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Submillimeter and millimeter wave ESR measurements of one-dimensional CuO2 chain system Ca2Y2Cu5O10 have been performed using the pulsed magnetic field up to 16 T. The g-values are estimated to be g‖ = 2.31 and g⊥ = 2.03 from the powder pattern analysis. Obtained frequency-field diagram at 1.8 K is well described by an antiferromagnetic resonance mode with an uniaxial anisotropy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Submillimeter wave ESR measurements using the pulsed magnetic field is a powerful spectroscopic technique covering the wide frequency and magnetic field range with many advantages compared to the conventional X-band ESR measurements. Recent submillimeter wave ESR results showed that it is especially powerful to study the low dimensional antiferromagnets, that is, quantum spin systems. In accordance, the submillimeter wave ESR facilities in Japan are also presented. As an example of the study of quantum spin system, the investigation of the S=1/2 one dimensional antiferromagnets BaCu 2 (Si 1-x Ge x ) 2 O 7 (x=0, x=0.65), which have the staggered field effect in the system, is also presented in connection with the recent ESR theory by Oshikawa and Affleck (OA). Although both x=0 and x=0.65 systems show one dimensional behavior from the magnetic susceptibility, the temperature and frequency dependences of the mixed crystal x=0.65 system are well interpreted by the OA theory while they are not for the pure x=0 system. The antiferromagnetic resonance measurements of x=0 system (T N =8.9 K) have been performed up to 30 T at 1.8 K, and the magnetic phase transitions at 7 T and 16 T for H//α and H//c, respectively, are suggested for the first time.

High field ESR measurements of S =1/2 one-dimensional quantum antiferromagnetic (AF) system BaCu 2 (Si 1− x Ge x ) 2 O 7 have been performed using powder samples and pulsed magnetic field. High field electron paramagnetic resonance at 352 GHz and 86 K enabled us to determine the x dependence of g -values even when we used the powder samples. The x dependence will be discussed in connection with the crystal field. Moreover, antiferromagnetic resonances of x =0 and x =1 samples below T N were observed and their frequency–field relations suggest the existence of Dzyaloshinsky–Moriya interaction.

Recent advance of a field theoretical approach of a low-temperature electron spin resonance (ESR) in S=½ antiferromagnetic chain, which has Dzyaloshinskii-Moriya (DM) interactions and staggered g-tensor sites, by Oshikawa and Affleck (OA) suggests peculiar magnetic field dependence of ESR. Although BaCu 2 (Si 1 - x Ge x ) 2 O 7 is an antiferromagnetic chain system with mixed antiferromagnetic and ferromagnetic interchain interactions, we found that x=0.65 substance shows the peculiar field dependence of ESR predicted by OA theory. The temperature dependence of the line width showed the power-law dependence and strong field dependence in the gapless spinon regime which can be well interpreted by OA theory. The temperature dependence of the resonance shift turned out to be also consistent with OA theory. These results are also discussed in connection with Cu-Benzoate which is considered as a model substance of OA theory.

In the reproduced waveforms from thin film magnetic heads, distortions ("wiggles") are occasionally observed. In this study, a method for extracting wiggles from the reproduced waveform was devised, and the characteristics of wiggles were studied. The extracted wiggles had a pulse width of from 40 to 80 ns, and an amplitude of from 10 to 30 ?V Their positions in the reproduced waveform were shifted by an external magnetic field, but the wiggle width and amplitude were not affected. After awrite operation, the wiggle pulse width and amplitude changed; but, the area under the extracted pulses remained constant. Shifts in the peaks of reproduced waveforms increased when wiggles were close to the peak of the reproduced waveform, and the wiggle amplitude increased.

Submillimeter and millimeter wave ESR measurements of the one-dimensional CuO/sub 2/ chain system, Ca/sub 2/Y/sub 2/Cu/sub 5/O/sub 10/, have been performed using a pulsed magnetic field up to 16 T. The g-shift is observed between T/sub N/=30 K and 50 K. The frequency-field diagram observed at 1.8 K shows AFMR modes of the easy axis type, The magnetic properties of the AF (antiferromagnetic) state are discussed.

The distribution of magnetic field in the head gap and of flux density in in the magnetic path of thin‐film recording heads has been studied. It is shown that magnetic path saturation occurs first at the back end of the heads, which reduces efficiency. The relations which calculate the minimum current amplitude at magnetic path saturation are obtained. Results of the study are applied to thin‐film heads having two‐turn coils.