R. J. Gambino

The effect of organo clay and adsorbed FeO3 nanoparticles on cells cultured on Ethylene Vinyl Acetate substrates and fibers

Nanocomposites of Ethylene Vinyl Acetate (EVA 260) with Cloisite 20A organo clay and Cloisite 20A organo clay impregnated with Fe(CO)(5) were produced in a twin-screw extruder. Dynamic mechanical analysis (DMA) measurements indicated that the moduli increased monotonically for the Cloisite, up to a concentration of 10%, after which the modulus decreased. Adult human dermal fibroblasts (AHDF) were plated on these surfaces and the cell growth was found to be maximal on the nanocomposites containing 10% Cloisite. AHDFs cultured on substrates with higher Cloisite content had low surface area, poor growth curves, and misshaped actin fibers. Compounding EVA with Fe(CO)(5) soaked Cloisite did not enhance the modulus even at a loading of 10%. TEM images indicate nanoparticles form and coat the Cloisite platelet surfaces, possibly interfering with the exfoliation process. On the other hand, cell culture of MC3T3 osteoblasts proliferated on the Fe containing nanocomposites, the largest effect being observed when cultured in a constant magnetic field. These results indicate how the chemical nature of the Cloisite 20A organo clay can also play a major role. Finally, since natural ECM is fibrillar, these EVA nanocomposites were also electrospun into micron thick fibers. MC3T3s proliferated well on these fibers and the MC3T3 proliferation was maximized by culture on electrospun aligned fibers in a constant magnetic field.

Structural and magnetic characterization of ion-beam deposited Nife/NixFe1-xO composite films

Nanocomposite films of Ni80Fe20/NixFe1−xO were prepared by a dual ion-beam deposition technique. The structural and magnetic properties of nanocomposite films fabricated with oxygen content in the deposition assist beam ranging from 0% to 55% were studied. The dependence of the resistivity on oxygen percent shows that the compositions with exchange-enhanced coercivity are close to a percolation threshold. A strong temperature dependence of coercivity Hc and exchange bias field Hex is found in these composite films. Films prepared with 46% O2 in the assist beam exhibit an enhanced Hc relative to Permalloy (Ni80Fe20) and a characteristic shifted hysteresis loop indicative of exchange coupling between the constituent metal and oxide phases. At T=10u2009K, films prepared with 44% O2 in the assist beam have an exchange shift Hex∼−225u2009Oe with a blocking temperature TB∼100u2009K that reflects the low Neel temperatures of FeO-rich NixFe1−xO solid solutions.

Neutron diffraction and ferromagnetic resonance studies on plasma-sprayed MnZn ferrite films

The magnetic properties of MnZn ferrites are affected by the plasma spray process. It is found that improvements can be made by annealing the ferrite films at 500°C–800°C. The annealing induced magnetic property changes are studied by neutron diffraction and ferromagnetic resonance techniques. The increase of the saturation magnetization is attributed to the cation ordering within the spinel lattice, which increases the magnetic moment per ferrite formula. The refinements on the neutron diffraction data suggest that the redistribution of the cation during annealing neither starts from a fully disordered state nor ends to a fully ordered state. The decrease of the coercivity is analyzed with the domain wall pinning model. The measurements on the magnetostriction and residual stress indicate that coercive mechanisms arising from the magnetoelastic energy term are not dominant in these ferrite films. The decrease of the coercivity for annealed ferrite films is mainly attributed to the decrease of the effecti...

Anisotropic electrical conduction from heterogeneous oxidation states in plasma sprayed TiO2 coatings

Microstructural and electrical characterizations of air plasma sprayed TiO2 coatings were carried out to investigate the details of deoxidation during the spray process and the changes following air annealing. The coatings were found to behave as an n-type semiconductor indicating the presence of oxygen vacancies. Direct-current resistivity measurements in plane (ρIP) and through thickness (ρTT) of the coatings as a function of annealing time and temperature showed remarkably large anisotropies (=ρTT∕ρIP) of up to 105. Impedance spectroscopy of the specimens coupled with microstructural analysis revealed that the origin of this anisotropy lies in the heterogeneous deoxidation and reoxidation behavior of the coatings. Due to rapid quenching, the high temperature deoxidation state is preserved in the splat boundaries making them more conductive than the bulk of the splat in the as-sprayed coating. Upon annealing in air, the splat boundaries get selectively oxidized due to faster surface diffusion of oxygen ...

Composition dependence of the Hall effect in amorphous TbxCo1−x thin films

The Hall effect in amorphous TbxCo1−x thin films has been studied quantitatively with respect to Tb at.u200a% in films. Amorphous TbxCo1−x thin films exhibit unusually large spontaneous Hall coefficients (Rs≈2×10−9u200aΩu200acm/G, whose sign is strongly dependent on the film composition as governed by the relation ρH=Rs4πMS. At Tb compositions below the compensation composition xcomp, the Hall resistivity ρH is positive and the sign is reversed for Tb compositions above xcomp. Even though the saturation magnetization at x>xcomp is lower than at x<xcomp, the absolute Hall resistivity |ρH| and Hall coefficient |Rs| are higher. As the Tb content increases in the films, the resistivity increases. In amorphous TbxCo1−x thin films, the Hall angle |ρH/ρ| is sensitive to the resistivity of the films. On the basis of electrical resistivities, Hall resistivities, and Hall angles in amorphous TbxCo1−x films, the side jump Δy of 0.16 to 0.26 A was calculated.

