Chemical doping-induced flop of ferroelectric polarization in multiferroicMn0.9Co0.1WO4

Abstract

We studied the multiferroic properties of the incommensurate spiral phase of Mn 1−x Co x WO 4 using singlecrystal neutron-diffraction and ferroelectric measurements. Whereas the rotational plane of the spin spiral is parallel to the b axis for x Յ 0.05, it flops by 90°for x = 0.10. As a result, the direction of the ferroelectric polarization also flops from the b to the a axis. These results show that the orientation of the ferroelectric polarization in MnWO 4 can be controlled via chemical doping.

Neutron diffraction, magnetic, and magnetoelectric studies of phase transitions in multiferroic Mn0.90Co0.10WOUrcelay-Olabarría1, Ressouche2, Mukhin3 et al. 2012Phys. Rev. B237390View full textAdd to dashboardCite

“…The two characteristic temperatures are in a good agreement with the data reported in Ref. 17 and associated with appearance of the AF3 phase below T N and with the AF3-AF2 transition at T N2 . Though below T N the a-axis susceptibility decreases faster than the one along the c axis, they both change in a similar fashion and in disparity with the relatively small decrease in the b-axis susceptibility.…”

“…This component of the polarization (∼20 μC/m 2 ) was also observed in Ref. 17. In addition, the spin-wave excitation study on MnWO 4 13 confirmed that exchange coupling between chains along the a axis is as strong as that along the c axis and similarly strongly frustrated.…”

“…The observed 094436-2 anisotropy is rather different from the one reported in Ref. 17. However, this discrepancy and the magnitude of the measured anisotropy itself should be taken with some precautions until careful measurements on a crystal with similar dimensions are reported or until after proper corrections for sample shape and size are made.…”

“…At higher doping the AF2 phase is supposed to transform into the AF2 magnetic phase having the same propagation vector but with different orientation of the moments. A recent work by Song et al 17 on Mn 0.9 Co 0.1 WO 4 single crystals determined that in zero field the magnetic structure of the multiferroic phase consists of a helix that rotates in the ac plane and revealed that the electric polarization lies in the ac plane as well. The phase diagram of further doped compositions is rather complicated: new magnetic phases appear and coexist at the same time, 19 which is a demonstration of the complexity of the cobalt doping in this system.…”

“…In order to enlarge the temperature range where the multiferroic phase is stable, MnWO 4 has been doped with isovalent metal and nonmetal ions. [13][14][15][16][17][18][19][20] It turned out that doping with Co 2+ is particularly interesting since it strongly stabilizes the multiferroic phase at low temperatures. According to preliminary data on powder samples, 16 the incommensurate multiferroic AF2 phase is expected to substitute the commensurate AF1 ordering at low temperature for cobalt doping above 3%.…”