Frustrated Magnetism of Pharmacosiderite Comprising Tetrahedral Clusters Arranged in the Primitive Cubic Lattice

TL;DR

This study reveals pharmacosiderite as a novel frustrated cluster antiferromagnet with tetrahedral Fe3+ ions arranged in a cubic lattice, exhibiting unconventional magnetic order and fluctuations due to inter-cluster interactions.

Contribution

It introduces pharmacosiderite as a new frustrated cluster antiferromagnet with unique magnetic properties and provides a detailed analysis of its magnetic order and fluctuations.

Findings

Unconventional antiferromagnetic order below 6 K

Presence of weak ferromagnetism and large fluctuations

Inter-cluster interaction significantly influences magnetic behavior

Abstract

We show that pharmacosiderite is a novel cluster antiferromagnet comprising frustrated regular tetrahedra made of spin-5/2 Fe3+ ions that are arranged in the primitive cubic lattice. The connectivity of the tetrahedra and the inter-cluster interaction of 2.9 K, which is significantly large compared with the intra-cluster interaction of 10.6 K, gives a unique playground for frustration physics. An unconventional antiferromagnetic order is observed below TN ~ 6 K, which is accompanied by a weak ferromagnetic moment and a large fluctuation as evidenced by Mossbauer spectroscopy. A q = 0 magnetic order with the total S = 0 for the tetrahedral cluster is proposed based on the irreducible representation analysis, which may explain the origin of the weak ferromagnetism and fluctuation.