Unraveling the magnetic softness in Fe–Ni–B-based nanocrystalline material by magnetic small-angle neutron scattering

Magnetic small-angle neutron scattering is employed to investigate the magnetic interactions in (Fe0.7Ni0.3)86B14 alloy, a HiB-NANOPERM-type soft magnetic nanocrystalline material, which exhibits an ultrafine microstructure with an average grain size below 10 nm. The neutron data reveal a significant spin-misalignment scattering which is mainly related to the jump of the longitudinal magnetization at internal particle–matrix interfaces. The field dependence of the neutron data can be well described by micromagnetic small-angle neutron scattering theory. In particular, the theory explains the `clover-leaf-type' angular anisotropy observed in the purely magnetic neutron scattering cross section. The presented neutron data analysis also provides access to the magnetic interaction parameters, such as the exchange-stiffness constant, which plays a crucial role towards the optimization of the magnetic softness of Fe-based nanocrystalline materials.

Structural, Electronic, Magnetic and Mechanical Properties and Magnetocaloric Effect of the Full-Heusler Co2MnGa

Structural, electronic, magnetic and mechanical properties of the Co2MnGa have been calculated with functional density theory using full potential linear augmented plane wave method as implemented in the Wien2k code. Exchange correlation effects for these properties are treated by generalized gradient approximation while for electronic and magnetic properties, in addition to (WC-GGA) correction, mBJ-GGA scheme was also applied. The stiffness constant of the spin wave and the Curie temperature are calculated. Moreover, mechanical parameters included three elastic constants, compression modulus, Young’s modulus and shear modulus are also investigated. This theoretical study provides detailed information on the compound Co2MnGa, in different aspects and can also provide information on the application of this material. Obtained data from ab initio calculations are used as input for Monte Carlo simulations to study the magnetic properties and magnetocaloric effect. Transition temperature, magnetic entropy change, adiabatic temperature change and relative cooling power were found.

A Theory of Skyrmion Size in Skyrmion Crystals

A magnetic skyrmion is a topological object that can exist as a solitary embedded in the vast ferromagnetic phase, or coexists with a group of its "siblings" in various stripy phases as well as skyrmion crystals (SkXs). Isolated skyrmions and skyrmions in an SkX are circular while a skyrmion in other phases is a stripe of various forms. Unexpectedly, the sizes of the three different class of skyrmions depend on material parameters differently. For chiral magnetic films with exchange stiffness constant A, the Dzyaloshinskii-Moriya interaction (DMI) strength D, and perpendicular magnetic anisotropy K, κ=π2D2⁄(16AK)=1 separates isolated skyrmions from condensed skyrmion states. In contrast to isolated skyrmions whose size increases with D⁄K and is insensitive to κ<<1 and stripe skyrmions whose width increases with A⁄D and is insensitive to κ>>1, the size of skyrmions in SkXs is inversely proportional to the square root of skyrmion number density and decreases with A⁄D. This finding has important implications in searching for stable smaller skyrmions at the room temperature.

Growth and study of 4-sulfobenzenaminium potassium dihydrogenphosphate for mechanical, dielectric and photonics applications

This article describes the growth and characterization of 4-sulfobenzenaminium potassium hydrogen phosphate (SPH) sulphanilic acid with potassium dihydrogen phosphate (KDP) doped semi-organic single crystals. The crystal was grown by the slow evaporation method. Examination of the crystalline nature of the sample was carried out by single crystal X-ray diffraction and it confirmed that the sample crystallizes in orthorhombic structure in the centrosymmetric space group P212121. The optical transmittance behavior was tested by UV-Vis spectral analysis. FT-IR spectral investigations have been carried out to indicate the presence of functional groups. The chemical structure of the compound was established by 1H and 13C NMR spectra. The SHG efficiency of the powdered SPH crystal is around 1.7 times that of pure KDP. The grown crystal was stable up to 270 °C as observed from TGA and DTA curves. The microhardness test was carried out to study the load dependency of hardness. The result of this study indicates that SPH crystal is a malleable material. From the hardness values, the stiffness constant and yield strength were calculated. The dielectric response of the novel crystal was studied in the frequency range of 50 Hz to 5 MHz at various temperatures. By employing FE-SEM, the surface morphology and the particle size of the crystal were assessed.

Piperazine based Zirconium Oxy-Chloride (PzZrOCl) single crystal: A Third Order Nonlinear Optical material for Opto-electronic Device Applications

Single crystals of Piperazine Zirconium Oxy-Chloride (PzZrOCl) are grown successfully by slow evaporation technique for Opto-electronic device applications. Suitability of the material is estimated and reported as follows. Crystal habits, purity, crystallite size, microstructure and bulk crystals structures are essential parameters for device compatibility hence they were examined with basic characterization techniques and studied to estimate their effects on optoelectronic properties. The outcomes from structural aspects are reasonably good. The functional groups of a molecule, their bond vibration frequencies and mode of alignments have been examined by Fourier Transform Infrared spectroscopy (FT-IR). The transmittance (98%) in the entire visible range with lowest cut-off wavelength (215 nm) and green emission (545 nm) is another evidence of suitability. The thermal and mechanical strength via hardness, Mayer index, yield strength and elastic stiffness constant is evaluated; it is thermally stable up to 162°C, mechanically strong and belongs to soft category. Laser induced damage is estimated by using Nd:YAG laser of wavelength 1064 nm and the observed values is three times higher than KDP, 1.2 times higher than LAPP. The optical nonlinear nature and its efficiency are examined by using Z-scan technique. The analysis discussed in detailed and the results strongly recommends PzZrOCl single crystals are suitable for optical and electronic device applications.

