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

Abstract

Ceramic samples of MnW 1−x Mo x O 4 (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 Mn 2+ ions in the spin spiral multiferroic MnWO 4 . Samples were characterized by X-ray diffraction, optical spectroscopy, magnetization, and dielectric permittivity measurements. It was observed that the Neél temperature T N , the spin spiral ordering temperature T M2 , and the ferroelectric phase-transition temperature T FE2 of MnWO 4 increased upon the nonmagnetic substitution of Mo 6+ for W 6+ . Like pure MnWO 4 , 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 MnMoO 4 that is isostructural with MnWO 4 suggests that Mo substitution increases the strength of the spin-exchange couplings among Mn 2+ in the vicinity of a Mo 6+ ion. Our study shows that the Mo-doped MnW 1−x Mo x O 4 (x ≤ 0.3) compounds are spin-frustrated materials that have higher magnetic and ferroelectric phase-transition temperatures than does pure MnWO 4 .

Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution

“…With the introduction of non-magnetic Mo into MnWO 4 , the magnetic structure does not change but the transition temperature increases with Mo substitution. 6 There is also a detailed report on the transition metal doped FeVO 4 , in which the magnetic ordering does not change no matter it is magnetic doping nor nonmagnetic doping, and the ferroelectric ordering is even kept at a big doping rate. 42 The nonmagnetic doping on frustrated Ni 3 V 2 O 8 only plays a dilution effect on the magnetic structure.…”

“…[1][2][3][4][5][6][7] In such kinds of frustrated magnetic systems, many unique magnetic structures and physical properties are observed. [8][9][10][11][12] Magnetic monopoles have even been proposed to exist in some frustrated spin ice systems (for example, Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 ).…”

Suppression of the commensurate magnetic phase in nanosized hübnerite MnWO4

“…An attempt to increase local strain and promote anisotropy disorder was made by substituting tungsten with nominally 15 % molybdenum. The addition of Mo in the bulk form has been investigated earlier by Meddar et al [22] and has been shown to slightly raise the transition temperatures.…”

“…However, MnWO 4 still has technological potential at ambient temperatures, for example in humidity sensors and efforts have been made to increase the active surface by varying crystallite size [18,19], changing morphology [20], or doping [21,22].…”

“…5 and there are no signs of commensurate order down to 2.5 K. The area of the peaks extracted from the experimental data clearly revealed a notable discontinuity in intensity between 8.0 K and 8.5 K, which indicated the possible presence of another transition, which is verified by comparison with thermal neutron data taken at 9 K. The order parameter was fit in a temperature range 8. The values of parameters extracted from the fits were: for peak M1 T N =12.11(3) K, 2β=0.53 (22) and for peak M2 T N =12.12(3) K, 2β=0.41 (17). The values in parentheses represent statistical uncertainty on a 1-σ level, so 12.12(3) is equivalent to 12.12 ± 0.03.…”