Lihua Yin

Multiferroic and magnetoelectric properties of Bi1−xBaxFe1−xMnxO3 system

Multiferroic compounds Bi1−xBaxFe1−xMnxO3 (0.2 ≤ x ≤ 0.5) have been synthesized by conventional solid-state reaction. X-ray diffraction shows that Bi1−xBaxFe1−xMnxO3 is single phase up to x = 0.4. These samples exhibit magnetism and ferroelectricity simultaneously at room temperature. A considerable enhancement of the polarization on magnetic poling and a dielectric anomaly near the magnetic transition (TC) due to the intrinsic magnetoelectric coupling effect are observed in the Bi0.8Ba0.2Fe0.8Mn0.2O3 sample. The dielectric constant for the Bi0.8Ba0.2Fe0.8Mn0.2O3 sample at room temperature decreases with increasing applied magnetic fields, and the coupling coefficient (e(H) − e(0))/e(0) reaches −0.2% at H = 6 kOe.

Magnetic and dielectric properties of Aurivillius phase Bi4.2Nd0.8Ti3Fe0.5Co0.5O15

The magnetic and dielectric properties of Bi4.2Nd0.8Ti3Fe0.5Co0.5O15 are investigated by using the measurements of magnetization and dielectric constant. The sample is ferromagnetic with the Curie temperature of 428u2009K. And the remnant magnetization Mr is 0.5u2009emu/g, which is two orders of magnitude higher than Mr of Bi5Ti3Fe0.5Co0.5O15. The ferromagnetism in Bi4.2Nd0.8Ti3Fe0.5Co0.5O15 can be ascribed to spin canting of the Fe-based and Co-based sublattices via Dzyaloshinskii-Moriya interaction. Both the dielectric constant and dielectric loss have the characteristics of relaxation, and the activation energy turns out to be 0.658±0.013u2009eV.

Magnetic-polaron?induced colossal magnetocapacitance in CdCr2S4

The origin of colossal magnetoresistance and colossal magnetocapacitance in a CdCr2S4 system was investigated. Thermoelectric-power and electronic spin resonance spectra reveal that the magnetic polaron is responsible for the colossal magnetoresistance in the n-type sample. The existence of magnetic polarons in the paramagnetic insulting matrix forms an intrinsic Maxwell-Wagner system, leading to the appearance of colossal magnetocapacitance. Being consistent with the evolution of magnetic polarons upon cooling, the Maxwell-Wagner system is valid around insulator-metal transition, where the resistance derived from impedance spectroscopy matches perfectly with DC resistance.

The effects of quenching on electrical properties, and leakage behaviors of 0.67BiFeO 3 –0.33BaTiO 3 solid solutions

Ferroelectric solid solutions of 0.67BiFeO3–0.33BaTiO3 were prepared by a Pechini method followed by quenching process. The XRD results indicate that both the furnace-cooled and water-quenched samples are consist of rhombohedral and tetragonal phases. SEM images show that the quenching process does not change the microstructure of 0.67BiFeO3–0.33BaTiO3 solid solutions. The quenched sample exhibits well-defined P–E hysteresis loop with remnant polarization of 23 µC/cm2 at room temperature. The leakage mechanism of the furnace-cooled sample is Ohmic conduction mechanism, whereas the leakage mechanism of water-quenched sample is predominated by field-assisted ionic conduction at room-temperature and 50xa0°C and then changes to three different conduction mechanisms at 100xa0°C.