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Magnetic nanometric skyrmions are small complex vortex-like topological defects, mainly found in non-centrosymmetric crystals such as MnSi. They have potential applications for future spintronic devices. In this article, the structural, electronic, and magnetic states of the Mn atoms in a polycrystalline MnSi thin film facing a c-sapphire substrate were studied using x-ray diffraction, x-ray photo-emission spectroscopy, resonance photoemission spectroscopy (RPES), and extended x-ray absorption fine structure (EXAFS). The valence band spectra indicate the metallic nature of the film. The RPES study reveals the presence of major itinerant Mn 3d states near EF and also the mixed Mn 3d and Si 3s–3p states from 5.3 to 11.3 eV. The EXAFS spectrum does not show the existence of oxygen vacancies in the system, and the obtained magnetic moment in the non-stoichiometric MnSi thin film is a combination of the partially itinerant and partially localized Mn 3d states. [ABSTRACT FROM AUTHOR]

A comparative study has been made for the defect induced room temperature ferromagnetism of single crystal, poly-crystal, and nanorod zinc oxide (ZnO), based on the magnetic properties and electronic properties by means of X-ray absorption near edge structure spectroscopy (XANES), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), valence band photoemission spectroscopy (VB-PES), and SQUID-type magnetometry. Magnetic measurement demonstrates the defect-induced ferromagnetic nature at room temperature in different ZnO films and a strong correlation between their electronic properties and magnetic responses. The higher ferromagnetic behaviour in polycrystalline ZnO is attributed to the increasing number of surface defects and native defect sites (oxygen vacancies and zinc interstitials) present in ZnO. XANES studies reveal that the number of unoccupied p states in polycrystalline ZnO is higher than single crystal ZnO as well as nanorod ZnO. The more amount of oxygen vacancy causes the highest intensity the O 1 s peak to appear in the XANES spectra of polycrystalline ZnO. In polycrystalline ZnO, the binding energy of the Zn 2p3/2 core level peak shifted to lower energy that further confirms the increase of the valence band maximum (VBM) position. The VBM of single crystal, poly-crystal, and nanorod-ZnO is 3.64 eV, 3.99 eV, and 3.71 eV, respectively, obtained from UPS (He-I) measurements. VB-PES studies confirm that the number of electrons in the valence band of O 2p - Zn 4sp hybridized states of poly-crystal ZnO is higher than single crystal and nanorod-ZnO. [ABSTRACT FROM AUTHOR]

In this report, we present the temperature dependence of the magnetic coercivity of graphene oxide (GO) and reduced graphene oxide (RGO). We observe an anomalous decrease in coercivity of GO and RGO with decreasing temperature. The observation could be understood by invoking the inherent presence of wrinkles on graphene oxide due to presence of oxygen containing groups. Scanning electron microscopic image reveals high wrinkles in GO than RGO. We observe higher coercivity in RGO than in GO. At room temperature, we observe antiferromagnetic and ferromagnetic behaviours in GO and RGO, respectively. Whereas, at low temperatures (below T = 60-70 K), both materials show paramagnetic behaviour. [ABSTRACT FROM AUTHOR]

In this report, we have investigated the effect of antisite ordering on the magnetic behavior of NixZn1-xFe2O4 nanoparticles for x = 0, 0.25, 0.5, 0.75, and 1. Observed magnetization versus temperature data show systematic gradual changes from antiferromagnetic to ferrimagnetic phase with increasing amount of Ni concentration. Saturation magnetization of the parent Zn ferrite increases when substituted by Ni and then decreases for concentration greater than x = 0.5. Coercivity also shows a concentration dependence. Saturation magnetization has no dependence on cooling field at all concentrations. For x = 0.5 the system act as an extremely soft magnetic material with highest saturation magnetization and lowest coercivity. Site occupancy by cations plays an important role for local moment imbalance between different antiferromagnetic sublattices giving rise to ferrimagnetic interaction upon Ni substituted in Zn ferrite. [ABSTRACT FROM AUTHOR]

