Experimental and theoretical assessment of Fe-doped indium-oxide-based dilute magnetic semiconductors

Specimens of iron-doped indium oxide (In_1-xFe_x)₂O₃ with x?=?0.015, 0.03, 0.045 and 0.06, amalgamated through a traditional solid-state reaction method followed by H₂/air sintering, were characterised using an X-ray diffractometer (XRD), a vibrating sample magnetometer (VSM), and a scanning electron microscope (SEM) to investigate their structural, magnetic and morphological properties respectively. According to XRD plots, all the specimens exhibit cubic bixbyite structures along with ancillary phases. Magnetic assessment showed that In₂O₃ has a negative susceptibility, exhibiting diamagnetic behaviour at room temperature. The doping of Fe ions induces ferromagnetic (FM) ordering, which is enhanced with increasing doping content. The strength of the magnetisation increases when the specimens are exposed to H₂ but is reduced on further air sintering. A bound magnetic polaron (BMP) model is successfully fitted to the observed FM data involving localised carriers and magnetic cations. A multivariate assessment viz. a hierarchical cluster analysis (HCA) was used to corroborate and strengthen the experimental determined magnetic properties. A homogeneous particle distribution was observed in all SEM micrographs and is validated through MATLAB-based simulation by applying a watershed segmentation algorithm. Surface plots also confirm the change in magnetic properties with increase in doping concentration.     

Synthesis of flower-like WS2 by chemical vapor deposition

Flower-like tungsten disulfide (WS₂) with a diameter of 5-10 μm is prepared by chemical vapor deposition (CVD). Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy are used to characterize its morphological and optical properties, and its growth mechanism is discussed. The key factors for the formation of flower-like WS₂ are determined. Firstly, the cooling process causes the generation of nucleation dislocations, and then the "leaf" growth of flower-like WS₂ is achieved by increasing the temperature.     

Investigation of mononuclear,dinuclear, and trinuclear transition metal (II) complexes derived from an asymmetric Salamo‐based ligand possessing three different coordination modes

A new asymmetric Salamo‐based ligand H₂L was synthesized using 3‐tert‐butyl‐salicylaldehyde and 6‐methoxy‐2‐[O‐(1‐ethyloxyamide)]‐oxime‐1‐phenol. By adjusting the ratio of the ligand H₂L and Cu (II), Co (II), and Ni (II) ions, mononuclear, dinuclear, and trinuclear transition metal (II) complexes, [Cu(L)], [{Co(L)}₂], and [{Ni(L)(CH₃COO)(CH₃CH₂OH)}₂Ni] with the ligand H₂L possessing completely different coordination modes were obtained, respectively. The optical spectra of ligand H₂L and its Cu (II), Co (II) and Ni (II) complexes were investigated. The Cu (II) complex is a mononuclear structure, and the Cu (II) atom is tetracoordinated to form a planar quadrilateral structure. The Co (II) complex is dinuclear, and the two Co (II) atoms are pentacoordinated and have coordination geometries of distorted triangular bipyramid. The Ni (II) complex is a trinuclear structure, and the terminal and central Ni (II) atoms are all hexacoordinated, forming distorted octahedral geometries. Furthermore, optical properties including UV–Vis, IR, and fluorescence of the Cu (II), Co (II), and Ni (II) complexes were investigated. Finally, the antibacterial activities of the Cu (II), Co (II), and Ni (II) complexes were explored. According to the experimental results, the inhibitory effect was found to be enhanced with increasing concentrations of the Cu (II), Co (II), and Ni (II) complexes.     

Air-Stable Hexagonal Bipyramidal Dysprosium(III) Single-Ion Magnets with Nearly Perfect D6h Local Symmetry

Eight-coordinated Dy^III centres with D_6h symmetry are expected to act as high-performance single-molecule magnets (SMMs) due to the simultaneous fulfilment of magnetic axiality and a high coordination number (a requisite for air stability). But the experimental realization is challenging due to the requirement of six coordinating atoms in the equatorial plane of the hexagonal bipyramid; this is usually too crowded for the central Dy^III ion. Here a hexaaza macrocyclic Schiff base ligand and finetuned axial alkoxide/phenol-type ligands are used to show that a family of hexagonal bipyramidal Dy^III complexes can be isolated. Among them, three complexes possess nearly perfect D_6h local symmetry. The highest effective magnetic reversal barrier is found at 1338(3) K and an open hysteresis temperature of 6 K at the field sweeping rate of 1.2 mT s⁻¹; this represents a new record for D_6h SMMs.     

LiB6Si: An indirect band gap semiconductor

Using first-principle calculations, mechanical properties, electronic structure, and Raman spectra of LiB₆Si structure were investigated. The band structures calculated by GGA-PBE and HSE06 methods reveal that LiB₆Si is an indirect band gap semiconductor. The band gap estimated by HSE06 method is about 2.24 eV, which is in good agreement with that of experimental value 2.27 eV. The calculated tensile stress-strain curves of LiB₆Si reveal that [010] direction is the cleavage direction under tensile strains. The calculated Raman spectra of LiB₆Si are also in good agreement with that of measured. The position of the band gap may provide a basis for further photocatalysis research on LiB₆Si.     

