Ultrafine MnWO4 nanoparticles and their magnetic properties

• Polyol synthesis of magnetic MnWO4 nanoparticles.
• Prolate ellipsoidal particle shape and an unprecedented high specific surface area of 166 m2 g−1.
• Readily crystalline nanoparticles with 10 nm in size after liquid-phase synthesis.
• Nanoparticles can be manipulated with bar magnet (room temperature) and a single magnetic phase transition (6 K).

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 m2 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 TN ≈ 6 K. In contrast, three successive transitions below 14 K were reported for multiferroic bulk-MnWO4. Above TN, the nanoparticles show Curie–Weiss-type paramagnetic behavior. Due to the large paramagnetic moment of Mn2+ (μeff ≈ 6.2 μB), the nanoparticles can be easily manipulated by a bar magnet at ambient temperature.

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