Interlayer Dzyaloshinskii-Moriya Interactions in a Quasi-Two-Dimensional Spin 1/2 Antiferromagnet Cu(en)(H2O)2SO4

We present a theoretical study of magnetic interlayer exchange couplings in a quasi-two-dimensional quantum antiferromagnet Cu(en)(H2O)(2)SO4 (en = C2H8N2). We use symmetry arguments to construct the most general form of interlayer spin exchange interactions, and discuss the significance of individual terms. Particular attention is paid to the antisymmetric Dzyaloshinskii-Moriya spin anisotropy, allowed for the interlayer interactions in the ab-planes. We argue that it should not lead to weak ferromagnetism of neither conventional nor hidden type. Instead, the distribution of Dzyaloshinskii-Moriya vectors is typical for helimagnets. However, the occurrence of helimagnetism appears unlikely due to the assumed hierarchy of the magnitudes of spin interactions and the opposite chirality in adjacent ab-planes.