We have observed the double-spin-flip mode, corresponding to one photon fli
pping two nuclear spins, in rhodium with low-frequency SQUID NMR at ultralo
w temperatures. The shift and magnitude of the absorption line at around tw
ice the Larmor frequency has been studied. The shift of the double-spin-fli
p mode can be used to calculate the relative strength of the Ruderman-Kitte
l exchange interaction, for which we obtain R = - 0.9 +/- 0.1. (C) 2000 Els
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