Abstract
Epitaxial BiFeO3 thin films of 130nm were deposited by pulsed laser deposition (PLD) technique on La0.67Sr0.33MnO3 buffered SrTiO3 (001) substrate at various temperatures under different ambient oxygen pressures. Reciprocal space mapping reveals that, with decreasing temperature and oxygen pressure, the broadly reported monoclinic phase (MA) of BiFeO3 thin film initially transforms to a tetragonal phase (T1) with c/a =1.05 (1) in a narrow girth of deposition condition and then to a super-tetragonal phase (T2) with giant c/a = 1.24 (1), as confirmed by reciprocal space mapping using high resolution x-ray diffraction. The surface morphology of the films reveals the island growth of the BiFeO3 films deposited at low temperatures. We propose that the transformation from monoclinic to the super-tetragonal phase is essentially due to the manifestation of excess local strain as a result of the island growth. This study offers a recipe to grow the super-tetragonal phase of BiFeO3, with giant c/a =1.24 (1) which exhibits exceptionally large ferroelectric polarization, on ferromagnetic layer La0.67Sr0.33MnO3. This phase of BiFeO3 can be utilized for the ferroelectric control of magnetism at the interface of BiFeO3 and La0.67Sr0.33MnO3.
Highlights
Magnetoelectric multiferroics have attracted considerable interest due to their potential applications in multifunctional devices, such as information storage, spintronics, and sensors, where the magnetization can be tuned by the electric field and ferroelectric polarization through the magnetic field.[1–3]
We show that the broadly reported monoclinic phase (MA) of epitaxial BFO thin films initially transforms to a tetragonal phase (T1) with c/a =1.05 (1) and to a super-tetragonal phase (T2) with c/a = 1.24 (1), as the deposition temperature is lowered
We have presented the temperature controlled evolution of the various ferroelectric phases of BFO films on LSMO buffered STO (001) substrate using pulsed laser deposition technique
Summary
Magnetoelectric multiferroics have attracted considerable interest due to their potential applications in multifunctional devices, such as information storage, spintronics, and sensors, where the magnetization can be tuned by the electric field and ferroelectric polarization through the magnetic field.[1–3] In this perspective, BiFeO3 has become a canonical compound of interest due to the scarcity of thermodynamically stable single phase magnetoelectric multiferroics at room temperature.[4,5] Bulk. In BiFeO3/La1-xSrxMnO3 (BFO/LSMO) heterostructures, the coupling between AFM and FE order parameters of BFO offers an additional degree of freedom to control the magnetization of the LSMO layer via switching the ferroelectric polarization of BFO. The ME coupling at the interface of LSMO and the super-tetragonal phase of BFO with exceptionally high ferroelectric polarization (∼150μC/cm2), remains unexplored as it is thorny to introduce this phase on LSMO layer. Recent density functional studies predict the realization of ferroelectric control of magnetization by means of exchange bias at the interface of La0.67Sr0.33MnO3 (LSMO) and super-tetragonal phase of BFO.[28,29]. We present a pathway of introducing different ferroelectric phases of BiFeO3 epitaxial thin films on the top of a half-metallic ferromagnetic layer of La0.67Sr0.33MnO3 (LSMO), grown on STO (001) substrate by controlling both deposition temperature and ambient oxygen pressure. The ferroelectric switching in the super-tetragonal phase was confirmed by the observation of piezoresponse force microscopy (PFM) hysteresis and 1800 phase contrast upon cycling applied voltage
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