User talk:Jstein: Difference between revisions
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Revision as of 13:34, 2 February 2012
Multiferroic building site
New topics
definition
insert headline here
critical temperature
list of materials
| crystal | Tc [K] | Type |
|---|---|---|
| TbMnO3 | 7 and 27 | spiral spin |
| MnWO4 | 13.5[1] | spiral spin |
electron-electron exchange
OLD PAGE FOLLOWS
Magnetically driven ferroelectricity
Magnetically driven multiferroics are insulating materials, mostly oxides, in which macroscopic electric polarization is induced by magnetic long-range order. A necessary but not sufficient condition for the appearance of spontaneous electric polarization is the absence of inversion symmetry. In these materials inversion symmetry is broken by magnetic ordering. Such a symmetry breaking often occurs in so-called frustrated magnets, where competing interactions between spins favor unconventional magnetic orders. The microscopic mechanisms of magnetically induced ferroelectricity involve the polarization of electronic orbitals and relative displacement of ions in response to magnetic ordering.
Many multiferroics show the cycloidal spiral ordering, in which spins rotate around an axis perpendicular to the propagation vector of the spiral. The induced electric polarization is orthogonal to the propagation vector and lies in the spiral plane. An abrupt change of the spiral plane induced by magnetic field results in the corresponding rotation of the polarization vector. In DyMnO3 this transition is accompanied by the 600% increase of dielectric constant (the giant magnetocapacitance effect[2]). The microscopic mechanism of magnetoelectric coupling in spiral multiferroics involves spin-orbit coupling.
E-type Antiferromagnet (I.e. ortho-HoMnO3): In the presence of strong uniaxial anisotropy, as in the ANNNI model,[3] competing interaction can stabilize a *periodic collinear spin arrangement of the up-up-down-down* type. Such a spin modulation commensurate with the structural or charge modulation can induce electric polarization via exchange striction mechanism that does not require spin-orbit coupling.
- ^ "Effect of magnetic field and temperature on the ferroelectric loop in MnWO4".
{{cite journal}}: Cite journal requires|journal=(help) - ^ T. Goto et al., Phys. Rev. Lett. 92, 257201 (2004)
- ^ M.E.Fisher and W.Selke, Phys.Rev. Lett. 44,1502 (1980)