Ultrafine MnWO4 nanoparticles and their magnetic properties

Ultrafine nanoparticles of MnWO4, a compound showing low-temperature multiferroicity in the bulk, were synthesized by the polyol method. Studies using powder X-ray diffraction, scanning and transmission electron microscopy, dynamic light scattering, differential sedimentation and sorption techniques show the formation of a single-phase material, which is composed of MnWO4 nanoparticles with a prolate ellipsoidal shape(short axis of 4-5 nm, long axis of 11-12 nm) and an unprecedented high specific surface area of 166 m(2) g(-1). The as-prepared MnWO4 nanoparticles are readily crystalline after the liquid-phase synthesis. Temperature and field dependent magnetization measurements indicate antiferromagnetic behavior with a single magnetic phase transition near T-N approximate to 6 K. In contrast, three successive transitions below 14 K were reported for multiferroic bulk-MnWO4. Above T-N, the nanoparticles show Curie-Weiss-type paramagnetic behavior. Due to the large paramagnetic moment of Mn2+ (mu(eff) approximate to 6.2 mu(B)), the nanoparticles can be easily manipulated by a bar magnet at ambient temperature. (C) 2015 Elsevier Masson SAS. All rights reserved.