Giant magnetoelectric effect induced by intrinsic surface stress in ferroic nanorods

Abstract

The general approach for the consideration of the magnetoelectric effects in ferroic nanorods is proposed in the framework of the phenomenological theory. The intrinsic surface stress, magneto-and electrostriction, as well as piezoelectric and piezomagnetic effects are included in the free energy. The intrinsic surface stress under the curved nanoparticle surface is shown to play an important role in the shift of ferroelectric and ferromagnetic transition temperatures and appearance of built-in magnetic and electric fields, which are inversely proportional to the nanorod radius. We consider the case of quadratic and linear magnetoelectric coupling coefficients. The linear coupling coefficient is radius independent, whereas the quadratic ones include terms inversely proportional to the nanorod radius and thus strongly increase with radius decrease. We predicted that quadratic magnetoelectric coupling induces dielectric tunability increase by 2-50 times in the vicinity of ferromagnetic and ferroelectric phase transition points. The quadratic magnetoelectric coupling dramatically changes the phase diagrams of ferroic nanorods under their radius decrease. In particular, the second order phase transition may become the first one. Special attention is paid to the case when polarization, magnetization, and magnetoelectric couplings are induced by intrinsic surface stress in nanorods.

Size-induced enhanced magnetoelectric effect and multiferroicity in chromium oxide nanoclusters

“…4c) suggests that quadratic terms in E dominate the magnetoelectric behaviour. This is in agreement with the drastic increase of the quadratic magnetoelectric coefficient predicted in nanoclusters 6 as well as with the poor symmetry compatibility between weak ferromagnetism and linear magnetoelectric effect 20 . Yet, m does not vary as V 2 .…”

“…As seen in Fig. 6b, (V p t Cr ) À 1 also decreases exponentially with increasing t Cr , with a characteristic decay constant There is therefore experimental evidence that the two dipoles, p and m, share a common origin: epitaxial strain drives the value of the magnetic dipole m as well as that of the electric dipole p. The occurrence of a permanent electric polarisation under stress in paraelectric materials with non-zero coupling between lattice and electric order has indeed been predicted 6,7,37 and observed 8 in other systems. We thus conclude that the Cr 2 O 3 particles exhibit both a (weak) ferromagnetic order and a ferroelectric order.…”

“…This is consistent with recent experimental works 23,24 reporting a remnant magnetic moment in granular Cr 2 O 3 arising from magneto-elastic effects. Note that, following the model of Glinchuk et al 6 , non-zero magneto-elastic coefficients can explain the drastic enhancement of magnetoelectric properties we observe in strained Cr 2 O 3 clusters.…”

“…Strain engineering is envisioned as a possible route for improving magnetoelectric properties 2 with the predicted huge increase of the magnetoelectric coefficients 6 and even the appearance of new multiferroic phases for strained materials 6,7 . Small epitaxial structures, which can sustain much larger amounts of stress than the bulk, are thus worth exploring 8 .…”

New multiferroics based on EuxSr1−xTiO3 nanotubes and nanowires

“…The intrinsic surface stress can induce ferroelectricity, ferromagnetism and increase corresponding phase transition temperatures in conventional ferroelectrics and quantum paraelectric nanorods, nanowires [15,16,17,18,19] and binary oxides [20].The surface stress is inversely proportional to the surface curvature radius and directly proportional to the surface stress tensor (similar to Laplace surface tension). Thus, the intrinsic surface stress should depend both on the growth conditions and the surface termination morphology [21,22].…”