Fabrication of exchange coupled hard/soft magnetic nanocomposites: Correlation between composition, magnetic, optical and microwave properties

First principles calculation to investigate the effect of Mn substitution on Cu site in CeCu3-x Mn x V4O12 (x = 0, 1, 2 and 3) system

Structural, electronic, elastic and magnetic properties of CeCu3-x Mn x V4O12 (x = 0, 1, 2 and 3) system have been carried out through DFT using GGA, GGA+U and HF potential. The investigation of structural optimization reveals that lattice parameters of the understudy system is reliable with the reported results and are increasing with the Mn substitution due to their greater atomic radii as compare to Cu atom. Both the cohesive energy and the enthalpy show that CeCu3V4O12 is the most thermodynamically stable among these compounds. When Mn is replaced by Cu in these compounds, not only it become semi-metals, but the host compound also changes from non-magnetic to anti-ferromagnetic and their electrical resistance provides further credence to their electronic behavior. Mechanical stability, anisotropy, and ductility are all demonstrated through the elastic characteristics of these compounds. Due to anti-ferromagnetic ductile nature of the Mn base compounds, it is expected that the compounds in the system may use for spintronic application and in magnetic cloaking devices.

Microstructure and high frequency electromagnetic parameters of the soft/soft (CoFe2O4) x : (Ni0.4Cu0.2Zn0.4Fe2O4) y nanocomposites

The soft/soft (CoFe₂O₄) _x  : (Ni_0.4Cu_0.2Zn_0.4Fe₂O₄) _y (CFO _x /NCZO _y ) nanocomposites (NCs) based on spinel ferrites were produced by the sol-gel method with varying phase's ratio (x : y = 0 : 1; 1 : 1; 2 : 1; 3 : 1; 1 : 3; 1 : 2 and 1 : 0). All NCs consisted of 2 single phases (initial spinels) without any impurities and the absence of chemical interaction between phases. Structural features were investigated and analyzed. The varying of the structural parameters was non-linear and correlated well with the lattice parameter for initial components. There were two maxima observed for all NCs on particle size distribution. It was demonstrated that an increase in the CFO content leads to an increase in the most probable size of the coarse fraction and a decrease in the most probable grain size of the fine fraction. An increase in the NCZO content leads to a decrease in the average size of both fine and coarse fractions. This is obviously due to the large number of defects in the NCZO crystal lattice. The high frequency electromagnetic parameters (real and imaginary parts of the permittivity and permeability, reflection losses) were analyzed in the range of 2-10 GHz. The increase of the energy losses with frequency increase was observed. The nature of the attenuation of the reflected energy associated with the electromagnetic absorption processes due to magnetic losses. Maximal values of the electromagnetic absorption were observed for CFO₂/NCZO₁ (-18.9 dB). This correlates with the lattice parameters of the composites. The result of the electromagnetic characteristics opens broad perspectives for practical applications such kind of NCs for antenna technology (5G technology) and for electromagnetic absorbing coatings.

The Interrelation of Synthesis Conditions and Wettability Properties of the Porous Anodic Alumina Membranes

The results of studies on the wettability properties and preparation of porous anodic alumina (PAA) membranes with a 3.3 ± 0.2 μm thickness and a variety of pore sizes are presented in this article. The wettability feature results, as well as the fabrication processing characteristics and morphology, are presented. The microstructure effect of these surfaces on wettability properties is analyzed in comparison to outer PAA surfaces. The interfacial contact angle was measured for amorphous PAA membranes as-fabricated and after a modification technique (pore widening), with pore sizes ranging from 20 to 130 nm. Different surface morphologies of such alumina can be obtained by adjusting synthesis conditions, which allows the surface properties to change from hydrophilic (contact angle is approximately 13°) to hydrophobic (contact angle is 100°). This research could propose a new method for designing functional surfaces with tunable wettability. The potential applications of ordinary alumina as multifunctional films are demonstrated.

A Study of Ta2O5 Nanopillars with Ni Tips Prepared by Porous Anodic Alumina Through-Mask Anodization

The paper discusses the formation of Ta₂O₅ pillars with Ni tips during thin porous anodic alumina through-mask anodization on Si/SiO₂ substrates. The tantalum nanopillars were formed through porous masks in electrolytes of phosphoric and oxalic acid. The Ni tips on the Ta₂O₅ pillars were formed via vacuum evaporation through the porous mask. The morphology, structure, and magnetic properties at 4.2 and 300 K of the Ta₂O₅ nanopillars with Ni tips have been studied using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The main mechanism of the formation of the Ta₂O₅ pillars during through-mask anodization was revealed. The superparamagnetic behavior of the magnetic hysteresis loop of the Ta₂O₅ nanopillars with Ni tips was observed. Such nanostructures can be used to develop novel functional nanomaterials for magnetic, electronic, biomedical, and optical nano-scale devices.

The Positive Temperature Coefficient of Resistivity in BiFeO3 Films

The use of lead-free ceramic film materials with positive temperature coefficient of resistivity (PTCR) is widespread in temperature heaters and sensors in micro-electromechanical systems. In this research, the out of plane transport properties of the BiFeO₃ (BFO) films have been studied. Surprisingly, PTCR was found in the BFO ceramic films due to the strongly correlated interaction between the multiferroic material BFO and the superconductor YBCO perovskite oxides. To our knowledge, this is the first report on the PTCR effect of BFO films. The BFO/YBCO interface and the bulk conductivity of BFO are important for the PTCR effect, as they make it possible to compare the transport properties of Au/BFO/YBCO- and YBCO/BFO/YBCO-type structures. PTCR was observed in Au/BFO/YBCO at a bias voltage of more than 2 V, but not in the YBCO/BFO/YBCO, even with a 40 V bias voltage. PTCR was found after BFO breakdown of a YBCO/BFO/YBCO capacitor. This indicated that the conductivity of BFO is critical for PTCR. The dependence of PTCR on the superconducting transition temperature illustrates that a cooper-pair can be injected into BFO. Our work presents a method by which to produce a lead-free ceramic film material with PTCR.