Suppression of the commensurate magnetic phase in nanosized hübnerite MnWO4...

Magnetic structures of nanosized (20 to 70 nm) powders of MnWO4 and MnWO4: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 parallelepipedlike 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 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 2.5 K for all of the samples.