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

Abstract

Using ambient pressure x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn1−xCoxWO4 single crystals (x = 0, 0.05, 0.135 and 0.17), and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the c direction. At high doping level (x = 0.135 and 0.17), pressure and Co doping drive the system in a similar way and induce a spin-flop transition for the x = 0.135 compound. In contrast, magnetic ground states at lower doping level (x = 0 and 0.05) are robust against pressure but experience a pronounced change upon Co substitution. As Co introduces both chemical pressure and magnetic anisotropy into the frustrated magnetic system, our results suggest the magnetic anisotropy is the main driving force for the Co induced phase transitions at low doping level, and chemical pressure plays a more significant role at higher Co concentrations.PACS numbers: 75.30. Kz,75.85.+t There has been long pursuit for materials showing coupled magnetic and electric properties, for both technological potential and fundamental scientific interest. Inspired by the magnetic control of ferroelectric polarization in TbMnO 3 [1], considerable interest has focused on the "type II" multiferroic materials where the ferroelectricity has a magnetic origin [2][3][4][5][6]. It can be realized through spin current or inverse Dzyaloshinskii-Moriya interaction [7][8][9], exchange striction [10], and p-d hybridization mechanism [11,12]. Magnetic frustration is a key ingredient in these materials where the competing interactions often lead to noncollinear spin structure and delicately balanced ground states, and the corresponding electric or magnetic properties can be easily tuned by external perturbations.The multiferroic MnWO 4 is a classic example of frustrated magnets with coupled electric and magnetic properties [13][14][15]. It crystallizes in the monoclinic wolframite structure (space group P 2/c). The edge-sharing MnO 6 octahedra form zigzag chains along the c axis [ Fig. 1 (a)]. When cooling, MnWO 4 undergoes successive magnetic transitions [16]. The incommensurate (ICM) AF3 phase orders below 13.5 K, forming a collinear sinusoidal structure with a T -dependent magnetic wavevector. An ICM AF2 phase is stabilized between 7 K < T < 12.6 K, with the wavevector locked at q = (0.214, 0.5, −0.457), hosting a spiral magnetic structure that breaks the inversion symmetry [17] and a spontaneous electric polarization along the b axis. Below 7 K, the electric polarization disappears simultaneously with the AF2 phase. The commensurate AF1 phase sets in with wavevector q = (0.25, 0.5, −0.5), forming a collinear ↑↑↓↓ configuration along the chain.Both experimental [18,19] and theoretical [20,21] studies have revealed sizable long-range magnetic interactions. The system is susceptible to different perturbations including magnetic field [13,[22][23][24][25] and chemical doping [26][27][28][29][30][31].Among chemical substitutions with either...

A Brief Review of the Effects of Pressure on Wolframite-Type Oxides

“…Those works have found that pressure is able to disrupt the fine equilibrium of the frustrated antiferromagnetic phase of MnWO 4 (AF1) but enhance the Néel temperature of the AF3 and AF4 magnetic phases of pure or lowly Co-doped MnWO 4 and highly Co-doped MnWO 4 , respectively. Considering the direct effect that pressure has on the spin structure that is even able to cause a spin-flop transition for highly Co-doped MnWO 4 [59], one can expect a new and fascinating phase diagram in the HP phase of MnWO 4 , where distortions are expected to be higher due to the lowering of symmetry from space group P2/c to P1. So far, the only study done in this direction has been done with CuWO 4 ; according to calculations in that study, the structural phase transition from P2/c to P1 also involves an antiferromagnetic to ferromagnetic order [60].…”

“…In recent years, some works have appeared to deal with the pressure-temperature magnetic phase diagram of pure [9,58] or cobalt alloyed [59] MnWO 4 . Those works have found that pressure is able to disrupt the fine equilibrium of the frustrated antiferromagnetic phase of MnWO 4 (AF1) but enhance the Néel temperature of the AF3 and AF4 magnetic phases of pure or lowly Co-doped MnWO 4 and highly Co-doped MnWO 4 , respectively.…”

Two spin-canting textures in the antiferromagnetic phase AF1 of MnWO4based on the new polar atomistic model inP2

“…The desired spin-orbitlattice coupling can be enhanced by introducing chemical pressures and magnetic anisotropy into the frus trated zigzag chains of the spin system in MnWO 4 . This can be further controlled by applying external electric and magn etic fields [6,34,35] or under pressure [36]. For instance, according to [37], in Mn 1−x Co x WO 4 the chiral spin order is preserved at domain boundaries between two chemical zones around x = 0.15 (helical AF5 and conical AF2/AF4 domains).…”

Brief Review of the Effects of Pressure on Wolframite-Type Oxides

“…In recent years some works have appeared dealing with the pressure-temperature magnetic phase diagram of pure [58] or cobalt alloyed [59] MnWO4. Those works have found that pressure is able to disrupt the fine equilibrium of the frustrated antiferromagnetic phase of MnWO4 (AF1) but enhance the Néel temperature of the AF3 and AF4 magnetic phases of pure or lowly Co-doped MnWO4 and highly Co-doped MnWO4, respectively.…”