Mechanism of ferromagnetic ordering of the Mn chains in CaMnGe${}_2$O${}_6$ clinopyroxene

Abstract

The electronic and magnetic properties of clinopyroxene CaMnGe${}_2$O${}_6$ were studied using density function calculations within the GGA+U approximation. It is shown that anomalous ferromagnetic ordering of neighboring chains is due to a "common-enemy" mechanism. Two antiferromagnetic exchange couplings between nearest neighbours within the Mn-Mn chain and interchain coupling via two GeO${}_4$ tetrahedra suppress antiferromagnetic exchange via single GeO${}_4$ tetrahedron and stabilize ferromagnetic ordering of Mn chains.

5 pages, 4 figures. Accepted to JETP Letters

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