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

TL;DR

This study uses density functional calculations to explain the unusual ferromagnetic ordering in CaMnGe$_2$O$_6$, revealing a 'common-enemy' mechanism involving specific exchange interactions.

Contribution

It uncovers the microscopic mechanism behind ferromagnetic ordering in CaMnGe$_2$O$_6$, highlighting the role of interchain and intrachain exchange couplings.

Findings

Ferromagnetic ordering is due to a 'common-enemy' mechanism.

Interchain coupling via GeO$_4$ tetrahedra stabilizes ferromagnetism.

Antiferromagnetic couplings are suppressed by specific exchange pathways.

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.