Enrichment of magnetoelectric effect in the hexagonal BaTi1-xCoxO3 artificial type-II multiferroics by defects

• Published in: Journal of magnetism and magnetic materials Vol. 529; p. 167927
• Main Authors: Esther Rubavathi, P., Rahul, M.T., Kalarikkal, Nandakumar, Das Adhikary, Gobinda, Sundarakannan, B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2021; Elsevier BV
• Subjects: Barium titanates; Broken symmetry; Cobalt; Coupling coefficients; Energy storage density; Ferroelectric materials; Ferroelectricity; Ferromagnetism; Hexagonal phase; Magnetic properties; Magnetoelectric properties; Multiferroic materials; Oxidation; Rietveld refinement; Spectral studies; Stoichiometry; Valence; Spectral studies; Rietveld refinement; Energy storage density; Magnetoelectric properties; Magnetic properties
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2021.167927

•An enrichment of ME coupling coefficient achieved in artificial BaTi1-xCoxO3 multiferroics.•Type-I multiferroic material converted into Type-II multiferroic material through structure transition.•Rapid arrival of hexagonal phase (P63/mmc) formed and it confirmed by HREM & SAED patterns.•Origin of magnetic and magnetoelectric coupling explained using defect engineering.•High value of energy efficiency reported in BaTi0.99Co0.01O3. Artificial magnetoelectric material with enrichment of magnetoelectric (ME) coupling coefficient was achieved via mixed-oxide route in cobalt substituted BaTiO3 multiferroics. The observed large ME coupling coefficient induced by spin–orbit interaction through the symmetry breaking due to the off-stoichiometry oxygen. Structural details extracted from the Rietveld refinement indicate the rapid arrival of a single hexagonal phase (P63/mmc) at the expense of the tetragonal phase (P4mm) above x = 0.03. SAED patterns evidence to the structural coexistence, morphotropic phase boundary (MPB), (P4mm + P63/mmc) in x = 0.01 and 0.03 while hexagonal phase alone in x ≥ 0.05. Core-level XPS spectrum of Ba(3d), Ti (2p), Co (2p), O (1s) evidences the occurrence of the single oxidation state of Ba ion (Ba2+) and aliovalent of Ti (Ti4+ and Ti3+), Co (Co3+ and Co2+) and O (O2− and O1−) ions respectively. The weakening of ferroelectric loops arises from the formation of the non-ferroelectric hexagonal phase by the non-stoichiometric oxygen. For the first time, a high value of energy efficiency of 54.7% was achieved in the BaTi0.99Co0.01O3 sample. The ferromagnetism originated from the contributions of the super-exchange interaction of Co3+(octahedral)-O2−-Co3+(pentahedral) and double-exchange interaction (Co2+-O2−-Co3+) Among all the samples, an excellent magnetoelectric coupling coefficient (αME) value of 29.6 mV/cm Oe is attained in the hexagonal BaTi0.93Co0.07O3 sample.