A. J. Gualdi

Effect of Ferrite Concentration on Dielectric and Magnetoelectric Properties in (1-x)Pb(Mg1/3Nb2/3)0.68Ti0.32O3 +(x) CoFe2O4 Particulate Composites

In this work the effect of ferrite concentration on dielectric and magnetoelectric properties in (1-x)Pb(Mg1/3Nb2/3)0.68Ti0.32O3 +(x) CoFe2O4, 0.10 ≤ x ≤ 0.50, particulate composites sintered by conventional method was investigated. Optimized sintering conditions, which resulted in samples with relatively high density and resistivity values, allowed an effective poling processing. Moreover, resulting low phase interdiffusion guaranteed a good 0-3 connectivity maintenance for all compositions. Such sample features allowed to verify that the magnetoelectric coefficient increases as a function of the ferrite content as theoretically expected, reaching a maximum of 30 mV/cmOe for 50 molar% of ferrite phase).

Stress magnetization model for magnetostriction in multiferroic composite

An alternative to obtain multiferroic materials is the production of composite materials that combine ferroelectric and magnetic materials. In particular, the use of magnetostrictive materials as ferromagnetic phase in composites is very important because the mechanical stress applied in ferroelectric phase induces the appearance of magnetoelectric effect. In this work, we have proposed a generalized model for the magnetostriction dependence with the magnetization of the 0-3 type composite magnetoelectric materials. Including both piezomagnetic and stress dependence in the magnetostriction, a relevant improvement was reached as compared to the ordinary square magnetization model. Based on the Gibbs free energy expansion, the magnetostriction behavior of the composite (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3/CoFe2O4 at 300 K and 5 K is described. Furthermore, using the piezomagnetic correction, the magnetostriction data for the pure CoFe2O4 is fitted showing that this ferrite presents a relevant piezomagnetic effect.

Angular Dependence of the Magnetoelectric Effect on PMN-PT/CFO Particulate Composites

In this work the angular dependence of the magnetoelectric response in PMN-PT/CFO particulate magnetoelectric composites was investigated. Magnetostrictive and magnetoelectric measurements were performed as a function of the angle between electric polarization and magnetic bias field for 0–3 particulate ceramic composites prepared through solid state reaction and hot uniaxial pressing methods. The magnetoelectric response showed a strong angular dependence, which can be directly related to the magnetostrictive and piezoelectric properties of composites.

Understanding the dynamic magnetization process for the magnetoelectric effect in multiferroic composites

Based on a magnetic relaxation model, an approach that includes the spin dynamics is proposed and applied to describe the magnetoelectric (ME) effect frequency dependence for a 0–3 type composite at low temperatures. Our results show that the ME coefficient, in low temperatures, for PMN-PT/CFO ( (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3/CoFe2O4) composite has a step-like behavior on the hysteresis loop for frequency of 1 kHz, contrasting with the results at low frequencies (10 Hz). This approach assumes that the ferromagnetic and ferroelectric phases are coupled through the interactions of the spins of the ferromagnetic phase with the composite phonons by spin/lattice relaxation.

Relationship between the ferromagnetic phase and the magnetoelectric coupling in hot pressed Pb(Mg1/3Nb2/3)O3-PbTiO3 based particulate composites

ABSTRACT The influence of ferromagnetic phase properties on the magnetoelectric response of hot pressed particulate composites formed by 80 mol% of 0.675[Pb(Mg1/3Nb2/3)O3]–0.325[PbTiO3] as piezoelectric matrix and 20 mol% of NiFe2O4, CoFe2O4 or BaFe12O19 phases was analyzed. The hot pressing sintering method was suitable for obtaining composites with apparent density higher than 94% and electric resistivity close to 109 Ω.m, independently of the ferromagnetic phases used. The magnitude of the magnetoelectric coupling seems to be governed by the piezoelectric properties of ferroelectric PMN-PT matrix, and the zero bias magnetoelectric coefficient values are determined by the ferromagnetic hardness of the magnetic phase.

Effect of different ferroelectric phases on magnetoelectric properties of Co-ferrite particulate composites

ABSTRACT In this work, the influence of the ferroelectric phase on the magnetoelectric response of particulate magnetoelectric composites were investigated. The composites constituted by PMN-PT, PZT and PBN as ferroelectric phase and CoFe2O4 as ferromagnetic phase (prepared through the conventional solid state method) were synthesized by hot forging method in the 80/20 molar ratio using the 0-3 connectivity. We show that the increase in the magnetic coercive field for composites composed by PZT and PBN in comparison to the PMN–PT ferroelectric phase is related to the different elastic constants of ferroelectric matrix used. Also, the ME properties has been attributed to the mechanically mediated effect, in which the ME values are strongly dependent to the piezoelectric and elastic properties of the ferroelectric phases and the maximization of ME coefficient was obtained using ferroelectric and ferromagnetic phases with similar elastic modulus.

Magnetodielectric properties of (1−x)PMN-PT/xCFO particulate composites

The magnetic field dependence of the magnetodielectric effect of (1-x)PMN-PT/xCFO particulate composites was systematically investigated. At room temperature, it was found there is a giant magnetodielectric response up to 10% around the electromechanical resonance frequency for a magnetic field of 15kOe. Additionally, at low magnetic fields a positive magnetodielectric coefficient (~2%) associated to the magnetoelectric coupling polarization and dependent of the CFO concentration was observed.

Ferroic properties of 0.675[Pb(Mg1/3Nb2/3)O3]−0.325[PbTiO3]/CoFe2O4 prepared by spark plasma sintering

ABSTRACT This paper reports the electric, magnetic and magnetoelectric properties of particulate composites of the system with ferroelectric phase 0.675[Pb(Mg1/3Nb2/3)O3]−0.325[PbTiO3] and magnetic phase CoFe2O4 prepared by Spark Plasma Sintering technique. Optimized sintering and thermal annealing parameters were applied in order to achieve highly dense microstructure with sub micrometric grain size distribution for both phases. The results from the dielectric measurements showed a diffuse and dispersive phase transition. P-E and M-H loops revealed the simultaneous existence of ferroelectric and ferrimagnetic ordering, respectively. Moreover, at cryogenic temperatures an anomalous behavior on the bias magnetic field dependence was observed for the magnetoelectric voltage coefficient.