Tunable multifunctionality in BaTiO3–La0.835Na0.165MnO3 composites: from UV-to-visible light absorption and nonmagnetism to room-temperature ferromagnetism

Abstract

The composites of ferroelectric BaTiO₃ and ferromagnetic La_0.835Na_0.165MnO₃, denoted as (1−x)BaTiO₃:(x)La_0.835Na_0.165MnO₃ (x = 0, 10, 20, 30, 50, 100 wt%), were prepared using the conventional solid-state reaction method. This work investigates the effect of magnetic inclusion in a nonmagnetic matrix. The synthesized nonmagnetic BaTiO₃ majorly crystallized in a ferroelectric tetragonal structure belonging to the P4mm space group, while the magnetic inclusion La_0.835Na_0.165MnO₃ exhibited phase segregation into a rhombohedral lattice belonging to the Rc space group and a monoclinic lattice belonging to a La_0.9MnO₃-like deficient structure of the I12/a1 space group. The resulting composites were immiscible solid solutions composed of Ti-deficient BaTiO₃ and A-site-deficient La_0.835Na_0.165MnO₃. BaTiO₃ and La_0.835Na_0.165MnO₃ were morphologically distinct, with contrasting grain sizes and distributions. Composites showed a loosely bound immiscible grain distribution. The mixing of a nonmagnetic insulator and a ferromagnetic metal/semiconductor endowed the composites with unique optical properties. The band gap was effectively tuned from the ultraviolet to the visible region of the electromagnetic spectra. The composites exhibited a large Urbach energy. BaTiO₃ in its non-stoichiometric form was found to be a weak ferromagnet at room temperature and exhibited spin-glass-like frustration at low temperatures. La_0.835Na_0.165MnO₃ showed a double magnetic transition due to structural phase segregation. The composites showed robust ferromagnetism at room temperature, inheriting it from the magnetic component La_0.835Na_0.165MnO₃. The salient ferroelectricity of BaTiO₃ disappeared in the composites due to large leakage currents. However, at low bias voltages, a leaky ferroelectric nature with ferromagnetism existed at room temperature for the x = 10% specimen, making it a photosensitive, multiferroic, magnetoelectric composite oxide suitable for room-temperature applications.