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Register a new userGiant Positive Magnetoresistance in Co@CoO Nanoparticle Arrays
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We report the magnetotransport properties of self-assembled Co@CoO nanoparticle arrays at temperatures below 100 K. Resistance shows thermally activated behavior that can be fitted by the general expression of R exp{(T/T0)^v}. Efros-Shklovskii variable range hopping (v=1/2) and simple activation (hard gap, v=1) dominate the high and low temperature region, respectively, with a strongly temperature-dependent transition regime in between. A giant positive magnetoresistance of >1,400% is observed at 10K, which decreases with increasing temperature. The positive MR and most of its features can be explained by the Zeeman splitting of the localized states that suppresses the spin dependent hopping paths in the presence of on-site Coulomb repulsion.
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We report on giant positive magnetoresistance effect observed in VOx thin films, epitaxially grown on SrTiO3 substrate. The MR effect depends strongly on temperature and oxygen content and is anisotropic. At low temperatures its magnitude reaches 70% in a magnetic field of 5 T. Strong electron-electron interactions in the presence of strong disorder may qualitatively explain the results. An alternative explanation, related to a possible magnetic instability, is also discussed.
The radiative heat transfer between gold nanoparticle layers is presented using the coupled dipole method. Gold nanoparticles are modelled as effective electric and magnetic dipoles interacting via electromagnetic fluctuations. The effect of higher-order multipoles is implemented in the expression of electric polarizability to calculate the interactions at short distances. Our findings show that the near-field radiation reduces as the radius of the nanoparticles is increased. Also, the magnetic dipole contribution to the heat exchange becomes more important for larger particles. When one layer is displayed in parallel with respect to the other layer, the near-field heat transfer exhibits oscillatory-like features due to the influence of the individual nanostructures. Further details about the effect of the nanoparticles size are also discussed.
We report here the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to Pm-3m space group. The sample is found to be paramagnetic down to 2 K with metallic character. On application of magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows negative temperature coefficient of resistivity below about 50 K under the application of field gretare than or equal to 80 kOe, signifying a field-induced metal to `insulating transition. The observed magnetoresistance follows Kohlers rule below 20 K indicating the validity of the semiclassical model of electronic transport in metal with a single relaxation time. A multi-band model for electronic transport, originally proposed for semimetals, is found to be appropriate to describe the magneto-transport behavior of the sample.
We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance within the plane transverse to the current flow, of Pt/Co bilayers. We find that the SMR increases with increasing Co thickness: the effective spin Hall angle for bilayers with thick Co exceeds the reported values of Pt when a conventional drift-diffusion model is used. An extended model including spin transport within the Co layer cannot account for the large SMR. To identify its origin, contributions from other sources are studied. For most bilayers, the SMR increases with decreasing temperature and increasing magnetic field, indicating that magnon-related effects in the Co layer play little role. Without the Pt layer, we do not observe the large SMR found for the Pt/Co bilayers with thick Co. Implementing the effect of the so-called interface magnetoresistance and the textured induced anisotropic scattering cannot account for the Co thickness dependent SMR. Since the large SMR is present for W/Co but its magnitude reduces in W/CoFeB, we infer its origin is associated with a particular property of Co.
We report about a combined structural and magnetometric characterization of self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide nanoparticles with a diameter of 20 nm were synthesized by thermal decomposition. The nanoparticle suspension was spin-coated on Si substrates to achieve self-organized arrays of particles and subsequently annealed at various conditions. The samples were characterized by x-ray diffraction, bright and dark field high resolution transmission electron microscopy (HRTEM). The structural analysis is compared to the magnetic behavior investigated by superconducting interference device (SQUID) magnetometry. We can identify either multi-phase FeO/g-Fe2O3 or multi-phase FeO/Fe3O4 nanoparticles. The FeO/g-Fe2O3 system shows a pronounced exchange bias effect which explains the peculiar magnetization data obtained for this system.
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