Infrared and magnetic characterization of the multiferroic Bi2FeCrO6 thin films in a broad temperature range (original) (raw)
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Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order
Journal of Materials Research, 2007
Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed X-ray diffraction and cross-section transmission electron microscopy analysis revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+ cation ordering along the [111] direction. The films contain no detectable magnetic iron oxide impurities and have the correct cationic average stoichiometry throughout their thickness. They however exhibit a slight modulation in the Fe and Cr compositions forming complementary stripe patterns, suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO films exhibit good ferroelectric and piezoelectric properties, in addition to magnetic properties at room temperature, as well as an unexpected crystallographic orientation dependence of their room temperature magnetic properties. Our results qualitatively confirm the predictions made using the ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along with the unpredicted existence of magnetic ordering at room temperature.
Physical Review B, 2008
Infrared reflectance spectra of an epitaxial Bi2FeCrO6 thin film prepared by pulsed laser deposition on LaAlO3 substrate were recorded between 10 and 900 K. No evidence for a phase transition to the paraelectric phase was observed, but some phonon anomalies were revealed near 600 K. Most of the polar modes exhibit only a gradual softening, which results in a continuous increase of the static permittivity on heating. It indicates that the ferroelectric phase transition should occur somewhere above 900 K. Magnetic measurements performed up to 1000 K, revealed a possible magnetic phase transition between 600 and 800 K, but the exact critical temperature cannot be determined due to a strong diamagnetic signal from the substrate. Nevertheless, our experimental data show that the B-site ordered Bi2FeCrO6 is one of the rare high-temperature multiferroics.
Journal of Applied Physics, 2009
The influence of the deposition pressure PO 2 and substrate temperature T S during the growth of Bi 2 FeCrO 6 thin films grown by pulsed laser deposition has been investigated. It is found that the high volatility of Bi makes the deposition very difficult and that the growth of pure Bi2FeCrO6 thin films on SrTiO 3 substrates is possible only in a narrow deposition parameter window. We find that the pure Bi 2 FeCrO 6 phase is formed within a narrow window around an oxygen pressure PO 2 =1.2×10 −2 mbar and around a substrate temperature T S =680 °C. At lower temperature or higher pressure, Bi 7.38 Cr 0.62 O 12+x _also called (b*Bi 2 O 3 )and Bi 2 Fe4O 9 /Bi 2 (Fe,Cr) 4 O 9+x phases are detected, while at lower pressure or higher temperature a (Fe,Cr) 3 O 4 phase forms. Some of these secondary phases are not well known and have not been previously studied. We previously reported Fe/Cr cation ordering as the probable origin of the tenfold improvement in magnetization at saturation of our Bi 2 FeCrO 6 film, compared to BiFeO 3 . Here, we address the effect of the degree of cationic ordering on the magnetic properties of the Bi 2 FeCrO 6 single phase. Polarization measurements at room temperature reveal that our Bi2FeCrO6 films have excellent ferroelectric properties with ferroelectric hysteresis loops exhibiting a remanent polarization as high as 55-60 µC/cm 2 along the pseudocubic (001) direction.
Journal of Applied Physics, 2009
The influence of the deposition pressure PO 2 and substrate temperature T S during the growth of Bi 2 FeCrO 6 thin films grown by pulsed laser deposition has been investigated. It is found that the high volatility of Bi makes the deposition very difficult and that the growth of pure Bi2FeCrO6 thin films on SrTiO 3 substrates is possible only in a narrow deposition parameter window. We find that the pure Bi 2 FeCrO 6 phase is formed within a narrow window around an oxygen pressure PO 2 =1.2×10 −2 mbar and around a substrate temperature T S =680 °C. At lower temperature or higher pressure, Bi 7.38 Cr 0.62 O 12+x _also called (b*Bi 2 O 3 )and Bi 2 Fe4O 9 /Bi 2 (Fe,Cr) 4 O 9+x phases are detected, while at lower pressure or higher temperature a (Fe,Cr) 3 O 4 phase forms. Some of these secondary phases are not well known and have not been previously studied. We previously reported Fe/Cr cation ordering as the probable origin of the tenfold improvement in magnetization at saturation of our Bi 2 FeCrO 6 film, compared to BiFeO 3 . Here, we address the effect of the degree of cationic ordering on the magnetic properties of the Bi 2 FeCrO 6 single phase. Polarization measurements at room temperature reveal that our Bi2FeCrO6 films have excellent ferroelectric properties with ferroelectric hysteresis loops exhibiting a remanent polarization as high as 55-60 µC/cm 2 along the pseudocubic (001) direction.
