FRACTAL ANALYSIS OF THE MAZE-LIKE DOMAIN STRUCTURE OF FERRITE-GARNET FILMS IN THE PROCESS OF MAGNETIZATION

В данной работе с использованием комплекса экспериментальных методик и специализированного программного обеспечения исследуются магнитные висмутсодержащие феррит-гранатовые пленки, выращенные на подложках из гадолиний-галлиевого граната. Методом оптической магнитометрии получены предельные петли магнитного гистерезиса для дефектных и бездефектных участков висмутсодержащих феррит-гранатовых пленок. Установлено, что вдали от дефектов петля демонстрирует бескоэрцитивное поведение в пределах погрешности. Для случая перемагничивания вблизи дефекта появляется коэрцитивное состояние с H~1 Э. Для разных участков предельной петли магнитного гистерезиса определена фрактальная размерность. Полученные значения лежат в диапазоне D=1,35÷1,46 для произвольного участка пленки и D=1,37÷1,54 для участка с дефектами. Определены типичные морфологические характеристики поверхности висмутсодержащей ферритгранатовой пленки. Полученные результаты позволяют для эпитаксиальных висмутсодержащих магнитных пленок феррит-граната прогнозировать взаимосвязь между значением намагниченности и значением фрактальной размерности. In this work, using a set of experimental techniques and specialized software, magnetic bismuth-containing ferrite-garnet films grown on gadolinium-gallium garnet substrates are investigated. The limiting magnetic hysteresis loops are obtained by the method of optical magnetometry for defective and defect-free areas of bismuth-containing ferrite-garnet films. It was found that, far from defects, the loop exhibits a non-coercive behavior within the error limits. For the case of magnetization reversal, a coercive state with H ~1Oe appears near the defect. For different sections of the limiting magnetic hysteresis loop, the fractal dimension is determined. The obtained values are in the range of D=1,35÷1,46 for an arbitrary section of the film and D=1,37÷1,54 for a section with defects. Typical morphological characteristics of the surface of a bismuth-containing ferrite-garnet film have been determined. The results obtained make it possible to predict the relationship between the value of magnetization and the value of fractal dimension for epitaxial bismuth-containing magnetic films of iron garnet.

Asymmetric Interfacial Intermixing Associated Magnetic Coupling in LaMnO3/LaFeO3 Heterostructures

The structural and magnetic properties of LaMnO3/LaFeO3 (LMO/LFO) heterostructures are characterized using a combination of scanning transmission electron microscopy, electron energy-loss spectroscopy, bulk magnetometry, and resonant x-ray reflectivity. Unlike the relatively abrupt interface when LMO is deposited on top of LFO, the interface with reversed growth order shows significant cation intermixing of Mn3+ and Fe3+, spreading ∼8 unit cells across the interface. The asymmetric interfacial chemical profiles result in distinct magnetic properties. The bilayer with abrupt interface shows a single magnetic hysteresis loop with strongly enhanced coercivity, as compared to the LMO plain film. However, the bilayer with intermixed interface shows a step-like hysteresis loop, associated with the separate switching of the “clean” and intermixed LMO sublayers. Our study illustrates the key role of interfacial chemical profile in determining the functional properties of oxide heterostructures.

Structural and Magnetic Properties of Nano Composite (Ni1-xSrx Fe12 O19) Prepared by Sol-gel

