Dimensional reduction by geometrical frustration in a cubic antiferromagnet composed of tetrahedral clusters

TL;DR

This paper demonstrates how geometrical frustration in a cubic antiferromagnet induces emergent two-dimensional and one-dimensional spin behaviors, despite the three-dimensional crystal structure, revealing tunable low-dimensional properties.

Contribution

It shows that geometrical frustration can lead to emergent low-dimensional spin dynamics in a cubic antiferromagnet, supported by experimental and theoretical analysis.

Findings

Spin correlation exhibits two-dimensional characteristics.

Low-energy one-dimensional excitation modes are observed.

External magnetic fields can manipulate the emergent dimensionality.

Abstract

Dimensionality is a critical factor in determining the properties of solids and is an apparent built-in character of the crystal structure. However, it can be an emergent and tunable property in geometrically frustrated spin systems. Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet, pharmacosiderite, via muon spin resonance and neutron scattering. We find that the spin correlation exhibits a two-dimensional characteristic despite the isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in the three-dimensional cubic crystal, which we ascribe to two-dimensionalisation by geometrical frustration based on spin wave calculations. Moreover, we suggest that even one-dimensionalisation occurs in the decoupled layers, generating low-energy and one-dimensional excitation modes, causing large spin fluctuation in the classical spin system. Pharmacosiderite facilitates studying the emergence of low-dimensionality and manipulating anisotropic responses arising from the dimensionality using an external magnetic field.