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

Abstract

We report observation of the simultaneous excitation of nuclear and electronic spin waves by parallel pumping, an effect predicted by Ninio and Keffer, in ${\mathrm{RbMnF}}_3$ 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 $h_{\mathrm{rf}}$ 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, ${\eta }_k^n{\eta }_k^e{\text{\hspace{0.17em}=\hspace{0.17em}6.1×10}}^{10}\hspace{0.17em}{\sec }^{\text{−2}}$ for $\text{k→0}$ and ${\text{9.5×10}}^{10}\hspace{0.17em}{\sec }^{\text{−2}}$ for ${\text{k\hspace{0.17em}=\hspace{0.17em}1.05×10}}^5\hspace{0.17em}{\mathrm{cm}}^{\text{−1}}$ ($n$ stands for nuclear mode, $e$ for electronic). These figures are smaller by two orders of magnitude than what is obtained from ${\eta }_k^e$ inferred by Cole and Courtney from saturation of the main resonance and the value of ${\eta }^n$ 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 $h_{\mathrm{crit}}$ in the case of a flopped antiferromagnet.