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Development of High Pressure, High Field and Multi-Frequency ESR System Using Hybrid Type Pressure Cell

T. Sakurai, H. Ohta, and Y. Uwatoko

Pressure has been recognized as one of the most important parameters to explore novel phenomena around the quantum critical point for quantum spin systems. As the high field and multi-frequency ESR is a powerful means to study quantum spin systems from the microscopic point of view, it is very useful to introduce the parameter of pressure to the ESR measurement. We developed the high pressure, high field and multi-frequency ESR apparatus by combining the single-pass transmission type ESR apparatus using the pulsed high magnetic field up to 55 T and the unique piston cylinder pressure cell previously [1]. The most characteristic feature of this pressure cell is that all inner parts are made of zirconium oxide which has relatively good transmittance of electromagnetic wave. It enables us to observe ESR under pressure. However, the pressure range is limited below 1 GPa at most because the single layer cylinder is used and its inner and outer diameters are 3 and 8 mm, respectively. The limited sample space also affects the signal intensity. The signal to noise ratio is not enough to study spin states in detail. Moreover, several compounds have been suggested to have the critical pressures above 2 GPa recently [2]. Therefore, the new ESR apparatus which has higher pressure range and sensitivity is required. In this study, we have developed new ESR apparatus which uses the combination of the hybrid type pressure cell and the superconducting magnet to improve these two points [3].

Fig. 1. Cut view of the hybrid type pressure cell for multi-frequency ESR measurement. Red lines show the electromagnetic wave.

Fig. 2. Pressure dependence ESR spectra of CsCuCl3 for H||c at 105 GHz.

Figure 1 shows the newly developed pressure cell for multi-frequency ESR measurement. The hybrid type cylinder which consists of inner NiCrAl cylinder and outer CuBe sleeve is used to achieve both larger sample space and higher pressure range above 2 GPa. The inner and outer diameters of the cylinder are 5 and 28 mm, respectively. The inner parts are all made of zirconium oxide. We confirmed that the pressure can be generated over 2.5 GPa at low temperature. However, they are sometimes cracked when the load is applied to generate the pressure over 2.5 GPa at low temperature. We have also developed new ESR apparatus using cryogen free superconducting magnet with wide bore. Gunn oscillator and backward wave oscillator which cover the frequency region from 50 to 400 GHz are used as the light source. The ESR signal is detected by an InSb detector and the signal is amplified by the lock-in technique. The larger sample space and the use of the lock-in technique make the sensitivity higher than previous apparatus successfully. Figure 2 shows typical ESR spectra obtained by the developed high pressure ESR apparatus. CsCuCl3 is a well known ABX3 type antiferromagnet with TN = 11 K. Figure 2 shows the antiferromagnetic resonance of this compound obtained at 4.2 K for H||c. It clearly shows that the resonance field shifts to the higher field side as the pressure is increased. This corresponds to the increase of the antiferromagnetic gap on applying the pressure [4]. The maximum pressure obtained in this measurement is 2.7 GPa as shown in Fig. 2. This result also shows that this high pressure ESR apparatus is promising tool to clarify the spin states of novel pressure induced phenomenon for quantum spin system.


References
  • [1] T. Sakurai et al., Rev. Sci. Instrum. 78, 065107 (2007).
  • [2] T. Sakurai et al., J. Phys. Conf. Ser. 150, 042171 (2009).
  • [3] K. Fujimoto et al., Appl. Magn. Reson. 44, 893 (2013).
  • [4] T. Sakurai et al., J. Phys. Conf. Ser. 215, 012184 (2010).
Authors
  • T. Sakuraia, S. Okuboa, H. Ohtaa, K. Matsubayashi, and Y. Uwatoko
  • aKobe University