We investigated the effect of gadolinium doping (1-5 at.%) on the magnetic and dielectric properties of Fe 3 O 4 nanoparticles, synthesized by the chemical co-precipitation technique, primarily to understand the onset of multifunctional properties such as ferroelectricity and magnetodielectric coupling. The substitution of larger Gd 3+ ions at smaller Fe 3+ octahedral sites in inverse spinel Fe 3 O 4 has significantly influenced the morphology, average crystallite size, and more importantly, the magneto-crystalline anisotropy and saturation magnetization. The magnetocrystalline anisotropy and the saturation magnetization decreases substantially, however, significant increase in the average crystallite size is observed upon Gd doping. Furthermore, temperature-dependent dielectric studies suggest that these nanoparticle systems exhibit relaxor ferroelectric behavior, with much pronounced ferroelectric polarization moment recorded for 5 at.% Gd doped Fe 3 O 4 as compared to its undoped counterpart. K E Y W O R D Sferrites, ferroelectricity/ferroelectric materials, ferromagnetism/ferromagnetic materials, magnetoelectrics Suvra S. Laha and Ehab Abdelhamid contributed equally for this work.

Flexible and self-standing polyvinylidene fluoride (PVDF) films loaded with nanofillers, reduced graphene oxide (RGO), zinc oxide (ZnO) and magnetic iron oxide (Fe3O4) nanoparticles, were prepared by a solvent casting method.

A facile surface hydroxylation treatment to modify the surface of nickel nanoparticles dispersed in ferroelectric polyvinylidene fluoride (PVDF) is reported. A remarkable increase in the amount of polar β phase of PVDF has been observed upon dispersion of nickel nanoparticles in the PVDF matrix. The leakage current reduces drastically in the composite with surface-modified nickel nanoparticles. This improvement has been observed with concurrent enhancement of electrical polarization in the surfacemodified nickel−PVDF composite. However, the magnetic moment of the modified composite is found to be slightly lower than that of the unmodified composite. Most importantly, the composite with surface-modified nickel exhibits magnetodielectric coupling significantly higher than that of the unmodified composite. The magnetodielectric coupling appears to be facilitated by surface hydroxyl groups on nickel. These results establish the potential of facile surface functionlization of nanoparticles toward the design of nanocomposites with higher magnetoelectric coupling.

Flexible inorganic-organic magneto-electric (ME) nanocomposite films (PVDF, PVDF-GO, PVDF-Fe3O4 and PVDF-GO-Fe3O4), composed of well-dispersed graphene oxide (GO 5 wt%) and magnetic Fe3O4 nanoparticles (5 wt%) embedded into a poly(vinylidene-fluoride) (PVDF) matrix, have been prepared by a solvent casting route. The magnetic, ferroelectric, dielectric, magneto-dielectric (MD) coupling and structural properties of these films have been systematically investigated. Magnetic (Ms = 2.21 emu g(-1)) and ferroelectric (P = 0.065 μC cm(-2)) composite films of PVDF-GO-Fe3O4 (PVDF loaded with 5% GO and 5% Fe3O4) with an MD coupling of 0.02% at room temperature (RT) showed a three times higher dielectric constant than that of the pure PVDF film, with a dielectric loss as low as 0.6. However, the PVDF-Fe3O4 film, which exhibited improved magnetic (Ms = 2.5 emu g(-1)) and MD coupling (0.04%) properties at RT with a lower dielectric loss (0.3), exhibited decreased ferroelectric properties (P = 0.06 μC cm(-2)) and dielectric constant compared to the PVDF-GO-Fe3O4 film. MD coupling measurements carried out as a function of temperature on the multi-functional PVDF-GO-Fe3O4 film showed a systematic increase in MD values up to 100 K and a decrease thereafter. The observed magnetic, ferroelectric, dielectric, MD coupling and structural properties of the nanocomposite films are attributed to the homogeneous dispersion and good alignment of Fe3O4 nanoparticles and GO in the PVDF matrix along with a partial conversion of nonpolar α-phase PVDF to polar β-phase. The above multi-functionality of the composite films of PVDF-Fe3O4 and PVDF-GO-Fe3O4 paves the way for their application in smart multiferroic devices.