Uncovering the magnetic structures of geometrically frustrated layered iron oxofluorophosphates

KFe(PO3F)2 and (NH4)2Fe(PO3F)2Cl are two new representatives of the layered iron oxofluorophosphate family AFe(PO3F)2 (A = K, NH4, (NH4)2Cl). Their crystal structures comprise different cationic buffers between Fe(PO3F)2 layers in which Fe atoms form equilateral triangular sublattices. Magnetization measurements indicate antiferromagnetic interactions and supressed magnetic order. The latter arises from the combination of low dimensionality and the geometrically frustrated Fe sublattice. Despite significantly different interlayer distances, both compounds order at comparable temperatures around 3 K suggesting possible unconventional exchange interactions. Since complex incommensurate magnetic structures are expected as their ground states, neutron powder diffraction using the high-resolution cold neutron diffractometer WISH will help to uncover their magnetic structures.