Magnetotransport properties of the Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayer and the Pr0.5Ca0.5MnO3 and La0.7Sr0.3MnO3 films deposited on LaAlO3 (001) substrate by pulse laser deposition were investigated. X-ray diffraction and high-resolution electron-microscopy analysis reveal that lattice parameters for the constituent sublayers in the bilayer are very close to those for the individual films. It was found that a ferromagnetic transition in the La0.7Sr0.3MnO3 sublayer significantly modifies magnetotransport properties of the Pr0.5Ca0.5MnO3 constituent sublayer due to the magnetic proximity effect. Evidence of this effect includes the appearance of exchange bias interaction between the constituent sublayers, a localized-to-itinerant crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferromagnetic state, and an unusual polar transport of carriers. Experimental results were analyzed within the framework of the modern theoretical approach. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677235]

Magnetotransport properties of the Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayer and the Pr0.5Ca0.5MnO3and La0.7Sr0.3MnO3 films deposited on LaAlO3 (001) substrate by pulse laser deposition were investigated. X-ray diffraction and high-resolution electron-microscopy analysis reveal that lattice parameters for the constituent sublayers in the bilayer are very close to those for the individual films. It was found that a ferromagnetic transition in the La0.7Sr0.3MnO3 sublayer significantly modifies magnetotransport properties of the Pr0.5Ca0.5MnO3 constituent sublayer due to the magnetic proximity effect. Evidence of this effect includes the appearance of exchange bias interaction between the constituent sublayers, a localized-to-itinerant crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferromagnetic state, and an unusual polar transport of carriers. Experimental results were analyzed within the framework of the modern theoretical approach.

The increasing interests in magnetic nanoparticles has prompted research on ferritin, which is naturally a well-defined iron-storage protein in most living organisms. However, the exact magnetic behavior of ferritin is not well understood, because the crystal structures of ferritin and ferrihydrite, its major component, are not fully understood. Briefly, we discuss the previous magnetization models of ferritin and ferrihydrite and we present a new model (Σ3L) of the initial magnetization of ferritin, considering its different phases. The new model includes three Langevin-function terms, which represent three different magnetic moments provided by the likely hydroxide and oxide mineral phases in ferritin. Compared to previous models, our simple model fits the experimental data 12 times better in terms of the sum of least squares. The magnetic independence of each component supports the multi-phase compositional model of the mineral core of horse-spleen ferritin. This Σ3L model gives a quantization of the amounts of the different phases within horse-spleen ferritins that matches other published experimental data: 60–80% ferrihydrite, 15–25% maghemite/magnetite, and 1–10% hematite.

Nd0.52Sr0.48MnO3 films of various thicknesses have been prepared by dc magnetron sputtering on single crystal LaAlO3 (001) substrates. Reducing the film thickness leads to a significant suppression of ferromagnetic (FM) ordering and the Curie point falls below the antiferromagnetic (AFM) transition temperature. When this occurs, a huge rise of the magnetoresistance ratio from 400 to 60 000% is observed in an applied magnetic field of 5 T. We surmise that this new kind of the enhanced colossal magnetoresistance effect originates in the FM/AFM competition and the collapse of the charge-ordered state at high magnetic fields, rather than in the regular double-exchange mechanism.

X-ray diffraction analysis and high-resolution electron microscopy of BiFeO3 films prepared by dc magnetron sputtering on single-crystal LaAlO3 (001) substrates reveal that the films have a highly c-oriented orthorhombic crystalline structure. The magnetic properties of the BiFeO3 films are typical of ensembles of interacting superparamagnetic clusters, rather than Dzyaloshinskii-Moriya weak ferromagnets. The appearance of extrinsic nanoscale superparamagnetic clusters is explained by an oxygen deficiency in certain regions of the film, where ferromagnetic ordering can be realized through a double-exchange Zener mechanism.

