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

Abstract

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.