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15 Apr 2006

Volume 99, Issue 8, Articles (08xxxx)

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back to top Symposium on Magnetic and Ferroelectronic Properties in Rare-Earth Oxides

Neutron-scattering studies of magnetism in multiferroic HoMnO3 (invited)

O. P. Vajk, M. Kenzelmann, J. W. Lynn, S. B. Kim, and S.-W. Cheong

J. Appl. Phys. 99, 08E301 (2006); http://dx.doi.org/10.1063/1.2162090 (6 pages) | Cited 10 times

Online Publication Date: 18 April 2006

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Hexagonal HoMnO3 is a frustrated antiferromagnet (TN = 72 K) ferroelectric (TC = 875 K) with a rich magnetic phase diagram consisting of multiple temperature- and field-dependent phases. Previously observed anomalies in the dielectric constant at magnetic phase transitions indicate strong coupling between the ferroelectricity and magnetism. Neutron-diffraction measurements in a magnetic field reveal new intermediate-field phases at low temperatures. Inelastic neutron-scattering measurements are used to establish the primary magnetic interactions and demonstrate that the spin dynamics in HoMnO3 are well described by a simple two-dimensional nearest-neighbor Heisenberg antiferromagnetic exchange J = 2.44 meV and a temperature-dependent anisotropy D.
Show PACS
75.50.Ee Antiferromagnetics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy

Correlations between magnetic and electrical orderings in multiferroic manganites (invited)

M. Fiebig, Th. Lottermoser, M. K. Kneip, and M. Bayer

J. Appl. Phys. 99, 08E302 (2006); http://dx.doi.org/10.1063/1.2172198 (5 pages) | Cited 12 times

Online Publication Date: 21 April 2006

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The multiferroic rare-earth compounds RMnO3 with R = Ho–Yb are shown to be the source of “gigantic” magnetoelectric effects. Application of static magnetic or electric field induces a phase transition with antiferromagnetic reordering of the Mn3+ sublattice and ferromagnetic ordering in the rare-earth sublattices. An imbalance of the Mn3+–R3+ superexchange induced by the ferroelectric distortion is revealed as the microscopic origin of the magnetoelectric effect.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Ferroelectricity induced by incommensurate magnetism (invited)

A. Brooks Harris

J. Appl. Phys. 99, 08E303 (2006); http://dx.doi.org/10.1063/1.2177392 (6 pages) | Cited 5 times

Online Publication Date: 27 April 2006

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Ferroelectricity has been found to occur in several insulating systems, such as TbMnO3 and Ni3V2O8 which have more than one phase with incommensurately modulated long-range magnetic order. Here we give a phenomenological model which relates the symmetries of the magnetic structure as obtained from neutron diffraction to the development and orientation of a spontaneous ferroelectric moment induced by the magnetic ordering. This model leads directly to the formulation of a microscopic spin-phonon interaction which explains the observed phenomena. The results are given in terms of gradients of the exchange tensor with respect to generalized displacements for the specific example of NVO. It is assumed that these gradients will now be the target of first-principles calculations using the LDA+U or related schemes.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.-e Ferroelectricity and antiferroelectricity
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
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