The compound was prepared by sol-gel method for spontaneous combustion with certain weight ratios (x=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9), the samples were calcined at a temperature (900oC) for a period of two hours(2h), then studied its structural and magnetic properties.one of the most prominent results that we obtained from the X-ray diffraction technique (XRD) is that compound has several phases. Where the sample (NiFe2O4) appeared to be polycrystalline and the dominant phase in it is the cubic phase, while the other phase is (Hematite)(Fe2O3) A crystal structure rhomboid (Rhombohedral), in addition to these two phases, the phase with the existing quaternary structure appeared (Sr2Fe2O5) its called (Orthorhombic). The results of the magnetic properties that were obtained through the (VSM) device, and one of the most important of these properties is the magnetic hysteresis loop by analyzing the magnetic hysteresis loop at (x=0.3), where the least area of the hysteresis loop or the least width of the hysteresis loop One of the most important parameters of the magnetic properties is the saturation magnetism (μS) and its value ranges from (19.76-3.86) (emu/gr), the highest value was at (X=0.3) and its value is (19.76emu/gr) and in general its value decreases with increasing concentration of strontium. The residual magnetism (Mr) ranges between (7.45-1.58) (emu/gr), where it reached its highest value at (x=0.3) and its value is (7.45emu/gr), and generally its value decreases with increasing concentration of strontium. In addition to that, there is another parameter which is coercion or Magnetic coercivity (Hc) ranges in value (1751.104-209.26) (Oe), reaching its lowest value at (x=0.3), and then increases with increasing strontium concentration until it reaches its highest value at (x=0.9), where it reached its value is (1751.104Oe). The square rate represented by the symbol (μi) has high values. This means that there is a mutual coupling between the soft and hard magnetic phases, which was the highest value at (x=0.3) and its value is (4.93).

Anisotropic critical current density and flux pinning mechanism of Fe1+yTe0.6Se0.4 single crystals

Fe1+yTe0.6Se0.4 has considerable application potential due to its large critical current density (J c) and high upper critical magnetic field (H c2). However, the uncertainty of the anisotropy of J c and the unclear flux-pinning mechanism have limited the application of this material. In this study, the J c in three directions were obtained from magnetic hysteresis loop measurements. A large anisotropy of J c ab /J c c ~ 10 was observed, and the origin of the anisotropy was discussed in details. Flux pinning force densities (F p) were obtained from J c, and a non-scaling behavior was found in the normalized pinning force f p[F p/F p-max] versus the normalized field h[H/H c2]. The peaks of pinning force shift from a high h to a low h with increasing temperature. Based on the vortex dynamics analysis, the peak shift was found to originate from the magnetization relaxation. The J c and F p at critical states free from the magnetic relaxation were regained. According to the Dew-Hughes model, the dominant pinning type in Fe1+yTe0.6Se0.4 clean single crystals was confirmed to be normal point pinning.

Morphological and magnetic features of columnar nanostructures CuO

Columnar nanostructures (CNS) were grown by plasma chemical synthesis at a gas mixture pressure of 90% He + 10% O2 200 Pa and substrate temperatures of 340K (sample 1) and 370K (sample 2). The effect of substrate temperature on the morphological, crystalline, magnetic, and impedance properties of CNS was studied. Scanning microscopy (SEM) showed that the morphology of CNS varies significantly from dendritic to wire structure. Energy dispersive X-ray spectroscopy (EDS) showed a change in the stoichiometry of the deficiency samples (Cu52O48) to an excess of oxygen (Cu42O58). X-ray diffraction analysis (XRD) and Rietveld fitting showed that samples 1 and 2 have a monoclinic crystal structure with a large proportion of the amorphous phase, the size of coherent scattering regions (CSR) was 26 nm (sample 1). Magnetic measurements showed that sample 1 exhibits ferromagnetic behavior, and at 6 K a magnetic hysteresis loop appears. Sample 2 from 250 K to room temperature exhibits diamagnetic behavior. A connection was found between the appearance of diamagnetism and a jump in the dielectric constant of sample 2. An assumption was made about the electron-ionic nature of the diamagnetism of sample 2.