In this paper, we show that when nanoparticles of Fe3O4 are coated with gold there is a distinct enhancement of magnetization by a factor of six. This increase of magnetization has been attributed to large orbital magnetic moment formation at the magnetic particle/Au (core/shell) interface. Our theoretical analysis indicates that the enhanced magnetism observed in Fe3O4-Au (core-shell) nanoparticles is an interfacial effect. The origin of magnetism in Au as an interfacial phenomenon is supported by the observation of positive magnetization in citrate coated gold nanoparticles. In citrate coated gold nanoparticles, we observe a crossover from positive magnetization value to negative magnetization value upon increasing magnetic field indicating cancellation of interfacial magnetization by the diamagnetic contribution from the bulk. We propose a theoretical formalism which semi-quantitatively explains our experimental results and supports the origin of magnetization in Au as an interfacial effect. [ABSTRACT FROM AUTHOR]

Magnetic properties of mechanical alloyed α-Fe1.4Ti0.6O3 were studied at broad scale of temperatures, starting from room temperature down to 5 K. Morin transition of the base compound α-Fe2O3 was not observed after Ti doping. Enhanced ferromagnetism and exchange bias effect were exhibited in the alloyed compound α-Fe1.4Ti0.6O3. The observations were examined from different aspects of the alloying process, e.g., magnetic solution (spin ordering) at the interfaces of rhombohedral planes and core-shell structure of the nano-grains. Interfacial magnetic modifications were seen to be affected by the factors associated with grain size variation during alloy formation and thermal annealing of the alloy. Detailed analyses were made to understand the surface magnetism and exchange bias effect in the samples. Magnetic features of the present samples in many cases were found to be unconventional in comparison with the simple grain size effect of magnetic particles. [ABSTRACT FROM AUTHOR]

The effects of particle size, structure, microstrain, and cation distribution on magnetic property of nanosized Ni0.35Zn0.65Fe2O4 prepared through high-energy ball milling have been explored by a wide variety of experimental technique namely, x-ray diffraction, high-resolution transmission electron microscopy, dc magnetization measurement, and Mössbauer spectroscopy. The sample exhibits mixed magnetic behavior with a collective magnetic state between 300 and 60 K while spin glasslike freezing of magnetic moments has taken place below 60 K. The sample has displayed enhancement in magnetization, magnetic hyperfine field, coercivity, and anisotropy energy. The inherent superparamagnetic relaxation of ferrite nanoparticles has significantly reduced and it shows evidence of magnetic hysterisis at room temperature. These properties could be profitably used to overcome the inherent instability of magnetic nanoparticles. The intersublattice interaction (JAB) in the sample has strengthened due to migration of Fe3+ ions from octahedral (B) site to tetrahedral (A) site and this accounts for the genesis of counterintuitive magnetic enhancement in the sample. [ABSTRACT FROM AUTHOR]

Silver nanoparticles of diameters in the range of 4.2–46 nm have been used to grow nanoshells of lithium niobate with thicknesses in the range of 2.2–22 nm in a silicate glass matrix. The lithium niobate shells form a percolative network and show electronic conduction. This has been explained as due to Mott’s variable range hopping conduction mechanism. The hopping is interparticle because the density of localized states is found to be in reasonable agreement with the density of nanoparticles with a core-shell structure. The ac conductivity is shown to be dependent on frequency with the exponent having a value around 0.5. This arises due to the charge motion’s being operative in a two-dimensional structure with one of these dimensions involved in such motion. Optical absorption of the core-shell structured nanoparticles exhibits two peaks—one around 350 nm is ascribed to plasmon resonance of silver nanoparticles which are not covered by a niobate shell, and the other in the range of 550–650 nm is caused by light scattering from the core-shell structure. [ABSTRACT FROM AUTHOR]

Nanocomposites containing silver particles of diameter of 20 nm with silver orthosilicate crystals forming the shell with thickness around 21 nm closely packed in a silicate glass were prepared. The ac conductivity of samples subjected to different heat treatments were measured over the frequency range of 100 Hz to 6 MHz in the temperature range of 500–570 K. The data were analyzed by the Macdonald model based on Kohlrausch-related frequency response formalism designated as CK0. The reference system was taken as the glass-crystal composite containing a lithium orthosilicate crystalline phase. The shape parameter βo for the reference system was found to be 0.33, whereas that for the nanocomposites was extracted to be 0.46. The former implied a one-dimensional lithium ion motion along the grain boundaries of the orthosilicate crystals, whereas the latter indicated that there was a one-dimensional silver ion motion in an effective two-dimensional structure in the shell surface because of a high stress condition along the radial direction of the core-shell composite. [ABSTRACT FROM AUTHOR]