A large polarization in Ce-modified bismuth ferrite thin films effects on the ferroelectric and magnetic properties of chemical solution deposited Bi Fe O 3 thin films Several experimental methods to measure ferroelectric hysteresis loops and to extract polarization values are compared for thin films with significant losses and different magnitudes of polarization. The analysis allows the determination of the most appropriate frequency range and technique to extract reliable values of the remanent polarization in materials with low polarization and high leakage. Examples include multiferroic YMnO 3 and Bi 0.9 La 0.1 NiMnO 6 thin films.
Ferroelectric (FE) and ferromagnetic (FM) materials engineered in horizontal heterostructures allow interface-mediated magnetoelectric coupling. The so-called converse magnetoelectric effect (CME) has been already demonstrated by electric-field poling of the ferroelectric layers and subsequent modification of the magnetic state of adjacent ferromagnetic layers by strain effects and/or free-carrier density tuning. Here we focus on the direct magnetoelectric effect (DME) where the dielectric state of a ferroelectric thin film is modified by a magnetic field. Ferroelectric BaTiO3 (BTO) and ferromagnetic CoFe2O4 (CFO) oxide thin films have been used to create epitaxial FE/FM and FM/FE heterostructures on SrTiO3(001) substrates buffered with metallic SrRuO3. It will be shown that large ferroelectric polarization and DME can be obtained by appropriate selection of the stacking order of the FE and FM films and their relative thicknesses. The dielectric permittivity, at the structural transitions of BTO, is strongly modified (up to 36%) when measurements are performed under a magnetic field. Due to the insulating nature of the ferromagnetic layer and the concomitant absence of the electric-field effect, the observed DME effect solely results from the magnetostrictive response of CFO elastically coupled to the BTO layer. These findings show that appropriate architecture and materials selection allow overcoming substrate-induced clamping in multiferroic multi-layered films.
We report on the growth and functional characterization of epitaxial thin
films of the multiferroic YMnO3. We show that using Pt as a seed layer on
SrTiO3(111) substrates, epitaxial YMnO3 films (0001) textured are obtained. An
atomic force microscope has been used to polarize electric domains revealing
the ferroelectric nature of the film. When a Permalloy layer is grown on top of
the YMnO3(0001) film, clear indications of exchange bias and enhanced
coercivity are observed at low temperature. The observation of coexisting
antiferromagnetism and electrical polarization suggests that the biferroic
character of YMnO3 can be exploited in novel devices.Comment: 15 pages, 4 figures, Applied Physics Letters (in press
We report on the growth and characterization of epitaxial thin films of orthorhombic YMnO3. It is found that a ferroelectric polarization exists along c-axis (Pc∼90 nC/cm2) and a magnetic field induces the development of a ferroelectric polarization along a-axis (Pa) while suppressing Pc. This field-induced switching is consistent with the existence of a cycloidal magnetic order in YMnO3. This finding evidences that a noncollinear spin arrangement in thin films allows switchable electrical polarization and of tunability of their dielectric response by magnetic field.
We have studied the field, frequency, and amplitude dependence of the ac susceptibility on a single crystal of the electron-doped superconductor Prl 85Ceo»Cu04~. We show that a thermally activated flux motion over effective energy barriers U( T, H) = Uo(1 -T/T, )K,with Uo =40 meV, can account for the dc-field and frequency effects. The amplitude dependence of the ac response in this superconducting system is discussed and it is argued that it is a signature of the critical state.
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