Increasing the Phase-Transition Temperatures in Spin-Frustrated Multiferroic MnWO4 by Mo Doping

• Published in: Chemistry of materials 2012-01, Vol.24 (2), p.353-360
• Main Authors: Meddar, Lynda, Josse, Michaël, Maglione, Mario, Guiet, Amandine, La, Carole, Deniard, Philippe, Decourt, Rodolphe, Lee, Changhoon, Tian, Chuan, Jobic, Stéphane, Whangbo, Myung-Hwan, Payen, Christophe
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Material chemistry
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm2031653

Ceramic samples of MnW1–x Mo x O4 (x ≤ 0.3) solid solution were prepared by a solid-state route with the goal of increasing the magnitude of the spin-exchange couplings among the Mn2+ ions in the spin spiral multiferroic MnWO4. Samples were characterized by X-ray diffraction, optical spectroscopy, magnetization, and dielectric permittivity measurements. It was observed that the Néel temperature T N, the spin spiral ordering temperature T M2, and the ferroelectric phase-transition temperature T FE2 of MnWO4 increased upon the nonmagnetic substitution of Mo6+ for W6+. Like pure MnWO4, the ferroelectric critical temperature T FE2(x) coincides with the magnetic ordering temperature T M2(x). A density functional analysis of the spin-exchange interactions for a hypothetical MnMoO4 that is isostructural with MnWO4 suggests that Mo substitution increases the strength of the spin-exchange couplings among Mn2+ in the vicinity of a Mo6+ ion. Our study shows that the Mo-doped MnW1–x Mo x O4 (x ≤ 0.3) compounds are spin-frustrated materials that have higher magnetic and ferroelectric phase-transition temperatures than does pure MnWO4.