Electric and Magnetic Properties of Multiferroic BiFeO$_{3}$ and YMnO$_{3}$ Thin Films
IEEE Transactions on Magnetics, 2008
We grew rhombohedrally distorted BiFeO 3 and hexagonal YMnO 3 thin films on Pt/TiO 2 /SiO 2 /Si substrates via RF magnetron sputtering technique in a pure oxygen atmosphere. BiFeO 3 and YMnO 3 targets were self-made by the usual solid-state reaction method. We investigated the effects of deposition temperature upon crystalline structure, surface morphology, magnetization, and electrical polarization of BiFeO 3 and YMnO 3 thin films. The crystalline structure was studied by X-ray diffraction, and the topography of film surface was analyzed by atomic force microscopy. We also conducted measurements of ferroelectric and ferromagnetic hysteresis loops to study the electrical and magnetic behavior of the samples. Polarization, as a function of electric field in capacitor structures based on our BiFeO 3 films, shows hysteretic behavior with a coercive field of 54 kV/cm and a remanent polarization of 21 C/cm 2 ; whereas, YMnO 3 films show hysteretic behavior with coercive field of 2.4 kV/cm, remanent polarization of 1.2 C/cm 2 , and saturation polarization of 3.5 C/cm 2. Magnetization measurements of the BiFeO 3 films evidence weak ferromagnetism, that can be related to the presence of a small quantity of ferromagnetic impurities.
Integrated Ferroelectrics, 2008
Experimental results on Bi2FeCrO6 (BFCO) epitaxial films deposited by laser ablation on SrTiO3 substrates are presented. It has been theoretically predicted using first-principles density functional theory that BFCO is ferrimagnetic (with a magnetic moment of 2muB per formula unit) and ferroelectric (with a polarization of ~80 microC/cm2 at 0K). The crystal structure investigated using X-ray diffraction shows that the films are epitaxial with a high degree of crystallinity. Chemical analysis carried out by X-ray Microanalysis and X-ray Photoelectron Spectroscopy indicates the correct cationic stoichiometry in the BFCO layer, namely (Bi:Fe:Cr = 2:1:1). Cross-section high-resolution transmission electron microscopy images together with selected area electron diffraction confirm the crystalline quality of the epitaxial BFCO films with no identifiable foreign phase or inclusion. The multiferroic character of BFCO is proven by piezoresponse force microscopy (PFM) and magnetic measurements showing that the films exhibit ferroelectric and magnetic hysteresis at room temperature. The local piezoelectric measurements show the presence of ferroelectric domains and their switching at the sub-micron scale.
