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The magnetic field of the high field ESR system in Kobe University has been extended to 55 T by using a new non-destructive pulse magnet and the 300 kJ (10kV) capacitor bank. The properties of new 55 T pulse magnet are reported. As an example of its application, the high field ESR measurement of a quantum spin system CsCuCl3 for H∥a will be shown.

We have developed a high field and high pressure ESR system including a unique pressure calibration method. We have succeeded in the ESR measurements up to 16 T under the pressure region up to 1.1 GPa. We will present about the ESR system and its application to a spin gap system KCuCl3. The energy gap between the singlet ground state and the triplet excited states are suppressed with applying pressure and the critical pressure of KCuCl3is estimated to be 0.90 GPa at 4.2 K.

Studies of novel quantum effects in quantum spin systems by high field ESR will be reviewed. High field ESR measurements of the Haldane system Y2BaNiO5 doped with nonmagnetic ion Mg2+have been performed. We have succeeded in resolving the ESR of finite Haldane chains using the high resolution feature of our high field ESR, and the direct information about the spin correlation in the Haldane chain at low temperature is obtained for the first time.

We report the cooperative phenomena of magneto-optical effect in AlN/GdN/AlN heterostructure grown by reactive rf magnetron sputtering technique performed under a base pressure less than 5×10−6 Pa. The ultra-high vacuum conditions during growth of GdN enable to curtail the oxophilicity character. The temperature dependent optical absorbance measurements have been carried out to evaluate the direct optical band gaps at the X point through the Tauc plots for the heterostructure. We observed for the first time that the optical absorbance studies demonstrate an exceptional splitting in valance and conduction bands in GdN below the critical temperature. The splitting energy is slightly increased with increase of temperature range of 30–55 K and the difference is merely ΔE=28 meV. Furthermore, the splitting energy drastically increases from 30 K to 3 K and the difference is ΔE=102 meV. This startling increase convincing that there is rapid increase of magnetic moments caused by long range correlation of spins.

Dolerophanite Cu2O(SO4) is one of model substances for S = 1/2 kagome like antiferromagnet. Although many X-ray diffraction studies have been performed on natural mineral Cu2O(SO4), little is known about its magnetic property. Therefore, the multi-frequency electron spin resonance (ESR) measurements of dolerophanite powder sample have been performed using pulsed magnetic fields up to 16 T in the frequency range from 50 GHz to 315 GHz in the temperature range from 1.8 K to 86 K Antiferromagnetic resonance (AFMR) has been observed below TN = 20 K, which is consistent with the previous magnetic susceptibility result by Asano et al. Moreover, the frequency-field relation at 1.8 K suggests typical easy-plane type AFMR with Dzyaloshinsky-Moriya (DM) interaction, which is also consistent with the weak ferromagnetism below TN suggested by Asano et al. As the estimation of DM interaction is very important to discuss the quantum phase transition in kagome antiferromagnet as suggested by C?pas et al. [2008, Phys. Rev. B 78 140405(R)], we have estimated the D term of DM interaction as 6.98 ? 0.01 K from our AFMR results.

High-field ESR measurements of cubic spinel GeCo2O4 single crystals have been performed using the pulsed magnetic field up to 16 T in the temperature range from 300 K to 1.8 K. Dynamical resonance shifts due to antiferromagnetic ordering were observed. New AFMR modes appear below 3 K. High-field ESR measurements reveal complicated phase structures and field-induced magnetic phases below TN, suggesting new temperature field phases.

We have developed high-field ESR system using commercially available SQUID magnetometer equipped with the superconducting magnet up to 5 T. This is a longitudinal magnetization detection type ESR. The minimum detectable spin number is evaluated as 2×1013 spins/G for 105 GHz. The most advantageous points as compared with other high-field ESR are that high-field ESR can be done very easily and both microscopic and macroscopic magnetic properties can be obtained at once. Moreover, the transmission technique without using cavity enables us to make multi-frequency ESR measurement in the wide frequency region. We have succeeded in observing ESR from 70 to 315 GHz.

High field ESR measurements of (2,3-dmpyH)2CuBr4 powder sample have been performed in the frequency range from 60 to 315 GHz using the pulsed magnetic field up to 16 T. Observed temperature range is 1.8 to 265 K. ESR spectrum observed at 265 K shows a typical powder pattern spectrum of Cu2+ ion, and obtained g-values are g// = 2.307 and g⊥ = 2.053. Temperature dependence measurements are also performed at 80, 160 and 315 GHz, and almost no temperature dependence of g-value is observed for all frequencies down to 1.8 K. These results are rather unusual for the low dimensional strongly correlated spin system, and possible mechanisms by spin frustration is suggested.

