We show that pharmacosiderite is a novel cluster antiferromagnet comprising frustrated regular tetrahedra consisting of spin-5=2 Fe3+ ions arranged in the primitive cubic lattice. The connectivity of the tetrahedra and inter-cluster interaction of 2.9 K, which is significantly large compared with the intra-cluster interaction of 10.6 K, provide a unique platform for frustration physics. An unconventional antiferromagnetic order is observed below TN ~ 6 K, accompanied by a weak ferromagnetic moment and large fluctuation, as demonstrated by Mössbauer spectroscopy. A q = 0 magnetic order with a total S = 0 for the tetrahedral cluster is proposed based on an irreducible representation analysis, which may explain the origin of the weak ferromagnetism and fluctuation.
ASJC Scopus subject areas
- Physics and Astronomy(all)