Giant Spin-Driven Ferroelectric Polarization in BiFeO₃ at Room Temperature

Investigation of new magnetoelastic and magnetic transitions accompanied with magnetoelectric coupling in [Formula: see text] multiferroic

A new multiferroic solid solution [Formula: see text] has been developed and characterized for structure, phase transition, magnetoelectric and magnetoelastic coupling. Temperature dependent measurement of dc-magnetization [Formula: see text] on [Formula: see text] ceramic shows two magnetic transitions one around [Formula: see text]42 K and the second at [Formula: see text]130 K. The real part of dielectric permittivity exhibits step like change at the magnetic anomaly temperature ([Formula: see text]130 K) which indicates the presence of magnetoelectric coupling. The change in the value of dielectric permittivity on the application of magnetic field confirms the presence of magnetoelectric coupling in [Formula: see text] ceramic. The room temperature polarization (P)-electric field (E) hysteresis loop measurement shows week ferroelectric nature of sample while the magnetization (M) versus magnetic field (H) measurement suggest weakly ferromagnetic character. The ferroelectric nature of sample was further confirmed by calculating remanent polarization using PUND measurement. The Rietveld structural analysis of low temperature x-ray powder diffraction data does not reveal any crystallographic phase transition in terms of peak splitting or new reflections. However, temperature dependence of lattice parameters, tetragonality, unit cell volume, [Formula: see text] octahedral tilt angle ([Formula: see text]), [Formula: see text] bond length and [Formula: see text] bond angles reveal discontinuous changes at both the magnetic transitions observed in temperature dependence of magnetization. This confirms that both the magnetic anomalies (around [Formula: see text]42 K and [Formula: see text]130 K) exhibit magnetoelastic coupling accompanied with isostructural transitions.

Low-energy spin dynamics of orthoferrites AFeO3 (A = Y, La, Bi)

YFeO₃ and LaFeO₃ are members of the rare-earth orthoferrites family with Pbnm space group. Using inelastic neutron scattering, the low-energy spin excitations have been measured around the magnetic Brillouin zone center. Splitting of magnon branches and finite magnon gaps (∼2 meV) are observed for both compounds, where the Dzyaloshinsky-Moriya interactions account for most of this gap with some additional contribution from single-ion anisotropy. We also make comparisons with multiferroic BiFeO₃ (R3c space group), in which similar behavior was observed. By taking into account all relevant local Dzyaloshinsky-Moriya interactions, our analysis allows for the precise determination of all experimentally observed parameters in the spin-Hamiltonian. We find that different properties of the Pbnm and R3c space group lead to the stabilization of a spin cycloid structure in the latter case but not in the former, which explains the difference in the levels of complexity of magnon band structures for the respective compounds.

BiFeO3(00l)/LaNiO3/Si thin films with enhanced polarization: an all-solution approach

Multiferroic BiFeO₃ (BFO) thin films with a thickness larger than 400 nm are grown on solution-derived LaNiO₃ coated Si substrates via chemical solution deposition.