We have investigated the antiferromagnetic resonance modes of the kagome antiferromagnet Cs2Cu3SnF12 both theoretically and experimentally. High-field electron spin resonance experiments on single crystals were conducted in the ordered phase at different frequencies and temperatures with the external magnetic field parallel to the c axis. Considering three sublattices, we calculated the resonance modes for the motions of the sublattice magnetizations within the framework of the mean field approximation. It was found that the frequency-field diagram is in good agreement with the experimental results.

Specific-heat and magnetic susceptibility measurements were performed on the single-crystalline and polycrystalline samples of SmPd3S4. The magnetic susceptibility does not exhibit a cusp at the Neel temperature TN, which is commonly observed in antiferromagnets, but a first-order like discontinuous decrease below TN. One of the possible origins of a first-order like transition is a simultaneous occurrence of a magnetic-dipolar and a higher multipolar orders.

We have developed high-pressure, high-field and multi-frequency ESR apparatus. The pressure is available up to 14 kbar by using the clamped-type piston-cylinder pressure cell. All inner parts of the pressure cell are made of zirconia which has good transmittance of the electromagnetic wave in the frequency region from 70 to 700 GHz. The magnetic field region is up to 55 T and the temperature region is from 1.6 to 4.2 K. We present the results of quantum spin systems SrCu2(BO3)2 and CsCuCl3 as the application of this multi-extreme condition ESR technique and they will demonstrate its usefulness for studying the quantum spin system.

InMnO3 can be considered a model substance of the S=2 triangular lattice antiferromagnet from the crystal structure. As the magnetic susceptibility with a maximum around 15 K does not show a long-range order in spite of the large negative Weiss temperature of -430 K, spin frustration is expected to occur. We have performed the high-frequency high-field ESR of a powder sample InMnO3 in the frequency range of 70 to 360 GHz using the pulsed magnetic field up to 16 T together with the conventional X and Q-bamd ESR. The temperature dependence shows the g-shift and the broadening of the linewidth at low temperature, suggesting the development of spin correlation. Moreover, the frequency dependence measurement at 2.0 K suggests the existence of a spin gap. The spin gap is estimated to be about 26.5 GHz (1.2 K). The origin of the spin gap will be discussed in connection with the spin frustration in the system.

High-field ESR measurements of the novel Mn substance Bi3Mn4O12(NO3), which is a model substance of S=3/2 honeycomb lattice antiferromagnet, have been performed using the pulsed magnetic field up to 16 T. No resonance shift and the gapless behavior are observed in the temperature dependence measurements. Although, very strong antiferromagnetic interactions are expected from the Weiss temperature, there is no evidence of the long-range ordering down to 1.9 K from the magnetic susceptibility, the specific heat and the ESR measurements. Therefore, the existence of the frustration effect in Bi3Mn4O12(NO3) is strongly suggested in spite of the honeycomb lattice structure.

We report here the results of 51V-NMR experiments as well as susceptibility and high-filed magnetization measurements on a spin-1/2 honeycomb lattice antiferromagnet InCu2/3V1/3O3. The magnetization curve at 4.2 K showed no anomaly up to 54 T. A small anomaly around 38 K was found in the nuclear spin-latteice relaxation rate T−11 as well as the susceptibility, while NMR spectrum was temperature independent. Further, T−11 showed a broad maximum around 15 K and a tendency to be constant towards the lowest temperature of 2 K. Our results suggest that a large spin fluctuation remains until 2 K without a specific magnetic long-range ordering. Preliminary NMR results for an oriented sample are also shown.

In order to investigate the magnetic properties of GaAs:Er,O, we performed X-band ESR measurement on three different Er-concentration samples in the temperature region from T = 4.6 K to 18 K. Three types of Er-related ESR signals were observed below 18 K. The temperature dependence of the signal intensities and the result of the line shape analyses suggest that the luminescent related Er centers have a singlet-like ground state: that is, the Er-related centers are not homogenously distributed in GaAs:Er,O, and Er3+ ions can be antiferromagnetically coupled via the super exchange interaction. Moreover, we have shown that the Er-concentration dependence of intensities of ESR absorption has a strong correlation with the Er-concentration dependence of the PL intensities of GaAs:Er,O

Organic magnet [Ph(NH3)](18-crown-6)[Ni(dmit)2] is a candidate for an S = 1/2 two leg spin ladder system [S. Nishihara, T. Akutagawa, T. Hasegawa, and T. Nakamura, Chem. Commun. (Cambridge) 2002, 408.]. In order to investigate the non magnetic impurity effect for this compound, we performed X-band ESR measurement of [Ph(NH3)](18-crown-6)[Ni(dmit)2]1-x[Au(dmit)2]x. Non magnetic impurity concentration were estimated to be x = 0.029. ESR measurements have been performed from T = 4.5 K to 273 K using the Bruker ESR spectrometer. At T = 4.5 K, the fine structure ESR signals were observed. These signals suggest the existence of ferromagnetically coupled S = 1/2 dimers in the system.

