ChemInform Abstract: Simultaneous Antiferromagnetic Order and Spin-Glass-Like Behavior in MnAsO4.

A low-temperature time-of-flight neutron powder diffraction study of a simple new solid, MnAsO4, in a sample also containing 20% Mn2As2O7 has been performed. MnAsO4 orders magnetically at 14.5(5) K, and the unusual antiferromagnetic structure below this temperature has been determined. Only half of the Mn3+ spins are ordered, and the remaining "idle" spins show some spin-glass behavior evidenced by susceptibility measurements. The ordered moment is reduced to a value of 2.6 mu(B) by frustration. It is not possible to determine which of the two crystallographically inequivalent Mn sublattices is magnetically ordered and which is idle. The antiferromagnetic structure of the minority phase Mn2As2O7 which orders at 10.5(5) K has also been determined.