Temperature and pressure variation of the 35Cl nuclear quadrupole resonance frequency in K2IrCl6

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Abstract
Experiments to study the temperature and pressure variations of the 35Cl nuclear quadrupole resonance (NQR) frequency in K2IrCl6 are described. The resonance frequency at atmospheric pressure is measured from 3.08 °K (the antiferromagnetic transition temperature) to 470 °K. Measurements of the pressure dependence of the resonance frequency for pressures to 5000 kg cm−2 have been carried out at five temperatures between 281 and 393 °K. A multiple-mode method is adapted to include the effect of the destruction of π bonding by the lattice vibrations and is then applied to the analysis of the temperature variation of the resonance frequency. The temperature dependence of the oscillation frequency of the rotary lattice mode is deduced. The behavior of the torsional oscillation frequency is nearly identical with that observed in K2PtCl6. An analysis of the combined results of the temperature and pressure studies in K2IrCl6 and similar results in K2PtCl6 suggest that volume effects as well as the destruction of π bonding may be important for the explanation of the experimental temperature dependence of the NQR frequency.