Molecular spin-orbit excitations in the J_eff = 1/2 frustrated spinel GeCo$_2$O$_4$

TL;DR

This study investigates magnetic excitations in GeCo$_2$O$_4$, revealing non-dispersive short-range excitations and a hidden molecular-singlet ground state, influenced by frustration and J_eff = 1/2 effects.

Contribution

It uncovers molecular excitations and a hidden ground state in a frustrated spinel, advancing understanding of quantum phenomena in J_eff = 1/2 systems.

Findings

Discovery of non-dispersive short-range magnetic excitations

Evidence for a hidden molecular-singlet ground state

Identification of precursor quasielastic excitations above T_N

Abstract

We describe powder and single-crystal inelastic neutron scattering experiments on a spinel-type antiferromagnet GeCo$_2$O$_4$, represented by an effective total angular momentum J_eff = 1/2. Several types of non-dispersive short-range magnetic excitations were discovered. The scattering intensity maps in $\vec{Q}$ space are well reproduced by dynamical structure factor analyses using molecular model Hamiltonians. The results of analyses strongly suggest that the molecular excitations below T_N arise from a hidden molecular-singlet ground state, in which ferromagnetic subunits are antiferromagnetically coupled. The quasielastic excitations above T_N are interpreted as its precursor. A combination of frustration and J_eff = 1/2 might induce these quantum phenomena.