Phase Transition-Induced Modulation of Exchange Bias in Fe/BiFeO3 Bilayers

Many of researches indicate that epitaxial BiFeO3 (BFO) films deposited on LaAlO3 (LAO) substrate undergo strain-driven phase transition from a tetragonal-like phase (T-BFO) to a rhombohedral-like phase (R-BFO), and a mixed phase (M-BFO) that T-BFO coexists with R-BFO forms in the phase transition process. It is necessary to explore how BFO phase transition affects the exchange bias in ferromagnet (FM)/BFO bilayers. In our studies, aforementioned BFO phase transition is accomplished by varying BFO films thickness. Using 5 nm-thick Fe as ferromagnetic layer deposited on 9–354 nm-thick BFO as antiferromagnetic layer, the exchange bias in Fe/BFO bilayers exhibits that Fe/M-BFO bilayers shows smaller exchange bias than Fe/T-BFO and Fe/R-BFO bilayers. We ascribed the effect of the BFO phase transition on the exchange bias to the domain walls caused by the exchange interaction between T-BFO and R-BFO across their boundaries. Additionally, for the same reason, the coercivity also exhibits the same variation trend as the exchange bias does. Our studies will help to promote the application of controlling the ferromagnetic magnetization by the electric field.

Large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity in DyCrO4

All the magnetoelectric properties of scheelite-type DyCrO4 are characterized by temperature- and field-dependent magnetization, specific heat, permittivity, electric polarization, and neutron diffraction measurements. Upon application of a magnetic field within ±3 T, the nonpolar collinear antiferromagnetic structure leads to a large linear magnetoelectric effect with a considerable coupling coefficient. An applied electric field can induce the converse linear magnetoelectric effect, realizing magnetic field control of ferroelectricity and electric field control of magnetism. Furthermore, a higher magnetic field (>3 T) can cause a metamagnetic transition from the initially collinear antiferromagnetic structure to a canted structure, generating a large ferromagnetic magnetization up to 7.0 μB f.u.−1. Moreover, the new spin structure can break the space inversion symmetry, yielding ferroelectric polarization, which leads to coupling of ferromagnetism and ferroelectricity with a large ferromagnetic component.

Multiferroic Properties of Nanopowder-Synthesized Ferroelectric-Ferromagnetic 0.6BaTiO3-0.4NiFe2O4Ceramic

Multiferroic 0.6BaTiO3-0.4NiFe2O4dense nanoceramic composites were synthesized via a powder-in-sol precursor hybrid chemical synthesis route and a ceramic sintering process. At the measured frequency range (1 kHz~1 MHz), the relative dielectric constant is 150~1670 and the dielectric loss is 0.05~0.70. The composite ceramic showed obvious coexistence of ferroelectric and ferromagnetic phases. With the increase of temperature, the saturation ferromagnetic magnetization decreases, while the ferroelectric polarization increases.

Ferromagnetic Co-P Powders with Nanodiamond and Corundum Precipitates

Powders of Ñî-Ð alloy with ultradispersed corundum (Al2O3) and detonation nanodiamond (DND) precipitates were synthesized by chemical reduction. The products were characterized by X-ray diffraction and scanning electronic microscopy. The shape of the particles was spherical and they were ferromagnetic. Magnetization dependence on field in applied fields of up to 40 kOe and magnetization dependence on temperature in the temperature range from 2 to 300 K were measured. Influence of precipitates on magnetic properties was studied.