Neutron diffraction, magnetic, and magnetoelectric studies of phase transitions in multiferroic Mn0.90Co0.10WO

Abstract

We have studied various spontaneous and magnetic-field-induced phase transitions in single crystals of multiferroic Mn 0.9 Co 0.1 WO 4 using magnetic and magnetoelectric measurements and neutron diffraction. Compared to pure MnWO 4 , our data consistently confirm that the anisotropic Co 2+ ions induce reorientation of the spin cycloid structure to the ac plane and reveal P a and P c components of spontaneous electric polarization. Field-induced phase transitions accompanied by anomalies of magnetic susceptibility and suppression of both P a and P c polarizations have been observed for H c (∼3 T) and H a (∼8.5 T). Neutron diffraction has revealed that in both cases the spin cycloid plane flops in direction almost perpendicular to H , i.e., close to the ab and bc planes, respectively. Parameters describing the magnetic structures including wave vectors, orientations of the main elliptical axes, etc., have been determined in all spontaneous and field-induced states.

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

“…The refinement of the 212 latter type of reflections allows us to conclude that the incommensurate part is an elliptical cycloid, the eccentricity of which is = 0.61 according to the definition given in Ref. 22. The main axes of the cycloid are along b axis and a direction in the ac plane that makes and angle ω = 55 (1) • with the c * axis (ω = α + 90 • ).…”

“…The evolution of the multiferroic phases and ferroelectric properties in Mn 1−x T x WO 4 , where Mn 2+ is substituted by T 2+ ions (T = Fe, Co, Mg, Zn), has been the subject of numerous studies. [13][14][15][16][17][18][19][20][21][22] In particular, for the Co substituted system at cobalt concentrations above ∼ 3% the commensurate AF1 phase is suppressed and the ferroelectric cycloidal phase AF2 with P b remains stable down to the lowest temperatures. With further increasing of cobalt concentration, at x = 0.1, the spin cycloidal plane flops to the ac plane accompanied by reorientation of the polarization to the same plane.…”

“…With further increasing of cobalt concentration, at x = 0.1, the spin cycloidal plane flops to the ac plane accompanied by reorientation of the polarization to the same plane. 15,18,22 At higher doping (x = 0.15) a new antiferromagnetic AF4 phase with wave vector k = ( 1 2 ,0,0), inherent to the pure CoWO 4 , arises below T N ≈ 15 K and competes with the cycloidal and collinear phases found in MnWO 4 . This results in a complicated scenario of phase transitions between different spin structures.…”

Pressure effects on magnetic ground states in cobalt-doped multiferroicMn1−xCoxWO4

“…Only a few percent of cobalt suppresses the AF1 magnetic structure and stabilizes the AF2 phase. Further doping above x = 0.075 changes the spin structure into another spiral configuration (AF5 phase) accompanied by polarization flipping into the ac plane [35,37]. When the Co concentration goes beyond x = 0.15, the polarization changes back to the b axis, and the magnetic structure forms a conical configuration with two modulation vectors of both AF2 spiral and AF4 collinear components [35,36].…”

“…Among chemical substitutions with either magnetic or nonmagnetic ions, the Co-doped system exhibits the most complex magnetic properties [32][33][34][35][36][37][38]. Only a few percent of cobalt suppresses the AF1 magnetic structure and stabilizes the AF2 phase.…”