Temperature Dependence of the Sublattice Magnetization Measured by Cu NMR in Quasi-Two-Dimensional Antiferromagnet YBa₂Cu₃O_6.1

Abstract

The Cu-NMR spectrum for Cu(2) site was measured from 1.5 K to 200 K in the quasi-two dimensional (2D) bilayer antiferromagnet, YBa₂Cu₃O_6.1. The nuclear Zeeman and quadrupole frequencies, ν_L and ν_Q were deduced from the spectrum. The decrease of the sublattice magnetization with increasing temperature was evaluated from the values ν_L as (ν_L(0)−ν_L(T))⁄ν_L(0) assuming no temperature dependence of the hyperfine coupling constant. The evaluated sublattice magnetization shows the almost linear temperature dependence at least above 25 K in log ((ν_L(0)−ν_L(T))⁄ν_L(0)) vs. log T plot. This temperature dependence of the sublattice magnetization is well explained quantitatively within a factor of two by the spin wave model in the quasi-2D antiferromagnet using the exchange coupling parameters reported previously by neutron scattering experiments.