Simultaneous Parallel Pumping of Nuclear and Electronic Spin Waves

In a magnetic medium in which the nuclei carry a magnetic moment, there exists a spectrum of nuclear spin waves in addition to the usual electronic spin waves, provided the temperature is sufficiently low. The possibility is investigated of joint excitation of nuclear and electronic magnons by parallel pumping; this process is analogous to "exchange pumping" of acoustic and exchange magnons in a ferrimagnet. First a simple ferromagnet is considered, then the ferrimagnet manganese ferrite, and finally the cubic antiferromagnet RbMnF₃. It is suggested that the process should be feasible, and that it should be possible thereby to excite nuclear spin waves of arbitrary k. (In ordinary NMR only $k=0$ is excited.) The threshold pump field in a typical material is estimated to be of order 36 Oe in magnitude, but it can be smaller in carefully prepared samples.