Spin structure and magnetic frustration in multiferroicRMn2O5(R=Tb

Abstract

We have studied the crystal and magnetic structures of the magnetoelectric materials RMn 2 O 5 ͑R =Tb,Ho,Dy͒ using neutron diffraction as a function of temperature. All three materials display incommensurate antiferromagnetic ordering below 40 K, becoming commensurate on further cooling. For R =Tb,Ho, a commensurate-incommensurate transition takes place at low temperatures. The commensurate magnetic structures have been solved and are discussed in terms of competing exchange interactions. The spin configuration within the ab plane is essentially the same for each system, and the radius of R determines the sign of the magnetic exchange between adjacent planes. The inherent magnetic frustration in these materials is lifted by a small lattice distortion, primarily involving shifts of the Mn 3+ cations and giving rise to a canted antiferroelectric phase.

Strong magnetoelastic coupling and unconventional electric polarization in the triangular-lattice multiferroic Li0.99Cu0.01CrODey1, Karmakar2, Majumdar3 et al. 2013Phys. Rev. B194181View full textAdd to dashboardCite

“…17 Recently, a similar evidence of uncompensated spontaneous electric polarization was reported in RMn 2 O 5 series where Jahn-Teller distortion led to the displacement of Mn 3+ ions giving rise to the uncommon canted AFE state. [27][28][29] Here, we display another unique case of uncompensated spontaneous electric polarization in a dissimilar system apart from the involvement of Jahn-Teller effect. Rather, a strong magnetoelastic coupling without orbital degeneracy in LCCO holds the key for the observed unconventional electric ordering.…”

“…17 The similar uncompensated P involving AFE ordering has been rarely reported in very few systems. [27][28][29] A kind of intricate canted AFE state has been proposed in RMn 2 O 5 . 27-29 Our observation also indicates a kind of AFE ordering below T AFE close to 61 K with a fairly large uncompensated electric polarization.…”

Magnetoelastic effects and the magnetic phase diagram of multiferroicDyMn2O5

“…1 The physical origin of this phase complexity lies in the partially competing interactions between the Mn 4+ /Mn 3+ spins, the rare earth magnetic moments, and the lattice. 2 Geometric magnetic frustration among the Mn 3+ −Mn 4+ spins leads to a ground state degeneracy of the magnetic states that can be lifted by a distortion of the lattice ͑magnetic Jahn-Teller effect͒. This is believed to be the origin of ferroelectricity in RMn 2 O 5 compounds.…”

“…This is believed to be the origin of ferroelectricity in RMn 2 O 5 compounds. [2][3][4] Strong spin-lattice coupling is needed to explain the ionic displacements in the FE state. The experimental proof of sizable lattice anomalies at the FE transitions in RMn 2 O 5 was given recently by thermal expansion experiments in zero magnetic field.…”

Collective phase-like mode and the role of lattice distortions atTN∼TCin RMn2O5(R= Pr, Sm, Gd, Tb, Bi)

“…The quenched Jahn-Teller orbital in the dimmer will locally unveil uncorrelated very weak new internal vibrational modes at low temperatures that will also correlate to the small shifts in Mn 3+ lattice position measured by neutron diffraction . [61]. The net weak lattice polarization (ferroelectricity) at ~T C would then be a natural consequence.…”