Electronic surface states localized on the edge of a semi-infinite square lattice are studied in the tight binding approximation. We examined the existence of surface states in the presence of magnetic field applied in the surface region of a 2D lattice. The applied field is perpendicular to the lattice and confined to a stripe near the surface. We also included a surface site perturbation caused by the presence of the surface. The magnetic field is introduced into the model by the Peierls substitution.
We studied magnetic properties of perovskite-type Y_{0.33}Sr_{0.67} CoO_{2.614} and Y_{0.33}Sr_{0.67}CoO_{2.707} prepared under different sintered temperatures at 1250ºC and 1100ºC, respectively. A dc magnetization jump associated with a large thermal hysteresis around 180 K was found in Y_{0.33}Sr_{0.67}CoO_{2.614}, which indicates a kind of magnetic memory effect. On the other hand, Y_{0.33}Sr_{0.67}CoO_{2.707} shows a larger magnetization with a small magnetization jump around 200 K and lower Curie temperature than those of Y_{0.33}Sr_{0.67}CoO_{2.614}. Rich Co^{3+} ions in the low temperature sintered Y_{0.33}Sr_{0.67}CoO_{2.707} possibly introduce large magnetization and high magnetization jump temperature. This may be coming from a surface/volume effect of Co^{3+} ions appearing in the polycrystalline sample prepared at low temperature. The ferromagnetism resulted from the different surface/volume ratio contributes to a part of magnetization and may result in the change of the Curie temperature.
We study the effect of nanometric size on the crystal structure, magnetic environment of iron and magnetization in NdFeO₃ system of nanoparticles. The average particle size of NdFeO₃ nanoparticles increases with annealing at 600°C from about 15 nm to 40 nm. The smallest particles on annealed sample have size approximately 30 nm and typically have character of single crystalline samples. All samples adopt orthorhombic crystal structure, space group Pnma with lattice parameters a =5.5817 Å, b=7.7663 Å and c =5.456 Å for as prepared sample. The presence of superparamagnetic particles was indicated by the Mössbauer measurements. The reduction of dimensionality induces a decrease of T_{N1} from 691 K to 544 K. The shift of magnetic hysteresis loop in vertical and horizontal direction was observed at low temperatures after cooling in magnetic field. We attribute such behaviour to exchange bias effect and discuss in the frame of core-shell model.
The growth of nanostructured materials by means of different deposition methods employing nanoporous anodic aluminum oxide membranes as patterned templates has been widely used during last years due to the outstanding features displayed by these nanoporous templates. Here we report on the synthesis, morphology and magnetic properties exhibited by novel magnetic 1D and 2D nanostructured materials having nanowire or antidot thin films geometry, respectively, together to that of geometrically diameter modulated ferromagnetic nanowires. Their magnetic properties will be analyzed and discussed based on the different anisotropic behavior derived from their morphological and microstructural features.
This paper is devoted to studies of the structural and magnetic properties of Co_2FeSi Heusler alloy produced by arc melting resulting in samples with large grains compared to finer-grained ribbon type samples prepared by planar flow casting. The scanning electron microscopy completed by energy dispersive X-ray spectroscopy, X-ray diffraction, and magnetic methods sensitive to both bulk and surface were applied. The chemical composition inside the grains was found to be in agreement with the nominal one while at the grain boundaries enrichment on Co and Si at expense of Fe was observed. The magnetic parameters derived from the bulk hysteresis curves resulted in nearly the same values of coercivity, about 1 kA/m, for both technological procedures while magnetization was of about 15 A m²/kg higher at ribbons compared with sample prepared by arc melting, 145 A m²/kg. The surface magnetic characteristics were visibly influenced by a surface magnetic anisotropy. The smooth polished surface of the sample prepared by arc melting has allowed visualizing the magnetic domain structure inside the grains and at grain boundaries by the magneto-optical Kerr microscopy and magnetic force microscopy.
The present paper is devoted to Fe-Al alloys with aluminium content of 28, 33 and 35 at.%, prepared by standard technological procedure. The attention is focused on the comparison of the surface and bulk magnetic properties, which were obtained by magneto-optical Kerr effect (MOKE) and atomic and magnetic force microscopy (AFM/MFM) as the surface-sensitive methods combined with the vibration sample magnetometer (VSM) yielding the bulk magnetic properties. As was expected, the Fe_{72}Al_{28} sample shows an overall ferromagnetic behavior at room temperature. Nevertheless, the bulk hysteresis loop shows single-phase behavior, while the surface MOKE hysteresis loop consists of two overlapped curves characterized by different coercivity values. The other two samples are paramagnetic from the viewpoint of the bulk, but reveal ferromagnetic behavior of their surfaces, represented by hysteresis loops, corresponding to rather harder magnetic phase. These results are well supported by MFM.
Magnetic force microscopy measurements combined with computer simulations were applied to investigate the strengths of magnetic field over the [NiFe/Au/Co/Au]_N multilayers with in-plane and out-of-plane anisotropy observed for NiFe and Co layers, respectively. All measurements were performed in air atmosphere at room temperature. Dimensions and density of magnetic domains were estimated. The distribution of magnetization directions was deduced from comparison of magnetic force microscopy with the simulation results. Some sort of modulation in stray magnetic field was observed, but till now it is of unknown origin.
In this work we report results of ferromagnetic resonance studies of a 6% 15nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5 K and 120 K. We observe a temperature induced reorientation of the effective in-plane easy axis from [\overline{1}10] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H_{eff} (=4π M-H_{2⊥}), H_{2∥}, and H_{4∥}. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In "fitting" mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations.
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