Anomalous Spin-Lattice Relaxation in Dilute RhFe at Positive and Negative Nanokelvin Spin Temperatures

Abstract

We have investigated at ultralow temperatures the spin-lattice relaxation in rhodium samples with about 10 p.p.m. of iron impurities. A strong decrease in the Korringa constant κ, dependent on the sign of the nuclear spin temperature T, was observed below 1 mT. Our data on the spin-lattice relaxation time τ1, measured at the electronic temperature Te = 120 μK, fit the equation 1/τ1 - 1/(κ0/Te) = 1/τimp1 (B, T), where the impurity term τimp1 (B, T) has a contribution proportional to the inverse nuclear spin temperature in small fields.