Characterization of amorphous and nanocrystalline carbon films

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

The surface science of graphene: Metal interfaces, CVD synthesis, nanoribbons, chemical modifications, and defects

Defects are usually seen as imperfections in materials that could significantly degrade their performance. However, at the nanoscale, defects could be extremely useful since they could be exploited to generate novel, innovative and useful materials and devices. Graphene and graphene nanoribbons are no exception. This review therefore tries to categorize defects, emphasize their importance, introduce the common routes to study and identify them and to propose new ways to construct novel devices based on 'defective' graphene-like materials. In particular, we will discuss defects in graphene-like systems including (a) structural (sp(2)-like) defects, (b) topological (sp(2)-like) defects, (c) doping or functionalization (sp(2)- and sp(3)-like) defects and (d) vacancies/edge type defects (non-sp(2)-like). It will be demonstrated that defects play a key role in graphene physicochemical properties and could even be critical to generate biocompatible materials. There are numerous challenges in this emerging field, and we intend to provide a stimulating account which could trigger new science and technological developments based on defective graphene-like materials that could be introduced into other atomic layered materials, such as BN, MoS(2) and WS(2), not discussed in this review.

https://iopscience.iop.org/article/10.1088/0034-4885/75/6/062501/pdf

The role of defects and doping in 2D graphene sheets and 1D nanoribbons

Heteroatom-doped graphene materials have been intensely studied as active electrodes in energy storage devices. Here, we demonstrate that boron-doped porous graphene can be prepared in ambient air using a facile laser induction process from boric acid containing polyimide sheets. At the same time, active electrodes can be patterned for flexible microsupercapacitors. As a result of boron doping, the highest areal capacitance of as-prepared devices reaches 16.5 mF/cm2, 3 times higher than nondoped devices, with concomitant energy density increases of 5–10 times at various power densities. The superb cyclability and mechanical flexibility of the device are well-maintained, showing great potential for future microelectronics made from this boron-doped laser-induced graphene material.

Flexible Boron-Doped Laser-Induced Graphene Microsupercapacitors.

A systematic investigation of lanthanum-based manganite, La0.67Ca0.33MnO3, has been undertaken with a view to understand the influence of varying crystallite size, in the nanoscale, on various physical properties. The materials were prepared by the sol–gel route by sintering at four different temperatures starting from 800 to 1100 °C, with an interval of 100 °C. After the usual characterization of these materials structurally by XRD, their metal-insulator transition (TP) as well as magnetic transition (TC) temperatures were determined. Surprisingly these materials are found to exhibit two different types of behaviors, viz, while TC is found to decrease from 253 to 219 K, TP is increasing from 145 to 195 K with increasing sintering temperature. A systematic study of electrical conductivity of all four materials was undertaken not only as a function of temperature (80–300 K), but also as a function of magnetic field up to 7 T mainly to understand the detailed conduction mechanism in these materials. On analyzing the data by using several theoretical models, it has been concluded that the metallic (ferromagnetic) part of the resistivity (ρ) (below TP) fits well with the equation ρ ( T ) = ρ 0 + ρ 2.5 T 2.5 , indicating the importance of grain/domain boundary effects (ρ0) and electron–magnon scattering processes (∼T2.5). On the other hand, in the high temperature (T>TP) paramagnetic insulating regime, the adiabatic small polaron and VRH models fit well in different temperature regions, thereby indicating that polaron hopping might be responsible for the conduction mechanism.

Effect of sintering temperature on electrical transport properties of La0.67Ca0.33MnO3

Highly textured, as-deposited $La_{0.6}Pb_{0.4}MnO_3$ thin films have been grown on $LaAlO_3$ by pulsed laser deposition. The films are ferromagnetic metals below 300 K. Giant negative magnetoresistance of over 40% is observed at 300 K at 6 T.

Ferromagnetic La0.6Pb0.4MnO3 thin films with giant magnetoresistance at 300 K

Here we report on the magnetic properties of iron carbide nanoparticles embedded in a carbon matrix. The granular distribution of nanoparticles in an inert matrix, of potential use in various application, were prepared by pyrolysis of organic precursors using thermal assisted chemical vapour deposition method. By varying the precursor concentration and preparation temperature, compositions with varying iron concentration and nanoparticle sizes were made. Powder X-ray diffraction, Transmission Electron Microscopy and MAossbauer spectroscopy studies revealed, the nanocrystalline iron carbide (Fe3C) presence in the partially-graphitized matrix. The dependence of magnetic properties on the particle size and temperature (10 K<T<300 K) were studied using Superconducting Quantum Interference Device Magnetometery. Based on the effect of surrounding carbon spins, the observed magnetic behaviour of the nanoparticle compositions, such as temperature dependence of magnetization and coercivity, can be explained.

/pdf/size-dependent-magnetic-properties-of-iron-carbide-l395f724wv.pdf

S.V. Subramanyam

Papers

Effect of sintering temperature on electrical transport properties of La0.67Ca0.33MnO3

Ferromagnetic La0.6Pb0.4MnO3 thin films with giant magnetoresistance at 300 K

Size-dependent magnetic properties of iron carbide nanoparticles embedded in a carbon matrix

Giant magnetoresistance in self-doped La1−xMnO3−δ thin films

Synthesis of multi-wall carbon nanotubes by simple pyrolysis