UCL Discovery

Abstract

The magnetic structures of the perovskites NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6, with rocksalt ordering of the Mn/W ions and layered ordering of Na and the rare-earth ions, have been determined by neutron powder diffraction. The manganese moments in NaLaMnWO6 order below 10 K with a propagation vector of k(14)=(1/2,0,1/2) and a moment of 3.99 mu(B) per Mn2+ ion. The Mn2+ and Nd3+ ions order simultaneously in NaNdMnWO6 at 11 K. The resulting magnetic structure is incommensurate with the underlying crystal structure and has the propagation vector of k(5)= (0,0.48,1/2). NaTbMnWO6 undergoes two magnetic phase transitions at 15 and 9 K. The structure determined at 11 K is based on two propagation vectors of k(14) =(1/2,0,1/2) and k(5)= (0,0.427,1/2). Upon cooling at 6 K the incommensurate vector is no longer present and the moments order only according to k14. The moments of the Nd and Tb ions are found to remain within the planes of the A-site cations, and in NaTbMnWO6 the Mn moments also lie within the xy plane. This study not only reveals magnetic structures with previously unexplored topologies but it also sheds light on the intricate coupling between the two magnetic sublattices.