MAGNETIC-STRUCTURES OF MNPO4.D2O AND MNASO4.D2O FROM TIME-OF-FLIGHT NEUTRON POWDER DIFFRACTION DATA

The magnetic properties of the isomorphous compounds MnXO4.D2O (X = P, As) have been investigated by magnetic-susceptibilitY and low-temperature time-of-flight neutron powder diffraction methods. These materials behave as Curie-Weiss paramagnets at high temperatures and order antiferromagnetically below Neel temperatures of 33 and 24 K for X = P and As, respectively. The 4 K magnetic structures of the two compounds have been determined from time-of-flight neutron powder diffraction and consist of antiferromagnetic Mn-O-Mn chains in the [101] direction with ordered magnetic moments of 3.52(5) and 3.54(5)mu(B), for X=P and As, parallel to [101]. The crystal structures have also been refined precisely from the same data, and the resulting bond distances and angles are used to rationalise the relative strengths of the interchain magnetic superexchange interactions.