High-field and high-pressure ESR measurements of SrCu2(BO3)2 have been performed at 1.6 K in the field region up to 30 T, the frequency region from 70 to 360 GHz and the pressure region up to 12 kbar. The direct ESR transition mode between the singlet ground state and the triplet excited states was observed at various pressures. We have succeeded in observing the decrease of the spin gap directly upon applying the pressure. The origin of the decrease of the gap energy is discussed.

Low-temperature magnetic properties of condensed matter system is investigated microscopically with high-frequency electron spin resonance (ESR). Experiments are carried out conventionally with a transmission method, but its sensitivity is not often sufficient to detect ESR signals of systems with small number of spins such as newly synthesized microcrystals. To attain better sensitivity, we focus on a novel technique of multi-frequency ESR system utilizing a microcantilever. In this method, ESR signal is detected as a torque change associated with the absorption of electromagnetic wave. Its sensitivity is greatly increased due to mechanical resonance when the modulation frequency of electromagnetic wave coincides with the eigenfrequency of the cantilever. In this study, we have succeeded in mechanical detection of ESR signals in the millimeter wave region up to 240 GHz. The achieved signal-to-noise ratio was greater than 103 for 1-μg sample of Co-Tutton salt, corresponding to the spin sensitivity of 109 spins/G.

The δ-chain, which consists of a sawtooth chain with frustrated spin trimers, is expected to have various ground state and low-lying excitations due to their geometrical spin network. The model substance of δ-chain compound is [Co2(OH){1,2,3-(O2C)3C6H3}(H2O)]·(H2O), which consists of Co2+ δ-chain. In this system Co2+ ion behaves like the Ising spin due to its magnetic anisotropy. To investigate the dynamical properties of this δ-chain compound, high frequency ESR measurements have been performed using Gunn oscillators and BWO. Observed dynamical property of [Co2(OH){1, 2,3- (O2C)3C6H3}(H2O)] · (H2O) will be discussed.

Magnetic properties of Cu3(OH)4SO4, which is a model substance of an S = 1/2 triple chain system, have been investigated by the magnetization and the high field ESR measurements. The magnetization measurements of powder sample have been performed up to 7 T at 2 K. The derivative magnetization curve shows a jump at 1.2 T due to a magnetic phase transition. The high field ESR measurements have been performed using the pulsed magnetic field up to 16 T in the temperature range from 1.8 K to 300 K. The resonance shifts due to low dimensionality are observed below 40 K far from TN = 5.3 K. The frequency-field diagram at 1.8 K below 5 T shows AFMR modes, which can be described by conventional AFMR theory of two sublattice with an uniaxial anisotropy, and the spin flop transition field is estimated to be 1.2 T. The ESR modes above 5 T deviate from the conventional AFMR modes.

X-band and high field electron spin resonance (ESR) measurements on S = 1/2 kagome lattice antiferromagnet Cu3V2O7(OH)2 2H2O (volborthite) have been performed. Although the kagome lattice is slightly deformed in the ab plane, no sign of magnetic order is observed down to 3.8 K, which is consistent with the magnetic susceptibility and the speciflc heat results, because the X-band ESR result shows no g-shift and the broadening of the linewidth down to 3.8 K. However, high field ESR results above 40 GHz show continuous g-shift below 20 K, which coincides with the broad maximum in the magnetic susceptibility. These results suggest the existence of the short range order and the field dependence in the system, and they are discussed in connection with the recent magnetization result.

We report the spin dynamics of the quantum kagome lattice ZnCu3(OH)6Cl2 observed by our high field ESR. The spin susceptibility deduced from our ESR result follows the Curie-Weiss-dependence, which is identical with the magnetic susceptibility. No resonance shift is observed down to 1.8 K in our measurement. This means that the internal field does not develop down to very low temperature. Moreover, the linewidth turns out to take the constant value from room temperature to 1.8 K. It suggests that the spin-spin correlation does not develop down to very low temperature of 0.009J. Our results suggest that ZnCu3(OH)6Cl2 looks like an ideal S = 1/2 kagome antiferromagnet from the ESR point of view.

Multi-frequency ESR measurements of S = 1/2 phyrochlore system ZnxCu4-x(OH)6Cl2(x = 0 ~ 0.5) have been performed using the pulse magnetic field up to 16 T and in the frequency region from 30 GHz to 360 GHz. Temperature dependence ESR measurement of the distorted pyrochlore system (x = 0) from 1.76 K to 265 K shows the linewidth broadening below 20 K, and the coexistence of AFMR modes and the peculiar mode is suggested below 6 K. Moreover, the x dependence measurements at 1.8 K suggest the existence of phase boundaries around x = 0.3 and 0.5. Possible model to interpret the result will be presented.