7Li nuclear magnetic resonance spectra and relaxation in Ni1−xLixO

Abstract

7Li nuclear magnetic resonance (NMR) spectra and relaxation rates in Ni1−xLixO, for 0.01≤x≤0.46 and for 20≤T≤550 K are presented. For x≤0.2 the antiferromagnetic (AF) phase typical of NiO is still observed. The Neel temperatures TN(x), the temperature dependence of the field at the Li site, and the role of the extra holes in driving the correlated spin dynamics of Ni2+ are derived. In particular, from 7Li relaxation rates W the hopping frequencies of the holes on the AF background and the energy gaps between itinerant and localized states are extracted. In the mixed regime (x≥0.3, LiNiO2 structure-type) in which partial ordering on alternate Li+ and Ni3+ layers occurs, 7Li NMR data display the features typical of disordered paramagnets, consistent with a picture of random distribution of Ni3+ (S=1/2), Ni2+ (S=1) and of spin vacancies Li+ (S=0). In particular, for x=0.46, on cooling, a paramagnetic-like divergence of the width and of the shift of the NMR line is observed while 7Li W’s indicate slowing down of the spin fluctuations. The fluctuation frequency decreases in the MHz range below a freezing temperature Tf≂40 K.