Nuclear Magnetic Resonance and Relaxation ofP31in the Paramagnetic State of the UP-US Solid Solutions

Measurements by continuous wave and pulsed NMR were made on ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ in the paramagnetic state of the UP-US solid solutions. All the $\mathrm{U}{\mathrm{P}}_{1-x}{\mathrm{S}}_x$ compositions used have a NaCl-type structure, are good conductors of electricity, and show systematic changes in the paramagnetic Curie temperature $\theta$ and in the magnetic ordering, from type-I antiferromagnetic in UP to ferromagnetic in the US-rich compositions. Measurements were made of the Knight shift $K$, the linewidth $\Delta H$, the Bloch decay time constant ${T_2}^{*}$, the echo decay time constant $T_2$, and the spin-lattice relaxation time $T_1$ as functions of temperature $T$ and sulfur concentration $x$. $K$ is linear in the molar susceptibility, $K=K_0+(4.0\mathrm{}\pm 0.5){\chi }_M$, with $\left|K_0\right|\ll K$, and with a slope independent of $x$ and similar to the slopes of $K$ versus ${\chi }_M$ for other U compounds with magnetic ordering. The changes in $\theta$ and in magnetic ordering along the $\mathrm{U}{\mathrm{P}}_{1-x}{\mathrm{S}}_x$ system that could be accounted for by RKKY-type (Rudermann-Kittel-Kasuya-Yosida) interactions are not reflected in $K$, thereby disqualifying the RKKY model for the Knight shift. The broad NMR lines are due to inhomogeneous effects in the powder samples (demagnetization and composition variation), and both $\Delta H$ and ${T_2}^{*}$ are dominated by inhomogeneous magnetic fields. The spin-spin relaxation time ${T_2}^{\prime }$, deduced from $T_2$, is due mainly to homogeneous internuclear dipolar interactions. $T_1$ increases with temperature for all compositions, regardless of the magnetic ordering. $T_{1}T$ is empirically related to $K$ differently in the antiferromagnetic compositions ($T_{1}T{K}^2\cong \mathrm{const}$) and in the ferromagnetic compositions ($T_1\mathrm{TK}\cong \mathrm{const}$). The