Magnetic excitations in the geometrically frustrated pyrochlore antiferromagnet Gd_2Sn_2O_7studied by electron spin resonance

摘要

The spin dynamics in the geometrically frustrated pyrochlore antiferromagnet Gd_2Sn_2O_7 is studied by means of the electron spin resonance. In the ordered phase (T_N=1 K), we have detected three gapped resonance modes. Their values agree well with the developed spin-wave theory which takes into account the Heisenberg nearest-neighbor exchange, the single-ion anisotropy, and the long-range dipolar interactions. The theory also predicts a fourth lowest-frequency gap, which lies beyond the experimental range of frequencies, but determines the exponential decrease in the specific heat at low temperature.