Observation of a Nuclear-Magnon Contribution to the Nuclear Spin-Lattice Relaxation ofP191tin Ferromagnetic Cobalt

Abstract

We report the first indication for a nuclear spin-lattice relaxation mechanism originating from the coupling of the impurity nuclei to nuclear magnons. The magnetic hyperfine interaction and the nuclear spin-lattice relaxation of $^{191}P\mathrm{t}$ $({T}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.8\mathrm{d})$ in fcc Co were measured with NMR on oriented nuclei at temperatures between 8 and 14 mK in external magnetic fields ${B}_{\mathrm{ext}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.1--10\mathrm{kG}$. Between ${B}_{\mathrm{ext}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5$ and $1\mathrm{kG}$ the relaxation rate increases by 2 orders of magnitude. This increase is attributed to the interaction of ${}^{191}\mathrm{Pt}$ with nuclear magnons originating from the ${}^{59}\mathrm{Co}$ nuclear spin system.