As a result of the piezoelectric effect, the spatial charges and electric dipoles within the copolymer matrix are redistributed, manifested as variation of effective permittivities from the Kerner model. With higher ferrite contents, the interfacial elastic effect is stronger and leads to a more pronounced departure from the theoretical value. Magnetic
measurements of the CoFe2O4 check details nanocrystals were conducted in both ZFC/FC, and hysteresis modes were analyzed. Figure 5a shows the low field (100 Oe) AG-881 magnetization dependence with temperature (1.84 to 400 K) in ZFC/FC modes. After a ZFC process, the magnetization of the ferrite nanoparticles increases with rising temperature. Unlike other transition metal ferrite nanoparticles (e.g., Fe3O4, NiFe2O4, and MnFe2O4), no maximum magnetization is detected in the ZFC process, indicating that the blocking temperature (T b) of CoFe2O4 nanoparticles is above 400 K, which is consistent with PRIMA-1MET order reported data of T b(CoFe2O4) = 525 K . Additionally, an irreversible magnetic behavior is indicated by the splitting between the ZFC and FC curves. The irreversibility arises from the competition between the energy required for magnetic moment reorientation against the energy barrier associated with magnetoelectricity and the crystalline anisotropy. The field-dependent magnetization at ambient temperature
(Figure 5b) shows a hysteresis with coercivity of 400 Oe, suggesting typical ferrimagnetic behavior. The coercivity represents the strength of the field that is needed to surpass the anisotropy barrier. The saturation magnetization
(M s) and remnant Baf-A1 nmr magnetization (M r) is 66 and 10 emu/g, respectively, comparable with CoFe2O4 nanocrystals obtained by other approaches with similar sizes . The M s value of 66 emu/g is equivalent to magnetic moment dipole of 21.6 μ B per cubic cobalt ferrite unit cell, which is 2.7 μB from each Co2+ ion. Generally Co2+ ions can offer three net spin magnetic moments. The lower value of magnetic moment and subsequent saturation magnetization of these CFO nanoparticles typically originates in the high surface area and concurrent surface disorder. At room temperature, the magnetic anisotropy prevents the magnetization direction of the nanocrystals to completely follow the direction of the external magnetic field. Figure 5 Zero field-cooled and field-cooled (ZFC/FC) and room temperature magnetization curves (a) and hysteresis loop (b). Measured for pure CoFe2O4 nanoparticles. Inset, central region on an expanded scale. M(H) hysteresis loops of the CoFe2O4/P(VDF-HFP) and CFO/PVP nanocomposite thin films were recorded under an applied magnetic field up to 50 kOe. Figure 6a shows hysteresis loops of the 30 wt.% CoFe2O4/PVDF-HFP thin films at various temperatures, indicating typical ferri/ferromagnetic behavior. At 1.9 K, the 30 wt.