N. Zhang

Converse magnetoelectric effects on heterotype electrostrain-piezopermeability composites

By using the product effect of electrostrain and piezopermeability, a heterotype composite consisting of a bar of Pb(Zr,Ti)O3 and a ring of MnZn ferrite with higher permeability has been developed, and its converse magnetoelectric effect has been investigated. Under a constant electric field of 5 kV/cm, about 20% electric-field-induced changes in permeability and impedance have been observed with the composite device over a wide frequency band. The electric-field dependence of the permeability and impedance shows a ferroelectric relaxation behavior. This composite is a candidate material for electrically controlled magnetic devices.

Giant positive magnetoresistance in composite (La0.83Sr0.17MnO3)0.6(ITO)0.4

We have studied the transport property of the composites (La0.83Sr0.17MnO3)1−x indium tin oxide (ITO)x [ITO=(In2O3)0.95(SnO2)0.05], which were fabricated by mechanically mixing La0.83Sr0.17MnO3 and ITO grains. A giant positive magnetoresistance (PMR) has been observed above the Curie temperature Tc for the samples with x around 0.40 besides the negative magnetoresistance near and below the Tc. The magnetoresistive ratio for the PMR can reach 39.3% under a magnetic field μ0H=2800Oe for (La0.83Sr0.17MnO3)0.6(ITO)0.4. Analysis suggests that the magnetic field-induced broadening of the p-n barrier between both kinds of grains and a suitable density of the p-n heterostructures should be responsible for the PMR behavior.

Capacitive type magnetoimpedance effect in piezoelectric-magnetostrictive composite resonator

In this article, a significant capacitive type magnetoimpedance effect of piezoelectric-magnetostrictive (PM) composite resonator is presented at room temperature. The variations of relatively effective permittivity of the PM resonator with a dc magnetic field are responsible for the capacitive type magnetoimpedance effect. About 225% and 50% of magnetoimpedance have been achieved at anti-resonance and resonance frequencies of the PM resonator, respectively, which reveals a stronger magnetoelectric coupling at the anti-resonance frequency than that at the resonance frequency of the PM resonator. A detailed analysis also indicates that the magnetocapacitance and magnetoinduction effects of the resonator were originated from the variations of relatively effective permittivity of the resonator. More than 200% and 170% of magnetocapacitance and magnetoinduction were achieved at room temperature in the anti-resonance window, respectively, and also about 150% and 60% of capacitance and induction modulation were observed in the resonance window by applying the dc magnetic fields. The capacitive type magnetoimpedance effect is expected to be used in the design of magnetic-field-tuned ultrasonic transducer.

Electrostrain-controlled displacement-permeability in composite of ferroelectrics and heterotypic complex ferrite

By using the product effects of electrostrain and displacement-permeability, a composite containing a bar of Pb(Zr,Ti)O3 and two I-shaped ferrites were developed, and its electromagnetic effect was investigated. Under a constant electric field of 5 kV/cm, about 36% of the electric field-controlled permeability and impedance were observed in a considerably wide scope of frequency. The electric-field dependent inductance and impedance of the composite device showed a ferroelectric relaxation behavior. Analysis showed that the degenerating field-dependent permeability was responsible for the electromagnetic effects observed.

The Effect of Magnetic Field-Tuned Resonance on the Capacitance of Laminate Composites

The magneto-electric coupling and magneto-capacitance effect of a layer composite ferromagnet/ piezoelectric/ferromagnet was investigated. Several resonant peaks were observed on the curves of the capacitance versus frequency. The resonant peaks were found to shift under an applied magnetic field, and the impedance of the sample can be changed from capacitive to inductive ones with changing the field. Thus, giant negative and positive magneto-capacitance effects can be observed simultaneously under a magnetic field less than 1 k Oe near the resonant points. Experimental and theoretical analysis showed that such magnetically tuned variation in impedance originates from the magnetic field-induced change of the compliances of the magnetic phase of the composite.

Magneto-Birefringence in Layered Composites at Room-Temperature

By the product of magnetostriction and stress-birefringence, the laminate composites that can show Voigt effect was suggested and fabricated. Under a magnetic field no stronger than 1900 Oe, a phase difference of about 3.3 was observed for a trilayer composite Tb1-xDyxFe2-y / polycarbonate / Tb1-xDyxFe2-y with the polycarbonate layer in size of 5×2.75×20 mm3 at room temperature, resulting in a half-wave magnetic field of no greater than 270 Oe.