This observation strongly suggests a contribution to the ΔM s due to the presence of P(VDF-HFP) in the form of an enhancement of the saturation magnetization of the composite, with the enhancement stronger for samples with a lower CFO:P(VDF-HFP) ratio. CoFe2O4 nanocrystal powders show less than 1% variation in hysteresis loops, whereas CFO/P(VDF-HFP) films show enhancements
up to 20.7% in ΔM s. The enhancement selleck chemicals of the M s value from the P(VDF-HFP) phase, we believe, is a concerted Selleck Selumetinib effect and is evident of a ME effect, specifically, through inverse magnetorestrictive coupling. First, the magnetostrictive effect induces a distortion of the crystal lattices of CoFe2O4 under an applied magnetic field, which in turn leads to local strains or stresses of between the piezoelectric and magnetic phases via intimate mechanical contact. The hypothesis of the influence of intimate mechanical contact between nanocrystals and P(VDF-HFP) is already supported by the observation Adriamycin research buy of permittivity changes unexplained by volume fraction alone, described above. We postulate that the interfacial stress is inversely applied on the CFO phase, which further leads to the change of domain magnetization as a result of an inverse magnetostrictive effect. The effect is quantified
by Equation 5: (5) where E is the magnetic strain energy density, λ s is the magnetostrictive expansion at saturation, θ is the angle between the saturation magnetization, and σ is the stress applied on a single magnetic
domain . With limited expansion allowed by intimate contact of two hard phases, when compression is applied to CFO phase, the energy is minimized when magnetization is parallel to σ (θ = 0). Consequently, M s is increased by tension. Moreover, in a sample of pure CFO nanoparticles (M s = 66 emu/g) each Co2+ ion exhibits a magnetic moment of 2.7 μB, while in the 10 Cyclin-dependent kinase 3 wt.% CFO/P(VDF-HFP)) films (M s = 8.0 emu/g), the Co2+ ion shows a net magnetic moment of 3 μB, which equals the maximum magnetic moment a Co2+ ion can offer in the inverse spinel structure. This observation indicates that by intimate mechanical coverage of the CFO particles, P(VDF-HFP) reduces the nanocrystals’ degree of surface disorder and surface anisotropy via redistributing charges and dipoles within the copolymer matrix, which allows the magnetization of the cobalt ions to completely follow the external magnetic field. Additionally, as the content of cobalt ferrite nanoparticles increases, the particles’ tendency towards agglomeration increases. The interfacial area is reduced due to the formation of small clusters of nanoparticles, and therefore, the interfacial interaction is weakened. This explains why the M s enhancement is strongest in the 10 wt.% sample (+20.7%), in which the nanoparticles are more completely dispersed, compared to 30 and 50 wt.% samples (+9.6% and +8.6%, respectively).