$^{235}$U nuclear relaxation rates in an itinerant antiferromagnet USb$_2$

TL;DR

This study investigates the nuclear relaxation rates of $^{235}$U in USb$_2$, revealing a common relaxation mechanism for uranium and antimony nuclei with a power-law temperature dependence and an anomaly at 5 K.

Contribution

First measurement of $^{235}$U nuclear relaxation rates in USb$_2$, overcoming experimental challenges to reveal relaxation mechanisms in an itinerant antiferromagnet.

Findings

$^{235}$U and $^{121}$Sb relaxation rates follow a $T^{0.3}$ power law.

An anomaly at 5 K suggests a change in hyperfine interactions.

Successful indirect measurement of $^{235}$U $T_1^{-1}$ despite heating effects.

Abstract

$^{235}$U nuclear spin-lattice ($T_1^{-1}$) and spin-spin ($T_2^{-1}$) relaxation rates in the itinerant antiferromagnet USb$_2$ are reported as a function of temperature in zero field. The heating effect from the intense rf pulses that are necessary for the $^{235}$U NMR results in unusual complex thermal recovery of the nuclear magnetization which does not allow measuring $T_1^{-1}$ directly. By implementing an indirect method, however, we successfully extracted $T_1^{-1}$ of the $^{235}$U. We find that the temperature dependence of $T_1^{-1}$ for both $^{235}$U and $^{121}$Sb follows the power law ($\propto T^n$) with the small exponent $n=0.3$ suggesting that the same relaxation mechanism dominates the on-site and the ligand nuclei, but an anomaly at 5 K was observed, possibly due to the change in the transferred hyperfine coupling on the Sb site.