Optimized Magnetodielectric Coupling on High-Temperature Polymer-Based Nanocomposites

Abstract

CoFe2O4 (CFO) ferrite nanoparticles with an average size of 15 nm were synthesized by a hydrothermal method and used to develop magnetodielectric (MD) composites with the piezoelectric diamine 2CN/diamine 0CN as polymer matrix . It is shown that the dielectric constant, dielectric loss, and saturation magnetization values of the composites increase with the increasing CFO content, being 4.4, 0.01, and 12 emu.g -1 , respectively, for the sample with 20 weight percentage (wt.%) of ferrite. Additionally the large MD response (MD (%)=10.15 and magnetodielectric coefficient (γ)=5.8x10 -2 ) demonstrates the effective magneto-mechano-electrical interaction between magnetostrictive CFO and the polymer matrix. Such high MD response, the highest reported for polymer-based composite materials, can support innovative applications in the areas of sensors, actuators, and filters, among others.

Investigation of Direct and Indirect Magnetoelectric Couplings in P(VDF-HFP)/CoFe2O4 Nanofiber Composite Films

“…In addition, the Landau free-energy expression can also be used to calculate the higher-order ME coupling coefficient (γ) using the following relation: Δε ∼ γ M 2 , i.e., the change in dielectric constant is proportional to the square of the magnetic order parameter and the sign of Δε depends on the sign of γ. Figure shows the relative dielectric constant difference (Δε/ε(0)) as a function of M 2 for unpoled and poled P­(VDF-HFP)/CoFe 2 O 4 composite films.…”

“…By the application of magnetic field, the ferromagnetic phase exhibits a magnetostriction effect and produces strain in the film. The strain, in turn, induces a piezoelectric effect in the ferroelectric phase, which creates electric dipoles that change the capacitance of the composite films. , Moreover, the existence of biquadratic coupling in the films reveals that they cannot be used in switchable memory device applications because the coupling term is proportional to the square of the order parameters (i.e., P 2 M 2 ), which cannot make any change in energy by inverting the sign of either P or M.…”

“…The maximum values of MD%, MC%, ML%, and MZ% are summarized in Table . From the table, it is observed that these values decrease with the loading of CoFe 2 O 4 nanofibers, which is attributed to the decrease in the magnetostriction effect . A decrease in the values of MC%, MD%, and ML% and an increase in MZ% are noticed from Table as the results of poling effect.…”

“…The reason for decreases of γ can be stated as follows: the strain is introduced in the films through the magnetostriction effect with the addition of CoFe 2 O 4 nanofibers in the P(VDF-HFP) matrix, and this effect decreases with the higher loading of CoFe 2 O 4 fibers due to the increase in dielectric loss and increase in filler−filler interactions. A similar kind of behavior has been already reported in other CoFe 2 O 4 -based composite films such as OCN 2 CN/CoFe 2 O 4 37 and PVDF/CoFe 2 O 4 . 41,4241,42 Furthermore, γ of poled films is higher than that of unpoled films, and this indicates that the ME coupling of the films is enhanced due to the strain induced by the alignment of electric dipoles in electrical poling conditions.…”

Insights into the optical, magnetic and dielectric properties of some novel polysulfone/NiFe2O4 composite materials

“…The physical properties of synthesized polymer nanocomposites depend essentially on some parameters such as grain size, preparation method and the degree of dispersion of the particles in the polymer matrix . In recent years, various synthetic polymers, such as poly(vinylydene fluoride), aromatic polyimide, polysulfone (PSU) and others, have been used to develop composite materials with improved dielectric and magnetic properties. These polymers present a number of advantageous properties such as high chemical resistance, good thermal stability, superior mechanical properties, biocompatibility, electroactive properties (piezoelectric, pyroelectric and ferroelectric activities) and low surface energy.…”