Suppression of the commensurate magnetic phase in nanosized hübnerite MnWO4

Abstract

Magnetic structures of nanosized (20 nm to 70 nm) powders of MnWO 4 and MnWO 4 :Mo were studied using neutron powder diffraction (NPD). Sizes and shapes of the crystallites calculated from anisotropic peak broadening of diffraction peaks were found to be orthogonal parallelepiped-like with the longest edge along the c-axis and the shortest along the b-axis. SQUID measurements indicate the presence of two magnetic transitions around 8 K and 12 K. Rietveld refinement of the NPD data below the magnetic transition was consistent with the presence of an incommensurate spiral like (ac-AF2) phase. A commensurate phase AF1 was not observed down to 2.5K for all of the samples.