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Register a new userField induced changes in cycloidal spin ordering and coincidence between magnetic and electric anomalies in BiFeO3 multiferroic
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Added by
Bartlomiej Andrzejewski
Publication date
2012
fields
Physics
and research's language is
English
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The ZFC and FC magnetization dependence on temperature was measured for BiFeO3 ceramics at the applied magnetic field up to H=10T in 2K-1000K range. The antiferromagnetic order was detected from the hysteresis loops below the Neel temperature TN=646K. In the low magnetic field range there is an anomaly in M(H), probably due to the field-induced transition from circular cycloid to the anharmonic cycloid. At high field limit we observe the field-induced transition to the homogeneous spin order. From the M(H) dependence we deduce that above the field Ha the spin cycloid becomes anharmonic which causes nonlinear magnetization, and above the field Hc the cycloid vanishes and the system again exhibits linear magnetization M(H). The anomalies in the electric properties, which are manifested within the 640K-680K range, coincide to the anomaly in the magnetization M(T) dependence, which occurs in the vicinity of TN. We propose to ascribe this coincidence to the critical behaviour of the chemical potential, related to the magnetic phase transition.
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The magnetic-field-dependent spin ordering of strained BiFeO3 films is determined using nuclear resonant scattering and Raman spectroscopy. The critical field required to destroy the cycloidal modulation of the Fe spins is found to be significantly lower than in the bulk, with appealing implications for field-controlled spintronic and magnonic devices.
We propose a way to use electric-field to control the magnetic ordering of the tetragonal BiFeO3. Based on systematic first-principles studies of the epitaxial strain effect on the ferroelectric and magnetic properties of the tetragonal BiFeO3, we find that there exists a transition from C-type to G-type antiferromagnetic (AFM) phase at in-plane constant a ~ 3.905 {AA} when the ferroelectric polarization is along [001] direction. Such magnetic phase transition can be explained by the competition between the Heisenberg exchange constant J1c and J2c under the influence of biaxial strain. Interestingly, when the in-plane lattice constant enlarges, the preferred ferroelectric polarization tends to be canted and eventually lies in the plane (along [110] direction). It is found that the orientation change of ferroelectric polarization, which can be realized by applying external electric-field, has significant impact on the Heisenberg exchange parameters and therefore the magnetic orderings of tetragonal BiFeO3. For example, at a ~ 3.79 {AA}, an electric field along [111] direction with magnitude of 2 MV/cm could change the magnetic ordering from C-AFM to G-AFM. As the magnetic ordering affects many physical properties of the magnetic material, e.g. magnetoresistance, we expect such strategy would provide a new avenue to the application of multiferroic materials.
The paper deals with the hyperfine interactions observed on the 57Fe nucleus in multiferroic BiFeO3 by means of the 14.41-keV resonant transition in 57Fe, and for transmission geometry applied to the random powder sample. Spectra were obtained at 80 K, 190 K and at room temperature. It was found that iron occurs in the high spin trivalent state. Hyperfine magnetic field follows distribution due to the elliptic-like distortion of the magnetic cycloid. The long axis of the ellipse is oriented along <111> direction of the rhombohedral unit cell. The hyperfine magnetic field in this direction is about 1.013 of the field in the perpendicular direction at room temperature. This ratio diminishes to 1.010 at 80 K. Axially symmetric electric field gradient (EFG) on the iron atoms has the principal axis oriented in the same direction and the main component of the EFG is positive. Our results are consistent with the finding that iron magnetic moments are confined to the [1-21] crystal plane.
We have determined the full magnetic dispersion relations of multiferroic BiFeO3. In particular, two excitation gaps originating from magnetic anisotropies have been clearly observed. The direct observation of the gaps enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction and the single ion anisotropy. The DM interaction supports a strong magneto-electric coupling in this compound.
We report a temperature-dependent Raman and neutron scattering investigation of the multiferroic material bismuth ferrite BiFeO3 (BFO).
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