Anomalous Magnetic Behavior in Ba2CoO4 with Isolated CoO4 Tetrahedra

TL;DR

This study reveals that Ba2CoO4 exhibits complex magnetic behaviors, including 3D antiferromagnetic order and quasi-2D spin dynamics, despite its isolated CoO4 tetrahedra, highlighting unique low-dimensional magnetic phenomena in oxides.

Contribution

The paper demonstrates the coexistence of 3D magnetic order with low-dimensional spin dynamics in Ba2CoO4, a system with isolated tetrahedra, revealing novel magnetic interactions.

Findings

Ba2CoO4 shows 3D noncollinear antiferromagnetic order.

The system exhibits quasi-2D spin wave dispersion.

There is a large spin gap and 1D magnetoelastic coupling.

Abstract

The dimensionality of the electronic and magnetic structure of a given material is generally predetermined by its crystal structure. Here, using elastic and inelastic neutron scattering combined with magnetization measurements, we find unusual magnetic behavior in three-dimensional (3D) Ba2CoO4. In spite of isolated CoO4 tetrahedra, the system exhibits a 3D noncollinear antiferromagnetic order in the ground state with an anomalously large Curie-Weiss temperature of 110 K compared to TN = 26 K. More unexpectedly, spin dynamics displays quasi-2D spin wave dispersion with an unusually large spin gap, and 1D magnetoelastic coupling. Our results indicate that Ba2CoO4 is a unique system for exploring the interplay between isolated polyhedra, low-dimensional magnetism, and novel spin states in oxides.