Magnetic Remanence of Stainless Steel and Titanium Alloy Orthopaedic Implants

Stainless steel and titanium alloys are common materials for orthopaedic implants. However there is a lack of information and studies on magnetic remanence of implants used in clinical practice. The aims of this study are to investigate the composition and the presence of magnetic remanence for these two orthopaedic implant materials. These two factors may cause implant instability and heat problems as well as degradation of the images quality if the patients undergo magnetic resonance imaging (MRI) examination. The magnetic hysteresis loop and remanence status of stainless steel and titanium alloy orthopaedic implants were investigated with a vibrating sample magnetometer (VSM). Both samples of stainless steel and titanium alloy had been exposed to external magnetic fields up to 1 T (10000 G) and 1.4 T (14000 G), respectively. The compositions of these two orthopaedic implant materials were studied using a scanning electron microscope with energy dispersive X-ray analysis (SEM-EDX). The results of the study demonstrated that ferrous and nickel compositions in stainless steel alloy orthopaedic implants contributed to the residual magnetism, as shown in the hysteresis loop. The titanium alloy orthopaedic implant sample does not contain any ferromagnetic elements. After exposure to a magnetic field, the stainless steel values of retentivity, coercivity and magnetisation are significantly higher compared to those of the titanium alloy. The stainless steel orthopaedic implant sample demonstrates a typical hysteresis loop that suggests the existence of magnetic remanence. In contrast, the titanium alloy orthopaedic implant sample showed no significant remanence phenomenon. By considering the existence of magnetic remanence in the implant is important as potential effect on the MRI image quality.

Magnetic Properties of a Ni Nanonet Grown in Superfluid Helium under Laser Irradiation

A nanonet consisting of ultrathin Ni nanowires (diameter <4 nm) and Ni nanoballs (diameter <20 nm) has been grown through laser ablation of a Ni target in superfluid helium. At a low Ni concentration, the nanonet consists mainly of nanowires and manifests a rectangular magnetic hysteresis loop, while an increase in the Ni concentration results in an increase in both the concentration and diameter of the nanoballs. A decrease in hysteresis loop rectangularity is observed as the concentration of the nanoball increases. We show that the composition of the system can be determined from the changes in the magnetic hysteresis loop and the temperature dependence of magnetization. The significance of the work consists of the observation of evolution of magnetic properties of the ferromagnetic nanonet, while its composition varies from nanowires to a combined nanowires–nanoballs system.

SOLVOTHERMAL SYNTHESIS AND CHARACTERIZATION OF POROUS Co MICROSPHERES

Porous cobalt (Co) microspheres were successfully synthesized via a facile surfactant-free solvothermal route. These microspheres have an average diameter of about 2 µm, assembled by many primary Co nanosheets. A possible formation mechanism of porous Co microspheres is discussed. The magnetic hysteresis loop shows a ferromagnetic feature of porous Co microspheres and the saturation magnetization (Ms) and coercivity (Hc) are 115.3 J/T·kg and 6.883 kA/m, respectively.

Low-Coordinate Dinuclear Dysprosium(III) Single Molecule Magnets Utilizing LiCl as Bridging Moieties and tris(amido)amine as Blocking Ligands

A low-coordinate dinuclear dysprosium complex {[Dy(N3N)(THF)][LiCl(THF)]}2 (Dy2) with a double bridging ‘LiCl’ moiety and tris(amido)amine (N3N)3- anions as a blocking ligand is synthesized and characterized structurally and magnetically. Thanks to the use of the chelating blocking ligand (N3N)3− equipped with large steric –SiMe3 groups, the coordination sphere of both DyIII ions is restricted to only six donor atoms. The three amido nitrogen atoms determine the orientation of the easy magnetization axes of both DyIII centers. Consequently, Dy2 shows slow magnetic relaxation typical for single molecule magnets (SMMs). However, the effective energy barrier for magnetization reversal determined from the AC magnetic susceptibility measurements is much lower than the separation between the ground and the first excited Kramers doublet based on the CASSCF ab initio calculations. In order to better understand the possible influence of the anticipated intramolecular magnetic interactions in this dinuclear molecule, its GdIII-analog {[Gd(N3N)(THF)][LiCl(THF)]}2 (Gd2) is also synthesized and studied magnetically. Detailed magnetic measurements reveal very weak antiferromagnetic interactions in Gd2. This in turn suggests similar antiferromagnetic interactions in Dy2, which might be responsible for its peculiar SMM behavior and the absence of the magnetic hysteresis loop.