Proximate transition temperatures amplify linear magnetoelectric coupling in strain-disordered multiferroicBiMnO3

Abstract

We report a giant linear magnetoelectric coupling in strained BiMnO3 thin films in which the disorder associated with an islanded morphology gives rise to extrinsic relaxor ferroelectricity that is not present in bulk centrosymmetric ferromagnetic crystalline BiMnO3. Strain associated with the disorder is treated as a local variable which couples to the two ferroic order parameters, magnetization M and polarization P . A straightforward "gas under a piston" thermodynamic treatment explains the observed correlated temperature dependencies of the product of susceptibilities and the magnetoelectric coefficient together with the enhancement of the coupling by the proximity of the ferroic transition temperatures close to the relaxor freezing temperature. Our interpretation is based on a trilinear coupling term in the free energy of the form L · ( P × M ) where L is a hidden antiferromagnetic order parameter, previously postulated by theory for BiMnO3. This phenomenological invariant not only preserves inversion and time reversal symmetry of the straininduced interactions but also explains the pronounced linear magnetoelectric coupling without using the more conventional higher order biquadratic interaction proportional to ( P · M )2 .

Piezoelectric, magnetic and magnetoelectric properties of a new lead-free multiferroic (1-x) Ba0.95Ca0.05Ti0.89Sn0.11O3—(x) CoFe2O4 particulate composites

“…Single-phase materials with intrinsic ME coupling are understudied because of their weak ME effect at or near room temperature, which restricts the applications [12]. Indeed, the ferroelectric mechanism, which requires formally empty d orbitals, in contrast to the ferromagnetic mechanism, which requires partially filled d orbitals [12], [13].…”

“…Single-phase materials with intrinsic ME coupling are understudied because of their weak ME effect at or near room temperature, which restricts the applications [12]. Indeed, the ferroelectric mechanism, which requires formally empty d orbitals, in contrast to the ferromagnetic mechanism, which requires partially filled d orbitals [12], [13]. On the other hand, synthetic multiferroic composites with various forms of connectivity, such as particulate ceramic (0-3) [14], laminates/films (2-2) [15], [16], and rod/fibers core-shell (1-3) [17], exhibit an excellent extrinsic ME coupling created by an elastic ferroelectric-ferromagnetic interfacial interaction combining high magnetostriction and a large piezoelectric response.…”

Multiferroic CoFe2O4–Ba0.95Ca0.05Ti0.89Sn0.11O3 Core–Shell Nanofibers for Magnetic Field Sensor Applications

“…Two types of magnetoelectric materials exist: (i) Single-phase multiferroic materials have electric and magnetic fields intrinsically coupled. , However, magnetoelectric couplings in these types of materials are typically very weak . (ii) Multiphase composites consist of distinct piezoelectric and magnetostrictive phases that are spatially segregated and interconnected through an interface.…”