S. Kimura

Millimeter and Submillimeter Wave ESR System: Using 30 T Pulsed Magnetic Field

New systems for millimeter and submillimeter wave ESR have been developed in Kobe University. In the previous system the pulsed magnetic field was limited up to 17 T in the temperature range from 1.8 to 86 K. Using the new systems, we can measure in the field range up to 30 T in the temperature range from 1.8 K to 4.2 K and from 18 K to room temperature. The resolution of the magnetic field has been also improved in the new ESR system. The details of our new ESR systems are presented. In addition, the measurements of Yb2Cu2O5 using these new systems are presented.

ESR study of Haldane system Y2BaNiO5 in submillimeter wave region

Abstract Submillimeter wave ESR of Haldane system Y 2 BaNiO 5 has been performed. The ESR absorption lines, which were observed in the temperature range above 15 K, are attributed to the transition between the excited triplet states. Frequency-field relations of these absorption lines are analyzed by the theory which explained those observed in NENP as the transitions between the excited triplet states near k = π.

Submillimeter wave ESR of S = 1 antiferromagnetic Heisenberg chain system with bond alternation

Abstract Submillimeter wave ESR of Ni 2 (μ-C 2 O 4 )(μ-N 3 )(Medpt) 2 (ClO 4 ) has been performed. A broad resonance has been observed above 10 K at 300 GHz for H ⊥ chain. We also have measured frequency dependence of the resonance. The energy gap and the anisotropy term DS 2 z of this system is discussed from our results.

Submillimeter-wave ESR measurements of low-dimensional quantum spin systems

Temperature-dependent electron spin resonance (ESR) measurements of two low-dimensional quantum spin systems, theS = 1/2 spin-ladder system Cu2(1,4-diazacycloheptane)2Cl4 (Cu2(C5H12N2)2Cl4) and the gaplessS = 1 bond-alternating one-dimensional antiferromagnettrans-Ni(333-tet)(N3)(ClO4), have been performed. X-band electron spin resonance (ESR) measurements of single-crystal Cu2(C5H12N2)2Cl4 show the increase of linewidth and anisotropicg-shifts below 8 K similar to those known for one-dimensional antiferromagnet. On the other hand, Ni(333-tet)(N3)(ClO4) has broad line-width and ESR has been observed for the first time by our high-field ESR. Its linewidth increases as the temperature is decreased, while theg-shift seems to be isotropic and theg-value decreases as the temperature is decreased. Thisg-shift can be connected to the quantum fluctuation of the system.

Submillimeter wave ESR measurements of gapless S=1 antiferromagnetic bond alternating chain system

Abstract Submillimeter wave ESR measurements have been performed on gapless S =1 antiferromagnetic bond alternating chain system Ni(333−tet)( μ −N 3 )(ClO 4 ) using the pulsed magnetic field up to 16 T and the resonance has been observed in the temperature region from 4.2 to 260 K for the first time. The g -shift and the broadening of ESR are observed below 113 K, which corresponds to the maximum of the magnetic susceptibility. These results suggest the importance of the quantum fluctuation in the system at low temperature.

Metamagnetic transitions of Lu2Cu2O5 studied by submillimeter-wave ESR measurement

Lu2Cu2O5 is a related substance of Y2Cu2O5 which is an unusual copper oxide with two successive metamagnetic transitions. We have performed the antiferromagnetic resonance (AFMR) measurements of Lu2Cu2O5 in the millimeter and submillimeter wave region with the pulsed magnetic field up to 16 T at 1.8 K. Our measurements this time are very detailed frequency dependence measurements compared to the previous measurement and we found new AFMR modes which were not observed previously. From the analysis of the observed AFMR modes, we found that the magnetic phase aboveHcl = 3.1 T in Lu2Cu2O5 is different from that in Y2Cu2O5.

ESR study of Mott—Hubbard insulators YTiO3 and LaTiO3 in submillimeter wave region

Abstract Submillimeter wave ESR of stoichiometric powder samples of Mott—Hubbard insulator RTiO 3 (R = Y, La) has been performed in the frequency region from 50 to 300 GHz. The EPR was observed for YTiO 3 at T > T c = 30 K and the nearly isotropic g -value 1.92 was obtained. The anisotropic FMR observed below T c for YTiO 3 . On the other hand, very weak EPR was observed at around g = 2 for LaTiO 3 at T > T N = 140 K, but we were not able to observe antiferromagnetic resonance below T N for LaTiO 3 .

High Field ESR System and Its Application to the Study of Quantum Spin Systems

Developments of the high field ESR system in Kobe University is presented. Using Gunn oscillators and backward traveling oscillators (BWO), we can cover the frequency region from 30 to 1183.6 GHz with the use of InSb detector. Pulsed magnetic field up to 30 T is available and we are now trying to extend the field up to 40 T. Temperature range is from 1.8 to 300 K. Using this system, we studied S=1/2 ladder like system Cu2(C5H12N2)2Cl4, and found a new magnetic transition at 10.1 T at 1.8 K. The temperature dependence of ESR in Cu2(C5H12N2)2CI4 shows g-shift below 8 K which corresponds to the maximum of the magnetic susceptibility. The g-shift below 8 K suggests the increase of the quantum fluctuation in the system, and the role of the quantum fluctuation in Cu2(C5H12N2)2CI4 is discussed.