Journal of Applied Physics, 2012
Aurivillius phase Bi 5 Ti 3 Fe 0.7 Co 0.3 O 15 (BTF7C3O) thin films on a-quartz substrates were fabricated by a chemical solution deposition method and the room temperature ferroelectric and magnetic properties of this candidate multiferroic were compared with those of thin films of Mn 3þ substituted, Bi 5 Ti 3 Fe 0.7 Mn 0.3 O 15 (BTF7M3O). Vertical and lateral piezoresponse force microscopy (PFM) measurements of the films conclusively demonstrate that BTF7C3O and BTF7M3O thin films are piezoelectric and ferroelectric at room temperature, with the major polarization vector in the lateral plane of the films. No net magnetization was observed for the inplane superconducting quantum interference device (SQUID) magnetometry measurements of BTF7M3O thin films. In contrast, SQUID measurements of the BTF7C3O films clearly demonstrated ferromagnetic behavior, with a remanent magnetization, B r , of 6.37 emu/cm 3 (or 804 memu/g), remanent moment ¼ 4.99 Â 10 À5 emu. The BTF7C3O films were scrutinized by xray diffraction, high resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis mapping to assess the prospect of the observed multiferroic properties being intrinsic to the main phase. The results of extensive micro-structural phase analysis demonstrated that the BTF7C3O films comprised of a 3.95% Fe/Co-rich spinel phase, likely CoFe 2 À x Ti x O 4 , which would account for the observed magnetic moment in the films. Additionally, x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) imaging confirmed that the majority of magnetic response arises from the Fe sites of Fe/Co-rich spinel phase inclusions. While the magnetic contribution from the main phase could not be determined by the XMCD-PEEM images, these data however imply that the Bi 5 Ti 3 Fe 0.7 Co 0.3 O 15 thin films are likely not single phase multiferroics at room temperature. The PFM results presented demonstrate that the naturally 2D nanostructured Bi 5 Ti 3 Fe 0.7 Co 0.3 O 15 phase is a novel ferroelectric and has potential commercial applications in high temperature piezoelectric and ferroelectric memory technologies. The implications for the conclusive demonstration of ferroelectric and ferromagnetic properties in single-phase materials of this type are discussed. V
Journal of Physics-condensed Matter, 2012
We report recent developments in the growth and characterization of epitaxial Bi 2 FeCrO 6 (BFCO) thin films. The body of experimental data stemming mostly from our investigations, and also considering the few available reports from other groups, allows us to explain the origin(s) of the thickness dependence of the multiferroic properties observed. A drastic reduction of the films' magnetization is observed for film thicknesses larger than 80 nm. This decrease in magnetization is attributed to the formation of defects, such as antisites and antiphase boundaries, in the BFCO films. The change in magnetization is accompanied by a BFCO cell expansion, a consequence of the volume increase of the oxygen octahedra surrounding the Fe cations induced by the defects. BFCO films are ferroelectric for all the thicknesses investigated, ferroelectricity being only moderately affected by the film thickness.
Journal of Materials Science: Materials in Electronics, 2015
Pure BiFeO3 perovskite thin films have been prepared on Pt-coated silicon substrates by chemical solution deposition at temperatures below 500ºC. Precursor solutions with and without Bi(III) excess have been used. Perovskite films without crystalline secondary phases, as detected by X-ray diffraction analysis, are obtained at the lowest temperature limit of 400ºC. However, the scanning electron micrographs of these films show surface microstructures formed by well defined grains surrounded by a fine grained phase, suggesting the appearance of a volume fraction of crystals in an early stage of crystallization. The films prepared with Bi(III) excess have better defined ferroelectric hysteresis loops than those without any excess, especially for the films annealed at 400ºC, which can be attributed to an improved connectivity of the ferroelectric phase. This together with the fact that leakage current densities in the films decrease with decreasing the processing temperature, make that the BiFeO3 films prepared with Bi(III) excess and annealed at 400ºC and 450ºC can be poled at room temperature, obtaining an effective switching of the ferroelectric polarization with the electric field. Remanent polarization values of PR10 C/cm 2 and PR60 C/cm 2 with coercive fields of EC205 kV/cm and 235 kV/cm were obtained for the films prepared at 400ºC and 450ºC, respectively. The demonstration of the functionality at room temperature of these low temperature processed undoped BiFeO3 thin films increases the interest in these materials for their integration in multiferroic devices.
Epitaxial BiFeO3 Multiferroic Thin Film Heterostructures
Science, 2003
Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO 3 , is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.