Frustrated minority spins in GeNi2O4

TL;DR

This study reveals that in GeNi2O4, two magnetic phase transitions are driven by frustrated minority spins, with neutron scattering showing the ordering of kagome and triangular plane spins at different temperatures.

Contribution

The paper identifies the role of frustrated minority spins in GeNi2O4's two magnetic phase transitions and provides a magnetic exchange interaction scenario explaining their origin.

Findings

Two magnetic phase transitions at 12.1 K and 11.4 K.

Ordered kagome plane spins at T_N1, frustrated triangular spins.

Triangular spins order at T_N2.

Abstract

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi$_2$O$_4$ at $T_{N1}=12.1$ K and $T_{N2}=11.4$ K, respectively \cite{matsuno, crawford}. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at $T_{N1}$ the spins on the $<111>$ \kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the $<111>$ triangular planes that separate the \kagome planes frustrated and disordered. At the lower $T_{N2}$, the triangular spins also order in the $<111>$ plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.