Temperature dependence of the sublattice magnetization in the quasi-two-dimensionalS=1/2Heisenberg antiferromagnetLa2CuO4

We report the measurement of the Cu nuclear magnetic resonance (NMR) spectra up to high temperatures (160 K) in the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet ${\mathrm{La}}_2{\mathrm{CuO}}_4$ ${(T}_N$=312 K). The normalized NMR frequency, which is directly proportional to the decrease of the sublattice magnetization, follows the power law ${\mathrm{AT}}^{\alpha }$ with $A$=(6.9±0.5)$\times {10}^{-6}$ and α=(2.00±0.01) below about 100 K, while it is slightly suppressed above 100 K. The sublattice magnetization has been calculated numerically using a linear-spin-wave model. Good agreement with the experimental data is obtained by using the following coupling constants which were reported previously: The intraplane exchange coupling $J=1590\mathrm{}$ K, the intraplane $x$-$y$ symmetric exchange coupling $J_{\mathrm{xy}}/J=1.5\mathrm{}\times {10}^{-4}$, and the interplane exchange coupling $J^{\prime }/J=5\mathrm{}\times {10}^{-5}.$ In addition, we have determined the quadrupole frequency, the angle between the internal magnetic field, and the axis of the maximum component of the electric field gradient tensor, and this tensor’s asymmetry parameter.