Understanding the unusual magnetic susceptibility anisotropies of La₂CuO₄

Marcello Barbosa da Silva Neto

Institute for Theoretical Physics, University of Utrecht

The magnetic and thermodynamic properties of La2CuO4 are studied within a long wavelength effective theory for the quantum Heisenberg antiferromagnet that incorporates both the Dzyaloshinskii-Moriya and pseudo-dipolar anisotropy terms. We provide a simple and clear explanation for all the recently reported unusual magnetic anisotropies in the low-field susceptibility of La2CuO4, L. N. Lavrov et al., Phys. Rev. Lett. 87, 017007 (2001), and we demonstrate explicitly why La2CuO4 can not be classified as an ordinary easy-axis antiferromagnet.