Partial frustration of magnetic order in synthetic angelellite, Fe4As2O11

Abstract

The antiferromagnetic structure of Fe₄As₂O₁₁ has been solved from neutron powder diffraction data below the Neel temperature of 159 K. A 2a × b × c magnetic supercell is adopted and the two crystallographically distinct Fe³⁺ sites order with different critical exponents and with saturated magnetic moments of 3.34(2) and 4.37(2) μ_B. The large difference between these magnetic moments reflects differing degrees of frustration at the two sites. Structural refinement using high resolution powder neutron diffraction data confirms the structural model previously reported and no evidence for the presence of an OH group associated with a very short Fe–O distance of 1.76(2) Å is found.