Excitation of Nuclear and Electronic Spin Waves in RbMnF3 by Parallel Pumping

We report observation of the simultaneous excitation of nuclear and electronic spin waves by parallel pumping, an effect predicted by Ninio and Keffer, in RbMnF3 at a pumping frequency of 8.56 GHz. Wavevectors between near zero and 105 cm−1 are excited by varying H. We operate with H and hrf in a [100] direction and H greater than the value required for flopping. From threshold fields, which are about 1.2 Oe minimum, we calculate, at 4.2°K, ηknηke = 6.1×1010 sec−2 for k→0 and 9.5×1010 sec−2 for k = 1.05×105 cm−1 (n stands for nuclear mode, e for electronic). These figures are smaller by two orders of magnitude than what is obtained from ηke inferred by Cole and Courtney from saturation of the main resonance and the value of ηn taken from the half-width of NMR absorption. To reduce critical-field data to spin-wave linewidths we have applied the methods of Ninio and Keffer to obtain a theoretical expression for hcrit in the case of a flopped antiferromagnet.