Interaction of multiferroic properties and interfaces in hexagonal LuMnO₃ ceramics

A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, off-stoichiometric LuMnO3 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 Mn3+ trimmers in basal plane show decreasing trends. It was found that increasing the annealing time improves the 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 the secondary phase or internal interfaces like ferroelectric (FE) domain walls. Magneto-dielectric coupling at T N is preserved in off-stoichiometric ceramics. The presence of a low temperature anomaly of the dielectric constant is correlated to the composition of the solid solution in off-stoichiometric ceramics. Large FE domains are observed in piezoresponse force microscopy (PFM) images of doped and un-doped ceramics, whereas atomic structure analysis indicates the parallel formation of nano-sized FE domains. A 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

Peculiar Magnetoelectric Coupling in BaTiO3:Fe-113 ppm Nanoscopic Segregations

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 Delta M/M approximate to 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

Thickness dependence of microstructure in thin La0.7Sr0.3MnO3 films grown on (100) SrTiO3 substrate

This study investigates the nanostructure of perovskite thin films, and its influence on magnetic properties. Epitaxial thin films of perovskite La0.7Sr0.3MnO3 with thickness ranging from 13.5 nm to 320 nm were deposited on SrTiO3 (1 0 0) substrates using pulsed laser deposition techniques. X-ray diffraction, along with high-resolution transmission electron microscopy (HRTEM) investigations were carried out, and showed the presence of a second, La-rich phase in thick film. Scanning electron microscopy analysis showed thinner films to have smooth surfaces, while thicker films presented large triangular shapes emerging out of the film surface. Also HRTEM images revealed epitaxial growth for thinner films. Thicker films grow with numerous misfit dislocations leading to columnar structure, where the thickest film presents branched structure with an intermediate La-rich layer. Lattice mismatch, diffusion of Mn ions into the substrate and substituting Ti ions are known as sources of strain in films near interfaces. Magnetic properties in the structure mentioned are described by double-exchange interaction, which is very sensitive to local structure. Hence, the nanostructure of films reported here has a remarkable effect on their magnetic properties.- This work was developed in the scope of the project CICECO-Aveiro Institute of Materials (Ref. FCT UID / CTM /50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. We would like to thank the financial support from the FCT project PTDC/FIS/105416/2008 MULTIFOX and PTDC/CTM/099415/2008 grants and FCT project SFRH/BD/51140/2010 to access all microscopes in pole of electron microscopy in Aveiro University. They are also grateful to professor Joaquim Manuel Vieira for his fruitful discussions on TEM analysis and results.info:eu-repo/semantics/publishedVersio

Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films

Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (T-STO), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness <= 100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below T-STO. However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the 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 full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour