A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, off-stoichiometric LuMnO 3 oxide is presented. By increasing Mn content the a-axis constant and volume of the unit cell, the antiferromagnetic (AFM) Néel temperature, T N , and frustration factor of the frustrated Mn 3+ trimmers in basal plane show decreasing trends. It was found that increasing annealing time improves properties of the lattices and progressively eliminates secondary phases for compositions within the solid solution stability limits. A magnetic contribution below T N is observed for all samples. Two regimes of magnetization below and above 45 K were observed in the AFM state. The magnetic contribution below T N is assigned to either secondary phase or internal interfaces like ferroelectric (FE) domain walls. Magneto-dielectric coupling at T N is preserved in offstoichiometric ceramics. The presence of a low temperature anomaly of the dielectric constant is correlated to composition of the solid solution in off-stoichiometric ceramics. Large FE domains are observed in PFM images of doped and un-doped ceramics, whereas atomic structure analysis indicates parallel formation of nano-sized FE domains. Combination of measured properties and microscopy images of micron-and nano-sized domains ascertain the role of lattice distortion and stability of solid solution on multiferroic properties.

Self-doping of h-LuMn x O 3± (0.92≤x≤1.12) phase and changes of sintering time are applied to investigate the formation and annihilation of antiphase ferroelectric (FE) domains in bulk ceramics. The increasing of annealing time in sintering results in growth of FE domains which depends on type of vacancy, 6-fold vortices with dimensions of the order of 20 microns being observed. Interference of planar defects of the lattice with the growth of topological defects shows breaking of 6-fold symmetry in the self-doped ceramics. The role of grain boundaries on the development of topological defects has studied. Dominance of the atypical FE domain network in very defective h-LuMn x O 3± lattices saturated with Mn vacancies (x< 1) was also identified in the current study. After long annealing time scattered closed-loops of nanodimensions are often observed isolated inside large FE domains with opposite polarization. Restoring of the polarization after alternative poling with opposite electrical fields is observed in FE domains. Stress/strain in the lattice driven either by planar defects or chemical inhomogeneity results in FE polarization switching in nano scale and further formation of nano-vortices, detailed investigation having been carried out by electron microscopy. Pinning of FE domains to planar defects is explored in the present microscopy analysis and nano-scale observation of lattices is used to explain features of the ferroelectricity revealed in PFM images of the ceramics.

Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thickness ranging from 20 nm up to 330 nm, were deposited on (100)-oriented strontium titanate (STO) substrates by pulsed laser deposition, and their structure and morphology characterized at room temperature. Magnetic and electric transport properties of the asprocessed thin films reveal an abnormal behavior in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (TSTO) and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Up to 100 nm LSMO thin films, an in-excess magnetization and pronounced changes in the coercivity are evidenced, achieved through the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below TSTO. Contrarily, for thicker LSMO thin films, above 100 nm, an in-defect magnetization is observed. This reversed behavior can be understood within the emergence in the upper layer of the film, observed by high resolution transmission electron microscopy, of a branched structure needed to relax elastic energy stored in the film which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a fully suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behavior.

We report polycrystalline BaTiO3 with cooperative magnetization behavior associated with the scarce presence of about 113 atomic ppm of Fe ions, clearly displaying magnetoelectric coupling with significant changes in magnetization (up to ΔM/M ≈ 32%) at the ferroelectric transitions. We find that Fe ions are segregated mostly at the interfaces between grain boundaries and an Fe-rich phase, forming a self-composite with high magnetoelectric coupling above room temperature. We compare our results with ab initio calculations and other experimental results found in the literature, proposing mechanisms that could be behind the magnetoelectric coupling within the ferroelectric matrix. These findings open the way for further strategies to optimize interfacial magnetoelectric couplings.

Abstract:We report an effect of giant surface modification of a 5.6 nm thick BaTiO 3 film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under −20 V applied during scanning, resulting in the maximum strain of 160%. The threshold voltage for the surface modification is about 12 V. The modified topography is stable enough with time and slowly decays after poling with the rate~0.02 nm/min. Strong vertical piezoresponse after poling is observed, too. Combined measurements by SPM and piezoresponse force microscopy (PFM) prove that the poled material develops high ferroelectric polarization that cannot be switched back even under an oppositely oriented electric field. The topography modification is hypothesized to be due to a strong Joule heating and concomitant interface reaction between underlying Si and BaTiO 3 . The top layer is supposed to become ferroelectric as a result of local crystallization of amorphous BaTiO 3 . This work opens up new possibilities to form nanoscale ferroelectric structures useful for various applications.