NUCLEAR MAGNETIC RESONANCE AND RELAXATION OF P-31 IN PARAMAGNETIC STATE OF UP-US SOLID SOLUTIONS

Measurements by continuous wave and pulsed NMR were made on P31 in the paramagnetic state of the UP-US solid solutions. All the UP1-xSx compositions used have a NaCl-type structure, are good conductors of electricity, and show systematic changes in the paramagnetic Curie temperature θ 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 ΔH, the Bloch decay time constant T2*, the echo decay time constant T2, and the spin-lattice relaxation time T1 as functions of temperature T and sulfur concentration x. K is linear in the molar susceptibility, K=K0+(4.0±0.5)χM, with |K0|K, and with a slope independent of x and similar to the slopes of K versus χM for other U compounds with magnetic ordering. The changes in θ and in magnetic ordering along the UP1-xSx 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 ΔH and T2* are dominated by inhomogeneous magnetic fields. The spin-spin relaxation time T2′, deduced from T2, is due mainly to homogeneous internuclear dipolar interactions. T1 increases with temperature for all compositions, regardless of the magnetic ordering. T1T is empirically related to K differently in the antiferromagnetic compositions (T1TK2≅const) and in the ferromagnetic compositions (T1TK≅const). The T1 results are analyzed in terms of recently proposed models for nuclear relaxation due to indirect interactions with localized magnetic moments via the conduction electrons. © 1969 The American Physical Society.