Abstract
Results of magnetic eld and temperature dependent neutron di raction and magnetization mea-
surements on oxy-arsenate Rb2Fe2O(AsO4)2 are reported. The crystal structure of this compound
contains pseudo-one-dimensional [Fe2O6] sawtooth-like chains, formed by corner sharing isosce-
les triangles of Fe3+ ions occupying two nonequivalent crystallographic sites. The chains extend
in nitely along the crystallographic b-axis and are structurally con ned from one another via dia-
magnetic (AsO4)3- units along the a-axis, and Rb+ cations along the c-axis direction. Neutron
di raction measurements indicate the onset of a long range antiferromagnetic order below approxi-
mately 25 K. The magnetic structure consists of ferrimagnetic chains which are antiferromagnetically
coupled with each other. Within each chain, one of the two Fe sites carries a moment which lies
along the b-axis, while the second site bears a canted moment in the opposite direction. Exter-
nally applied magnetic eld induces a transition to a ferrimagnetic state, in which the coupling
between the sawtooth chains becomes ferromagnetic. Magnetization measurements performed on
optically-aligned single crystals reveal evidence for an uncompensated magnetization at low mag-
netic elds that could emerge from to a phase-segregated state with ferrimagnetic inclusions or from
antiferromagnetic domain walls. The observed magnetic states and the competition between them
is expected to arise from strongly frustrated interactions within the sawtooth chains and relatively
weak coupling between them.