Nd 0.52 Sr 0.48 Mn O 3 films have been fabricated by dc magnetron sputtering on single-crystal LaAlO3 (001) and SrTiO3 (011) substrates with additional annealing to relax the lattice strain. Although the Nd0.52Sr0.48MnO3 films were deposited simultaneously on different substrates at the same deposition rate, they differ in thickness by a factor of ≃2. The observed difference in thickness is explained by the two-dimensional (layer-by-layer) film growth, rather than by a difference in growth rate controlled by the crystalline orientation of the substrate. An analysis of optical and transport properties reveals that the observed anisotropy in the polaron motion is governed by a strong anisotropy in the trapping energy, rather than in polaron formation. It is shown that the deposited Nd0.52Sr0.48MnO3 films exhibit magnetic behavior typical of two-phase magnetic systems and should be regarded as an assembly of interacting magnetic clusters.

The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La0.45Sr0.55Mn1−xCoxO3 (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La0.45Sr0.55MnO3 undergoes a paramagnetic–ferromagnetic transition at TC=290K and a ferromagnetic–antiferromagnetic transition at TN=191K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn3+–Mn4+ double-exchange interaction and induces the Co2+–Mn4+ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above TC exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity.

The structural and the magnetic properties of Zn1−xNixFe2O4 (x=0, 0.20, 0.40, 0.60, 0.80, and 1.00) nanoparticles were investigated. The structure and the particle size were measured by x-ray diffraction and scanning electron microscopy. For ZnFe2O4 nanoparticle, particle-size reduction induces the ionic exchange between Zn and Fe ions and promotes the formation of ferrimagnetic (FI) clusters. For NiFe2O4, particle-size reduction causes surface spin disorder in nanoparticles, suppressing the ferrimagnetism. For the Zn-rich Zn1−xNixFe2O4 (x=0.20 and 0.40) nanoparticles, the Ni doping in ZnFe2O4 promotes the ionic redistribution, resulting in the enhancement of FI clusters and a strong ferrimagnetism. For the Ni-rich Zn1−xNixFe2O4 (x=0.60 and 0.80), the Zn doping in NiFe2O4 also induces strong ferrimagnetism since it decreases the magnetic moment of A sublattices and weakens the surface spin disorder in nanoparticles. Spin-glasslike behavior in the series of samples is reported. Especially for NiFe2O4, through measuring the ac susceptibility and employing the critical power and the Vogel–Fulcher models, the dynamics of spin-glasslike state is discussed.

The mixed-state superconducting properties of bulk MgB2+2at.%TiO2 and +8at.%SiC, prepared by in situ solid state reaction, are investigated. Analysis of the mixed-state parameters, such as the upper critical field, the coherence length, and the Ginzburg-Landau parameter, proves that MgB2+2at.%TiO2 is a high-κ type-II superconductor in the dirty limit, while MgB2+8at.%SiC corresponds to that in the moderately clean limit. It is shown that the grain-boundary pinning realized in fine-grained doped MgB2 polycrystals is of the anisotropic rather than the electron-scattering type. The field-cooled temperature dependences of the magnetic moment reveal a transition of the samples to the paramagnetic state at certain applied magnetic fields, which is treated as manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the base of modern theoretical approaches.

A giant diamagnetism in the Co$_{2}$CrAl compounds, in both bulk and thin film, below a certain temperature ($T_z$) was observed. Above $T_z$, the compound behaves as an ordinary ferromagnet. The diamagnetic alignment might be initiated by the Landau diamagnetism because of the half-metallic properties and the pinning of the diamagnetism is preserved by the peculiar electronic structures.

Microstructural, magnetic, and transport properties of as-deposited La0.9Ce0.1MnO3 films prepared by pulse laser deposition have been investigated. The high-resolution electron-microscopy study reveals that films have a high c-oriented texture with a negligible quantity of CeO2 inclusions. The observed Griffiths-type magnetic behavior above the Curie point and the partial transition of the film into the antiferromagnetic state with decreasing temperature are attributed to the microstructural peculiarities.

We fabricated two-dimensional (2-D) Co magnetic arrays starting from a 40-nm-thick Co layer on a 6-in. Si wafer by photolithography with a KrF laser source and the wet-etching process. Various patterns, including square and triangular lattices, were achieved, with their smallest feature size ranging from 300 to 800nm. In this paper, we present the key processes to prepare nano-scaled 2-D magnetic arrays and the fabricated structures, along with their magnetic properties.