³¹P NMR Studies of the Magnetically Ordered Heavy-Electron Compound YbP

The microscopic magnetic properties of the heavy-electron compound YbP have been investigated by ³¹P NMR at temperatures from 0.38 to 600 K. The observations of both an abrupt decrease of 1 / T₁ at around 0.7 K and additional broadening of the spectrum below this temperature show that YbP orders magnetically at low temperatures. In the paramagnetic state, the Knight shift vs susceptibility plot exhibits a marked change of the slope at around 100 K with a larger hyperfine coupling constant of –4.02 kOe/μ_B below 100 K. Based on a semimetallic band structure of the compound, a simple model is presented, in which the previously observed anomalous broad maximum in the low-temperature specific heat is ascribed to the Kondo effect due to a large mixing between a Γ₆ ground state of 4f hole of Yb³⁺ ion and occupied P-derived 3p states in the valence bands. The contribution of this p-f mixing mechanism to the transferred hyperfine interaction is also evaluated.