Microscopic Magnetic Characterization Of Submicron Cobalt Islands Prepared Using Self Assembled Polymer Masking Technique

Patterns of submicron cobalt islands were created on silicon by using self-assembled co-polymers as etching masks. The synthesis conditions were varied to create specific magnetic island morphologies. The magnetic structure and magnetization reversal of interconnected, as well as interacting and non-interacting islands were systematically studied using magnetic force microscopy. Differences in magnetic characteristics were observed and correlated with the thin film morphologies. The result of these studies include the transition from single to multidomain configuration as a function of island size, domain boundary characteristics near coercivity, evidence of magnetization rotation with increasing reverse magnetic field, and evidence of collective switching behavior in interacting single domain islands.

Exchange bias in a thin film dispersion of MnO nanocrystallites in Co

Unusually large magnetization loops shifts along the field axis, of the same order as those observed in the archetypical exchange biased system Co/CoO, have been measured in a Co/MnO thin film made using reactive ion beam assisted deposition. These large loop shifts are unexpected for a system with an antiferromagnetic anisotropy that is two orders of magnitude less than that of CoO. This magnetic behavior is attributed to the nanoscale nature of the crystallites that constitute the film, where the surface area to volume ratio is large enough so that a sizable surface magnetic contribution provides the necessary antiferromagnet to ferromagnet coupling for the large measured exchange bias.

Spontaneous Hall effect in amorphous Tb–Fe and Sm–Fe thin films

The spontaneous Hall effect in amorphous Tb–Fe and Sm–Fe thin films, which possess excellent magnetic softness, is investigated to seek a possibility of practical applications of these thin films. The resistivity of Tb–Fe thin films ranges from 180 to 250 μΩu200acm as the Tb content varies from 35 to 46 at.u200a%. Tb–Fe thin films show negative Hall resistivity ranging from −7.3 to −5.0 μΩu200acm in the same composition range, giving the normalized resistivity ratio from −4.1% to −2.0%. On the other hand, the resistivity of Sm–Fe thin films ranges from 150 to 166 μΩu200acm as the Sm content varies from 22 to 31 at.u200a%. Sm–Fe thin films show positive Hall resistivity which varies from 7.1 to 2.8 μΩu200acm in the same composition range, giving the normalized resistivity ratio from 4.8% to 1.7%. Between the two different sets of samples, Tb–Fe thin films with perpendicular anisotropy are considered to be more suitable for practical applications, since saturation is reached at a low magnetic field.

Magneto‐optic properties and exchange interaction of the macroscopic ferrimagnet Co1−x−yTbx(EuS)y

Polar Kerr‐rotation spectra and hysteresis loops have been measured in Co1−x−yTbx(EuS)y, with 0≤x≤0.21 and 0≤y≤0.21, and compared to the macroscopic ferrimagnet Co1−y(EuS)y and to amorphous Co1−xTbx. The measurements were taken at room temperature and at 7 K over a wide photon energy range of 1.1–4.6 eV in fields up to 2.77 T. The addition of Tb retains the phase‐separated nature yielding a material consisting of a Co–Tb matrix containing crystalline EuS precipitate particles with about 2 nm diameter. Up to 8% Tb is substituted for Eu in the EuS phase. The Kerr rotations are rather small reaching −0.25° at room temperature and increasing to −0.85° at 7 K, i.e., no optical enhancement is observed as in Co(EuS). This is most likely due to the much smaller size of the EuS crystallites. An ‘‘s’’‐shaped feature in the Kerr‐rotation spectra can be assigned to an Eu2+ 4f→5d transition while a contribution from the Tb3+‐4f states shows up as a decrease with increasing photon energies. At 7 K, the Tb and Eu magnet...

Magnetic exchange effects in a nanocomposite Ni/NiO film

The unique sample preparation technique of reactive ion beam assisted deposition has been used to make a thin film sample of interdispersed Ni and NiO nanocrystallites. The ferromagnetic and antiferromagnetic crystallites in the film provide a unique geometry that lies between that of bulk exchange biased systems and layered thin films, and provides clear evidence of exchange effects. Interphase magnetic exchange is demonstrated by suppression of the Neel and Curie temperatures of the components, as well as by the typical hysteresis loop shift that is a measure of the exchange field strength. Furthermore, a strong temperature and maximum applied field dependence for both the coercivity and exchange field strength is present, indicating competition between the exchange interaction of the Ni and NiO nanocrystallites and the external field and NiO surface magnetic coupling interactions.