100-nm-sized magnetic domain reversal by the magneto-electric effect in self-assembled BiFeO3/CoFe2O4 bilayer films

Magnetization reversal of [Co/Pd] perpendicular magnetic thin film dot on (Bi,La)(Fe,Co)O3multiferroic thin film by applying electric field

A multilayer structure with a high-quality (Bi,La)(Fe,Co)O3multiferroic thin film/[Co/Pd] perpendicular magnetic thin film dots was fabricated for demonstrating magnetization reversal of [Co/Pd] dots under an applied electric field. Although the magnetization direction of the multiferroic thin film was reversed under the electric field, the magnetic properties of the multiferroic thin films were generally low. If the multiferroic thin film in this structure can control the magnetization direction of the highly functional magnetic thin film under an electric field, high-performance magnetic devices with low power consumption are easily obtained. The magnetic domain structure of the [Co/Pd] dots fabricated on the (Bi,La)(Fe,Co)O3thin film was analyzed by magnetic force microscopy (MFM). The structure was de-magnetized before the local electric-field application and magnetized after applying the field, showing reduced magnetic contrast of the dot. The line profile of the MFM image revealed a downward magnetic moment of 75%, which reversed to upward under the local electric field. Magnetic interaction between the (Bi,La)(Fe,Co)O3and [Co/Pd] layers was also observed in magnetization hysteresis measurements. These results indicate that the magnetization direction of the [Co/Pd] dots was transferred through the magnetization reversal of the (Bi,La)(Fe,Co)O3layer under a local electric field. That is, the magnetization of [Co/Pd] dots were reversed by applying a local electric field to the multilayer structure. This demonstration can potentially realize high-performance magnetic devices such as large capacity memory with low power consumption.

Short range biaxial strain relief mechanism within epitaxially grown BiFeO3

Lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism is investigated for the BiFeO₃ films grown on La_0.6Sr_0.4MnO₃/SrTiO₃ and YAlO₃ substrates. Nano-beam electron diffraction, structure factor calculation and x-ray reciprocal space mapping unambiguously confirm that the crystal structure within both of the BiFeO₃ thin films is rhombohedral by showing the rhombohedral signature Bragg’s reflections. Further investigation with atomic resolution scanning transmission electron microscopy reveals that while the ~1.0% of the lattice mismatch found in the BiFeO₃ grown on La_0.6Sr_0.4MnO₃/SrTiO₃ is exerted as biaxial in-plane compressive strain with atomistically coherent interface, the ~6.8% of the lattice mismatch found in the BiFeO₃ grown on YAlO₃ is relaxed at the interface by introducing dislocations. The present result demonstrates the importance of: (1) identification of the epitaxial relationship between BFO and its substrate material to quantitatively evaluate the amount of the lattice strain within BFO film and (2) the atomistically coherent BFO/substrate interface for the lattice mismatch to exert the lattice strain.

A simple, one-step hydrothermal approach to durable and robust superparamagnetic, superhydrophobic and electromagnetic wave-absorbing wood

In this work, lamellar MnFe₂O₄ was successfully planted on a wood surface through the association of hydrogen bonds via the one-pot hydrothermal method. Simultaneously, the fluoroalkylsilane (FAS-17) on the surface of the MnFe₂O₄ layer formed long-chain or network macromolecules through a poly-condensation process and provided a lower surface energy on the wood surface. The MnFe₂O₄/wood composite (FMW) presented superior superparamagnetism, superhydrophobicity and electromagnetic wave absorption performance. The results indicated a saturation magnetization of the FMW with excellent superparamagnetism of 28.24 emu·g^-1. The minimum value of reflection loss of the FMW reached -8.29 dB at 16.39 GHz with a thickness of 3 mm. Even after mechanical impact and exposure to corrosive liquids, the FMW still maintained a superior superhydrophobicity performance.

Photocarrier transport and dynamics in mixed-phase BiFeO3 films

We report a remarkable photoinduced relaxation process and its dependence of thickness and temperature in mixed-phase BiFeO₃ films grown on (001) LaAlO₃ substrates. When the films are illuminated by the light above the bandgap, their resistances are reduced with the increase of temperature. The photoinduced change of resistance reaches to the maximum of about 2.17 × 10^5% at 300 K. It is noted that the relaxation processes of the resistance are significantly different between T-like phase and T-R mixed phase due to structural strain, symmetry breaking and built-in electric field at the phase boundaries. These results provide more insights into intrinsic mechanisms of mixed-phase multiferroic materials and potential applications in all-oxide photoelectric devices.