Seisaku Imagawa

Electron Spin Resonance of Spin-Peierls Material CuGeO3

Magnetization and submillimeter wave ESR measurements have been performed on single crystals of CuGeO 3 using a pulsed high magnetic field. Magnetization jumps are observed at 12.8, 12.5 and 13.5 T for a -, b - and c -axes, respectively, at 4.2 K. The temperature dependences of the linewidth and the integrated intensity of the ESR signal are discussed in connection with the conventional spin-Peierls systems, and the excitation gap against the magnetic field is estimated when the field is applied along the a -axis. ESR has been observed in the magnetic phase above the critical field H c and the g -values have different values from those in the spin-Peierls phase. The origin of this difference is discussed.

Observation of Anomalous ESR Mode of CsCuCl3 in Submillimeter Wave Region

Submillimeter wave ESR has been performed from 90 to 380 GHz for CsCuCl 3 using the pulsed magnetic fields up to 15 T in the temperature range from 1.8 to 86 K. In the ordered phase below T N =10.5 K, shift of the ESR mode from that in the conventional mean field theory including Dzyaloshinsky-Moriya interaction has been observed for H // c above the critical field H c where a small jump in the magnetization occurs. These anomalies cannot be understood in terms of the mean field theory and will be discussed in connection with a new theory proposed by Shiba and Nikuni which suggests that the quantum effect is responsible for the anomalies at H c .

Magnetic Anisotropies of Fe/MgO Multilayers Determined by Submillimeter Wave FMR

The dependences of the resonance fields and the FMR absorption intensities of Fe/MgO multilayered films on the thickness of the Fe layer have been obtained by the submillimeter wave FMR using the pulsed magnetic field up to 15 T at 4.2 K. The magnetic anisotropy of each film, which is determined by the frequency dependence of the FMR with the aid of the results of the magnetization measurements, can explain the angular dependence of the FMR completely. The dependence of FMR absorption intensity on the thickness of Fe layer, however, turned out to be rather different from the results of the magnetization measurements.

ESR measurements of CsCuCl3 in high field phase

Abstract Submillimeter wave ESR measurements of CsCuCl3 have been performed at temperatures below TN = 10.5 K for H/c and H⊥c. For H/c a change of the ESR mode has been observed at a magnetic field around 12T, which corresponds to the field where a small magnetization jump occurs and it was interpreted as a quantum-fluctuation-induced magnetic phase transition proposed by Shiba and Nikuni. For H⊥c small absorption lines have been observed around 10 T together with the main absorption lines. These results will be discussed in connection with our calculated result and magnetization and neutron diffraction measurements.

ESR study of high and low field phases of spin-Peirls system CuGeO3

Abstract Submillimeter wave ESR of CuGeO3 has been performed. The resonances from both spin-Peierls (SP) and magnetic (M) phases have been observed in the 370 GHz band, and our results suggest different g-values for both phases. The temperature dependence of ESR from uniform (U) to SP phases also showed g-shift. The origin of these g-shifts is discussed.

Submillimeter wave esr and far infrared spectroscopy measurements of CuGeO3

Submillimeter wave ESR and far infrared transmission measurements of first inorganic spin-Peierls system CuGeO3 have been performed using the single crystals. Our new results are discussed in connection with the magnetic properties of the spin-Peierls systems and the recent neutron measurements of CuGeO3.

High field ESR of the spin-Peierls system CuGeO3

Abstract Submillimeter wave ESR measurements of single crystal CuGeO 3 , which has recently been found as the first inorganic compound which shows a spin-Peierls transition, have been performed in the frequency region from 90 to 380 GHz using a pulsed magnetic field up to 16T. The temperature dependences of the intensity and the line width in the temperature spin-Peierls system.

Electron paramagnetic resonance of CsCoxMg1-xCl3 and the determination of exchange interactions

The electron paramagnetic resonances of CsCo x Mg 1- x Cl 3 ( x =0.2, 0.4 and 0.6) have been observed at 220, 370, 585, 693.6 and 762.2 GHz in pulsed magnetic fields from 4.2 to 50 K. Paired spin excitations of intrachain and interchain pairs have been observed. Both intrachain and interchain exchange interactions are determined and our results suggest that there are at least two kinds of interchain exchange interactions in this system. The detailed analysis and the comparison of exchange interactions with those obtained by other measurements for CsCoCl 3 are discussed.

Anomalous spin-lattice relaxation of Cu2+ spins in CaO-P2O5 glasses under high magnetic field

Abstract Submillimeter-wave ESR and magnetization measurements have been performed on both CaO-P 2 O 5 glass and polycrystal with dilute Cu 2+ ions using a pulsed high magnetic field. An obvious difference in the intensity of the resonance absorption in increasing and decreasing magnetic fields has been observed in the 110 GHz ESR measurements of the glass, while it has not been found in the polycrystal. Time dependent hysteresis of the M - H curve has also been observed only in the glass. These anomalous relaxation phenomena are considered to be due to anomalous behavior of thermal properties observed in most amorphous materials at low temperature.

Submillimeter-Wave EPR of Cu2+ Spins in Ca(PO3)2 Glass

Submillimeter wave EPR spectra have been observed for Cu 2+ spin doped calcium metaphosphate Ca(PO 3 ) 2 glass by using a pulse high magnetic field. The EPR absorption curve obtained is similar to that of the powder pattern for the usual crystalline copper compounds. The absorption curve has been simulated by assuming the line shape, angular dependence of line width and parallel and perpendicular g -values. The g -values estimated are g // =2.44±0.02 and g ⊥ =2.07±0.01. Contribution to the line width of spin-spin, spin-lattice interactions and distribution of g -value are discussed from the dependence of spin concentration and temperature on the line width.