried out in the far-infrared range using pulsed high magnetic fields up to 30 T. The g-factor of Cd0.98Co0.02Te was determined to be g b *=2.294±0.003, and the zero-field splitting parameter 2D of Cd0.99Co0.01Se was directly determined to be 0.9±0.1 cm-1. These results were explained by the energy-level diagrams of a single Co2+ ion in a crystal field. more...