NQR study of copper in Lu_0.9Pr_0.1Ba₂Cu₃O₇

Abstract

Nuclear quadrupole resonance (NQR) of copper in Lu_0.9Pr_0.1Ba₂Cu₃O₇ at 4.2 K has been observed. The resonances of ⁶³Cu(II) and ⁶⁵Cu(II) have been observed at 31.50 and 29.15 MHz, respectively. These frequencies are the same as those in YBa₂Cu₃O₇ but not in accordance with the expectations from the decrease of resonance frequency in RBa₂Cu₃O₇ compounds. V_Q⁶³/ν_Q⁶⁵ is 1.08 which is the ratio of the eQ(⁶³Cu)/eQ(⁶⁵Cu), implying that there is no static magnetic field at the Cu(II) site. The relaxation times T₁ and T₂ at 31.50 MHz have been determined and are found to be 42 ms and 140 μs, respectively. T₁ is much less than that (~1 s) in YBa₂Cu₃O₇ and EuBa₂Cu₃O₇, indicating that fluctuating moments are present in the material. These could be either on Cu ions that are close to Pr ions or on Pr ions themselves. The contrasting behavior of resonance frequency and T₁ in Lu_0.9Pr_0.1Ba₂Cu₃O₇ with respect to other 1:2:3 compounds is commented upon.