Magneto-induced polarization enhancement and magneto-dielectric properties in oxygen deficient La0.67Sr0.33MnO3-/BaTiO3 composite film

Abstract

Magnetoelectric composite film is an important type of multiferroic materials, which is usually composed of typical ferromagnetic and ferroelectric materials. For the ferroelectric layer, BaTiO3 (BTO) attracts much attention due to its lead-free characteristic. For the ferromagnetic layer, doped manganite (R1-xAxMnO3) has been a good candidate for designing the advanced multiferroic films. Multiple interactions among the freedom degrees of charge, orbital, spin and lattice inside the doped manganite bring many additional properties into the manganite based composite films. At present, most of researches of manganite/BTO focus on the stoichiometric oxygen ion in manganite. Considering the fact that the oxygen deficiency can remarkably adjust the properties of manganite itself and relevant heterostructure by the interface effect, abnormal magnetoelectric properties are expected in an oxygen deficient manganite/BTO composite film. In this work, a composite film composed of BTO and oxygen deficient La0.67Sr0.33MnO3- (LSMO) is deposited on LaAlO3 001 substrate by the pulsed laser deposition method, and the effects of magnetic field on the properties of polarization and dielectric in a temperature range of 20-300 K are investigated. The X-ray diffraction pattern reveals good epitaxial growth of this bilayer film. The upper LSMO film exhibits semiconductive characteristic (dR/dT 0) in a temperature range of 20-300 K. Magnetization curves indicate that the LSMO keeps ferromagnetic state without any magnetic phase transition in this temperature range. When applying a magnetic fields of 0.8 T, the resistance in LSMO is observed to decrease. The changing rate MR=|R0.8 T-R0 T|/R0 T decreases from 45.28% at 30 K to 0.15% at 300 K. This composite film exhibits remarkable temperature-dependent magneto-induced ferroelectric and dielectric change. It is found that the remanent polarization (Pr) and coercive electric field (Ec) are enhanced by the 0.8 T magnetic field. The maximum changing rates of Pr and Ec are 111.9% and 89.6% at the temperatures of 40 K and 60 K, respectively. The magnetic field enhances the dielectric constant , but suppresses the dielectric loss tan . The maximum changing rates of and tan both occur at 60 K with the values of 300% and 50.9%. The temperature at which appear the maximum magneto-induced relative changes of polarization and dielectric parameters is accordant with the temperature at which occurs the peak value of magnetoresistance, which indicates a charge-based coupling in this heterojunction. A potential mechanism is that the magnetic field promotes the degree of parallelism of local spin magnetic moment of Mn ion, and produces an indirect effect on BTO layer by the spin-obital coupling and interface effect. Our findings make the oxygen deficient LSMO/BTO heterojunction promising for the design of multiferroic devices.