The effect of cationic groups on the stability of 19F MRI contrast agents in nanoparticles

Fluorine‐19 (¹⁹F)‐based contrast agents are increasingly used for magnetic resonance imaging. Conjugated to polymers, they provide an excellent quantitative imaging tool to detect the movement of the polymeric nanoparticles in vivo as there is no background signal in tissue. One of the challenges is the decline in signal intensity when the conjugated hydrophobic fluorinated functionalities aggregate. Therefore, a new fluorinated monomer was prepared from l ‐arginine that carries a 2,2,2‐trifluoroethyl functional group for imaging. The resulting monomer, 2,2,2‐trifluoroethylamide l ‐arginine methacrylamide (3FArgMA), was copolymerized with poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), [2‐(2,3,4,6‐tetra‐O‐acetyl‐α‐d ‐mannopyranosyloxy)ethyl methacrylate or 1‐O‐methacryloyl‐2,3:4,5‐di‐O‐isopropylidene‐β‐d ‐fructopyranose, respectively, using poly(methyl methacrylate) macro‐reversible addition–fragmentation chain transfer polymerization agent. The resulting block copolymers, which varied in 3FArgMA content, were self‐assembled into micelles of hydrodynamic diameters from 25 to 60 nm. The permanently positively charged arginine functionality on the 3FArgMA displayed repulsive forces against aggregation enabling high spin–spin relaxation times (T₂) in acidic as well as alkaline solutions. However, the longer poly(ethylene glycol) side functionality in PEGMEMA enabled better steric stabilization (T₂~30 ms) while the short fructose side chain was not enough to maintain high T₂ values, in particular when a higher 3FArgMA content was used. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1994–2001     

Ionic Assembly,Anion–π, Magnetic,and Electronic Attributes of Ambient Stable Naphthalenediimide Radical Ions

Organic spin-based molecular materials are considered to be attractive for the generation of functional materials with emergent optoelectronic, magnetic, or magneto-conductive properties. However, the major limitations to the utilization of organic spin-based systems are their high reactivity, instability, and propensity for dimerization. Herein, we report the synthesis, characterization, and magnetic and electronic studies of three ambient stable radical ions ( 1 a^.+ , 1 b^.+ , and 1 c^.+ ). The radical ions 1 b^.+ and 1 c^.+ with BPh₄⁻ and BF₄⁻ counter anions, respectively, were synthesized in excellent yields by means of anion metathesis of 1 a^.+ with Br⁻ as its counter anion. Notably, synthesis of 1 a^.+ was achieved in an ecofriendly, solvent-free protocol. The radical ions were characterized by means of single-crystal X-ray diffraction studies, which revealed the discrete nature of the radical ions and extensive hydrogen-bonding interactions within the radical ions and with the counter anions. Thus, radical ions can be organized to form infinite supramolecular arrays using weak noncovalent interactions. In addition, the Br⁻, BF₄⁻, and BPh₄⁻ anions formed diverse types of anion–π interactions with the naphthalene and imide rings of the radical ions. The radical ions were characterized by means of X-band electron paramagnetic resonance (EPR) spectroscopy in solution and in the solid state. Magnetic studies revealed their paramagnetic nature in the range of 10 to 300 K. The radical ions exhibited high resistivity approaching the gigaohm (GΩ) scale. In addition, the radical ions exhibited panchromism.     

Field-induced spin-polarized electronic and optical properties of armchair stanene nanoribbons

Electronic and optical properties of armchair stanene nanoribbons are studied within the $s{p}^3$ tight-binding model including spin-orbit coupling in the presence of in-plane electric field. Electric field strongly modulates energy dispersions leading to a zero-gap transition, shift in edge-states, and exhibition of spin-splitting states. Then, the complex dielectric functions in the long wavelength limit is calculated from the gradient approximation. More field-induced transition channels exhibit richer optical spectra which further reveal spin-polarized feature at low frequency. Prominent plasmons in loss spectra come from π–σ mixing orbital. The plasmon peak frequency and height are tuned by field strength. Also, the threshold plasmon frequency linearly decreases as electric field increases and it vanishes at critical field. The reflectance exhibits oscillatory behaviors and shows dip structures with sharp plasmon edge, undergoing a red-shift with increasing field. The calculated results fully show that field-modulations of electronic and optical properties strongly depend on nanoribbon's geometry.     

Ab initio and Monte Carlo studies of phase transitions and magnetic properties of YCrO3: Heisenberg model

By using the density functional theory (DFT) and Monte Carlo simulations (MCS) with the Heisenberg model, we have studied magnetic properties of the bulk perovskite YCrO₃. The exchange couplings of the Heisenberg model and the magnetic anisotropy are investigated. The 110 direction in the crystalline structure of the compound has shown the minimum energy, it is the easy magnetic direction. Using Monte Carlo simulations, the magnetizations behavior, the effects of system parameters and the critical exponents of the compound YCrO₃ are implemented. It is shown that the bulk perovskite YCrO₃ belongs to the 3D Heisenberg universality class.