Cu nuclear quadrupole resonance and magnetic phase transition in CuO

Abstract

Cu-nuclear quadrupole resonance (NQR) frequency and relaxation rates measurements in CuO, in the vicinity of the antiferromagnetic ordering temperature TN, are presented. As T→T+N divergent behaviors of the relaxation rates T−11,2 and an anomalous decrease in the NQR frequency are observed. These effects are discussed in light of the temperature dependence expected for conventional one-dimensional Heisenberg paramagnet and some anomalies are interpreted as possible results of valence fluctuations in the CuO bond character.