Spin-orbit coupling inactivity of Co$^{2+}$ ion in geometrically frustrated magnet GeCo$_2$O$_4$

TL;DR

This study investigates the magnetic and structural properties of GeCo$_2$O$_4$, revealing unexpected magnetic reflections and discussing the spin and orbital states of Co$^{2+}$ ions, highlighting the inactivity of spin-orbit coupling.

Contribution

It provides new insights into the magnetic ordering and spin-orbit coupling behavior of Co$^{2+}$ in a geometrically frustrated magnet.

Findings

Discovery of magnetic Bragg reflections with a tetragonal propagation vector.

Observation of tetragonal lattice expansion below T_N.

Discussion of the spin and orbital states of Co$^{2+}$ ions.

Abstract

We report single-crystal neutron diffraction studies on a spinel antiferromagnet GeCo$_2$O$_4$, which exhibits magnetic order with a trigonal propagation vector and tetragonal lattice expansion ($c/a\simeq1.001$) below $T_{\rm N}=21$ K. For this inconsistency between spin and lattice in symmetry, magnetic Bragg reflections with a tetragonal propagation vector were discovered below $T_{\rm N}$. We discuss spin and orbital states of Co$^{2+}$ ion underlying the new magnetic component.