Conical antiferromagnetic order in the ferroelectric phase of Mn0.8Co0.2WO4

Abstract

Evolution of competing commensurate collinear (AF4) and incommensurate cycloidal (AF2) magnetic structures in Mn 0.8 Co 0.2 WO 4 multiferroic was studied by neutron diffraction, magnetic, and pyroelectric characterization measurements. In contrast to pure and slightly Co doped MnWO 4 , the antiferromagnetic AF4 collinear phase [k 1 = ( Ferroelectric polarization along b axis was revealed below T FE in the low temperature conical phase resulting from the superposition of the AF4 and AF2 spin structures. The arrangement of the spins after the two successive magnetic transitions are thoroughly described. In particular, we found that spins in the AF4 phase are aligned along the easy direction in the ac plane (∼142• with respect to the c * axis), while the cycloidal AF2 spin order is developed in the magnetically hard directions, perpendicular to the easy one, and consequently the T FE decreases compared to the pure MnWO 4 .

Magnetic-field-induced spontaneous polarization reversal in multiferroicMn0.85Co0.15WO4Poudel1, Liang2, Wang3 et al. 2014Phys. Rev. B152140View full textAdd to dashboardCite

“…While cooling in a positive poling electric field, the ferroelectric polarization is first established at T C1 = 10.2 K due to the formation of domains with the AF2/4 conical spin structure. With θ = 36 • and ϕ = 0 • [36,42], the net P b includes two contributions according to Eq. (3).…”

“…Besides the suppression of the AF1 phase by a small amount of Co (similar to Zn doping), two more sudden changes of the magnetic order in the multiferroic phase upon increasing Co content have been reported [36,[40][41][42]. At about 7.5% Co content, the spin helix in the AF2 phase suddenly rotates by 90 • into the a-c plane causing a flop of the ferroelectric polarization from the b to the a axis (AF5 phase).…”

Direct observation of noncollinear order of Co and Mn moments in multiferroicMn0.85Co0.15WOHerrero‐Martín1, Dobrynin2, Mazzoli3 et al. 2015Phys. Rev. BSelf Cite8150View full textAdd to dashboardCite

“…For x < 0.15 the longest (easy) axis of the elliptical helix remains in the ac plane, rotating from 56 • (x = 0) to θ = 134 • (as in CoWO 4 ) with increasing Co content. Last, for x 0.15 AF2' disappears and Mn 1-x Co x WO 4 samples are then dominated by the collinear order inherent to CoWO 4 , AF4 [14,15,20]. Interestingly, in this region the collinear AF4 order [k = (1/2, 0, 0)] first appears at T N .…”

“…Noncollinear magnetic order in these compounds is a consequence of magnetic frustration due to their geometry and the contest between distinct exchange intrachain and interchain coupling terms of Heisenberg type and uniaxial anisotropy [12]. Thanks to their simple structure and rich ferroelectric (FE) behavior emergent ideas and phenomena involved in the ME response of improper MFs can be revealed or tested [5][6][7][8][9][10][11][12][13][14][15][16]. Among all Mn 1-x M x WO 4 (M: transition-metal) isostructural compounds with magnetic and nonmagnetic substitutions, Co generates the most complex and rich phase diagrams [5][6][7][8][9][10][11][12][13][14][15][16][17][18], and its large magnetocrystalline anisotropy has been hold responsible for it.…”

“…Decreasing temperature, there is a ferroelectric transition at T C < T N due to the appearance of the incommensurate AF2 cycloidal order (with spins rotating perpendicularly to the ac plane), which coexists with the collinear AF4 order below T C . The juxtaposition for x > 0.15 of the collinear AF4 and incommensurate AF2 orders generates an AF conical structure [14] (with the collinear and cycloidal spin components being perpendicular). So, we will focus on Mn 0.85 Co 0.15 WO 4 , of particular interest because it is regarded as the composition presenting maximum frustration in the family [15,20].…”