Low-Energy Magnetic Excitations in the Antiferromagnetically Ordered State of an Incipient Heavy-Electron Compound UP as Studied by31P NMR

Abstract

The microscopic magnetic properties of UP with the cubic NaCl-type structure have been investigated by 31 P NMR in the magnetically ordered state. 1/ T 1 is extraordinarily large in the single- Q type-I phase (\(T_{0}\cong 22.5\) K\(<t<t_{\rm N}\cong 122\) K), and shows about two orders of magnitude abrupt decrease through the single- Q ↔double- Q phase transition at T 0 . Below about 4 K in the double- Q type-I phase ( T < T 0 ), 1/ T 1 shows a Korringa-like temperature-dependence, which corresponds qualitatively to a 5 f -derived γ T term in the specific heat. We discuss this behavior as a clear indication of the existence of 5 f -derived very-low-energy magnetic excitations even in the ordered state, and an incipient heavy-electron character of the compound is concluded. We also present a simple qualitative model of a system of exchange-coupled Kondo impurities under internal exchange (or molecular) field in order to discuss the origin of these excitations.