Cr, Mn, Co, Ni, and Cu were added to polycrystalline BiFeO3 films, and their influence on the ferroelectric, electrical, and magnetic properties was investigated. All the additives except Ni reduced the leakage current density in the high electric field region. The addition of Cu and Co decreased the coercive field without reducing remanent polarization. The addition of Co caused spontaneous magnetization at room temperature, which exhibited a large coercive field of 16kOe at 10K. It was revealed that Co addition suppressed the leakage current density, decreased the electric coercive field, and induced spontaneous magnetization and large magnetic coercivity.

Multiferroic Co-substituted BiFeO3 films were fabricated by chemical solution deposition method followed by post deposition annealing at various temperatures. The substitution of cobalt of B-sites for iron in BiFeO3 was promoted at relatively high temperatures. The B-site substitution by cobalt promoted increases in saturation magnetization and spontaneous magnetization. By substitution, leakage current density was suppressed in a high-electric-field region, and ferroelectric hysteresis (P–E) loops became measurable even at room temperature. The optimal annealing temperature for the coexistence of a high remanent polarization and a high remanent magnetization was 923 K having a high B-site substitution ratio of cobalt.

Non-radiative complete surface acoustic wave bandgap for finite-depth holey phononic crystal in lithium niobate Appl. Phys. Lett. 100, 061912 (2012) Investigation of dielectric and electrical properties of Mn doped sodium potassium niobate ceramic system using impedance spectroscopy J. Appl. Phys. 110, 104102 (2011) Determination of depolarization temperature of (Bi1/2Na1/2)TiO3-based lead-free piezoceramics J. Appl. Phys. 110, 094108 (2011) Finite element method simulation of the domain growth kinetics in single-crystal LiTaO3: Role of surface conductivity J. Appl. Phys. 110, 052016 (2011) Additional information on J. Appl. Phys. Both the ferroelectric and magnetic properties of polycrystalline BiFeO 3 films fabricated by chemical solution deposition were enhanced by adding small amounts of cobalt. Addition of 3 at. % cobalt to BiFeO 3 films increased the remanent polarization from 49 to 72 C / cm 2 and decreased the electric coercive field from 0.54 to 0.44 MV/ cm. The ferroelectricity degraded when the cobalt concentration exceeded 9 at. % due to the formation of the secondary phases of Bi 2 Pt. The saturation magnetization was drastically enhanced by the addition of cobalt up to 12 at. %. This is because the magnetic moments are not canceled locally since the differences of magnetic moment between B-sites. The saturation magnetization decreased when the cobalt content exceeded 15 at. %, thereby attributing to the formation of a nonmagnetic secondary phase of Bi 2 Pt. It is concluded that both ferroelectric and magnetic properties were enhanced, provided only small amount of cobalt were added to the films.

We fabricated 5 at.% Mn-added polycrystalline BiFeO 3 films and investigated the annealing temperature effect on structural, ferroelectric and magnetic properties. In the x-ray diffraction patterns, only the diffraction peaks due to the BiFeO 3 structure were observed and no secondary phase could be observed at annealing temperatures between 773 and 923 K. Adding Mn suppressed the leakage current density in the high electric field region when compared to pure BiFeO 3 films. The conduction mechanism of the Mn-added BiFeO 3 films was dominated by Ohmic conduction. Remanent polarization of the Mn-added polycrystalline BiFeO 3 films for an applied electric field of approximately 1.5 mV/cm was 63 μC/cm 2 for the specimen annealed at 773 K and 46 μC/cm 2 for the specimen annealed at 923 K, although the remanent polarization still exhibited a tendency to increase with an increase in the electric field. Spontaneous magnetization was obtained at high annealing specimens. This study revealed that the annealing temperature strongly affected the ferroelectric and magnetic properties in Mnadded polycrystalline BiFeO 3 films. In addition, by optimizing the annealing temperature, we realized multiferroics coexistent with spontaneous magnetization and spontaneous polarization at room temperature in the Mn-added polycrystalline BiFeO 3 film.

Co and Mn co-substituted BiFeO 3 films were prepared on Pt/Ti/SiO 2 /Si(100) substrates, and the effect of co-substitution on the structural, electric, and magnetic properties of the prepared films was systematically investigated. Cross-sectional transmission electron microscopy observations showed that the films were homogeneous; moreover, no magnetic secondary phases were observed in the films. Nano-beam energy-dispersive X-ray spectroscopy, carried out at various points in the films, revealed that Co and Mn were distributed in the films. Further, the average concentration of Bi, Co, Mn, and Fe was 59, 2, 2, 37 at.%, respectively; these values were almost consistent with the nominal composition of the precursor solution used. X-ray diffraction profiles of the films showed that the (012)-d-spacing decreased and (104) and (110) peaks merged into a single peak with increasing co-substitution content. The leakage current in films under high electric fields drastically decreased upon co-substitution without any degradation of ferroelectricity; moreover, this effect was also observed for single Mn-substituted materials. Saturation magnetization of the films monotonically increased with the co-substitution content, and this increase was quantitatively identical to that in the case of single Co-substituted materials. These results indicate that Co and Mn play significant roles in determining the properties of co-substituted BiFeO 3 films.