Growth, Experimental Studies and DFT Calculations on Gallic acid 5-Nitrouracilate Single Crystals for Non-linear Optical Applications

The growth and characterization of gallic acid 5-nitrouracilate (GA5NU) single crystals were grown using slow evaporation solution growth technique at room temperature. Single crystal XRD analysis revealed that the grown crystal belongs to monoclinic crystal system. HOMO-LUMO and molecular electrostatic potential (MEP) has been visualized and analyzed. The presence of various functional groups present in the host material was examined using FTIR spectra. Mechanical stability of the grown crystal is validated using Vickers microhardness study and the grown crystal belongs to soft material category. Various hardness parameters like fracture toughness, brittleness index, elastic stiffness constant, tensile strength and other hardness parameters were also calculated. Thermal stability of the grown crystal was also determined. The second harmonic generation (SHG) efficacy of grown crystal was 2.97 times higher than potassium dihydrogen phosphate (KDP), which makes the grown crystal as suitable candidate material for non-linear optical applications.

Investigation on Chemical, Physical and Biological Assets of a Pioneering biomolecule: (2e)-3-(4-Hydroxy-3-Ethoxyphenyl)-1-(4-Hydroxyphenyl) Prop-2-En-1-One

A chalcone derivative, (2E)-3-(4-hydroxy-3-ethoxyphenyl)-1-(4-hydroxyphenyl)prop-2-en-1-one (HEHP), C17 H16 O4, has been synthesized from the mixture of 4-hydroxyacetophenone (0.05mol) and 4-hydroxy-3-ethoxybenzaldehyde (0.05mol) and by following Claisen-Schmidt reaction mechanism. Three-dimensional molecular structure, orthorhombic crystal system, and Pbca space group for the title compound were elucidated via single crystal XRD spectral study. The appearance of the vibration and absorptions for functional groups were identified using the FT-IR spectrum. 1H and 13CNMR spectra were recorded to recognize the number of unique protons and carbon environments and the best estimation of functionality based on shielding/ deshielding effects. The UV-Visible spectral study gives assistance to appreciate the absorbance and transmittance capabilities of the title molecule while Photoluminescence (PL) spectrum of the compound indicates the blue light emission in the visible region. Information regarding the endothermic and exothermic processes correlated with the sample was obtained from TG/DTA thermal analysis and the material was found to be stable up to 216°C. Mechanical properties such as the Hardness (HV), Meyer's index (n), Newtonian resistance pressure (W), load independent constant (b) and elastic stiffness constant (Cij) were calculated by performing a Vickers hardness test on the compound and they demonstrate excellent mechanical power. The as-synthesized molecule has been screened for its antibacterial, antifungal, and antioxidant activities and observed to exhibit promising activity against various microorganisms

Stripe Skyrmions and Skyrmion Crystals

Skyrmions are important in topological quantum field theory for being soliton solutions of nonlinear sigma model and magnetics for their attractive applications in information technology. Either isolated skyrmions or skyrmion crystals may exist in a given chiral magnet, but not both at the same time. When skyrmion crystals, in which skyrmions often arrange themselves into triangular lattices, can be observed in a chiral magnet, stripy spin textures in various forms appear also and even mix with skyrmion crystals. People believe that skyrmions are circular objects and stripy spin textures have zero skyrmion number. Those stripy spin textures are called anything such as spiral, helical, and cycloid spin orders, but not skyrmions. Here we present convincing evidences showing that those stripy spin textures are skyrmions, ``siblings" of circular skyrmions in skyrmion crystals and ``cousins" of isolated circular skyrmions. Specifically, isolated skyrmions are excitations of chiral magnetic films whose ground states are ferromagnetic and skyrmion formation energy is positive. When the skyrmion formation energy is negative (relative to the single domain state), condensed skyrmions are the ground states and stripe skyrmions appear spontaneously. The density of skyrmion number determines the morphology of condensed skyrmion states. At the extreme of one skyrmion in the whole sample, the skyrmion has a ramified stripe structure that maximizes the skyrmion wall length in order to lower system energy. As the skyrmion number density increases, individual skyrmion shapes gradually change from ramified stripes to rectangular stripes, and eventually to disk-like objects due to the competition between negative formation energy and stripe-stripe or skyrmion-skyrmion repulsion. At a low skyrmion number density, the natural width of stripes is proportional to the ratio between the exchange stiffness constant and Dzyaloshinskii-Moriya interaction coefficient. At a high skyrmion number density, skyrmion crystals are the preferred states. Our findings reveal the nature and properties of stripy spin texture, and open a new avenue for manipulating skyrmions, especially condensed skyrmions such as skyrmion crystals.