Magnetic Exchange Research Articles

Mitigation of transparent exopolymer particles-induced membrane biofouling by the coupling process of magnetic ion exchange resin/ultrafiltration

The significant effects of transparent exopolymer particles (TEP) on membrane fouling have attracted the attention of several researchers. Finding an effective method for controlling membrane biofouling caused by TEP is essential for the long-term stable operation of membrane systems. The results of this experimental study show that the coupling process of magnetic ion exchange resin (MIEX)/Ultrafiltration (UF) can significantly mitigate membrane biofouling induced by TEP. Compared with the UF process, the irreversible growth rate of TEP on the membrane in the MIEX/UF process decreased by 75.9%, and the synergistic irreversible accumulation rate of TEP and bacteria decreased by 81.2%. The irreversible adhesion of bacteria to the membrane was significantly reduced, effectively inhibiting the formation of the primary level of biofilm and the development of biofouling. Further analysis showed that the MIEX inhibited the conversion of TEP precursors to TEP, and the quaternary ammonium salt functional groups on the surface of the MIEX sterilized bacteria and inhibited their proliferation in water. More importantly, because the interfacial forces between TEP/bacteria and MIEX were much higher than those between them and the UF membrane, the deposition of MIEX on the membrane surface not only prevented TEP and bacteria from reaching the membrane surface, but also removed the deposited TEP and bacteria from the membrane surface by hydraulic backwashing.

Fe30Co70/Co/CoxFe3−xO4-δ nanocomposite with multiple magnetic exchange resonance mechanisms and large magnetic loss available for microwave absorption application

Soft magnetic alloys are widely studied and reported as a type of important microwave absorption (MA) materials, while their magnetic losses are limited. In this paper, a multiphase composite strategy of the soft magnetic alloys, hard magnetic metals, and hard magnetic ferrites is adopted for increasing the magnetic loss. Then, three-phase Fe50Co50/CoxFe3−xO4-δ/γ-Fe2O3 (FC31), three-phase Fe30Co70/Co/CoxFe3−xO4-δ (FC22), and three-phase CoxFe3−xO4-δ/Co3O4/Co (FC13) nano-composites are prepared by a simple thermal decomposition process of FeC2O4 and CoC2O4 in vacuum. The crystal structure, surface composition, vibration of chemical bonds, morphology, micro-structure, and static magnetism are characterized by XRD, XPS, FTIR, Raman, SEM, TEM, and SQUID, respectively. The electromagnetic (EM) parameters are measured in 2–18 GHz by a vector network analyzer. Based on the measured EM parameters, the calculated magnetic loss tangents (tanδm) are over 0.5 in a wide frequency band of 8–18 GHz for the FC22/paraffin absorber, showing that the tanδm can be increased dramatically through the multiphase composite strategy. Benefiting from the increased tanδm, an effective absorption bandwidth of 7.0 GHz is achieved for the FC22/paraffin absorber at a thin thickness of 1.45 mm, exhibiting great application advantages in the MA field.

Low-dimensional magnetic centers in HTSC YBCO film on steel-276 induced by gamma-quanta and electron beam

Coated HTSC tapes of 2-generation based on YBa2Cu3O7-x film were irradiated with 5 MeV electron beam at 273 K to generate low-dimensional defects of atomic displacements in Cu and O sublattices for possible enhancing the magnetic flux pinning and thereby increasing the magnetic critical current. We found the optimal electron beam current and fluency, when the neighbouring linear defects are spaced so as to accommodate vortices in the undamaged superconducting area. The following 60Co gamma-irradiation at 77 K generates defect pairs and causes hole localization and increases magnetic induction. In the mixed vortex state the charge carrier pairing energy is higher than kT due to paramagnetic pinning at radiation induced defects in oxygen sublattice both in CuO chains and CuO2 planes. Such a radiation treatment of HTSC tapes is recommended for the electron beam focusing coils.

Magnetic coupling mechanism of the interface in Bi2Se3/La0.7Sr0.3MnO3

The magnetic proximity effect in Bi2Se3 (BS)/La0.7Sr0.3MnO3 (LSMO) heterostructures is studied by first-principles calculations based on the density functional theory (DFT). Two heterogeneous structures LSMO (La, Sr, O termination layer, labeled as LaSrO)/BS and LSMO (Mn, O termination layer, labeled as MnO2)/BS are configured. In the LaSrO/BS system, the larger interfacial distance (2.88 Å) and higher interfacial binding energy (−6.36 eV) indicate a greater degree of stability for this structure. The spin polarization density distribution and spin magnetic moment results show BS can be effectively magnetized in both heterostructures. The magnetic coupling effect and observed charge transfer in MnO2/BS are more pronounced, suggesting potential differences in the magnetic exchange mechanisms between LaSrO/BS and MnO2/BS. The projected density of states (PDOS) and spin polarizability suggest that electron exchange and orbital hybridization between Mn-3d orbitals and BS play a crucial role in inducing magnetic order in BS. In MnO2/BS, the magnetic proximity effect is stronger, and more spin electron transfer between Mn-d and Se-p orbital of BS. These results may promote the application of TIs in the spintronic devices field.

A DFT study on half-metallicity of Ruddlesden–Popper layered perovskite Bi8Ba4Mn8O28

Half-metallic ferromagnet has attracted intense interest due to its unique electronic structure and potential applications in spintronic devices. The structural properties, electronic structure, and magnetism are systematically investigated for Ruddlesden-Popper layered Perovskite Bi8Ba4Mn8O28 by using the first-principles calculations. It is found that Bi8Ba4Mn8O28 is a half-metallic ferromagnet with a saturated magnetic moment of 31 μB f.u.−1 at its ground state with the orthorhombic Pbnm symmetry, which ground state is determined by the symmetry analysis, and the calculations of the total energy, the formation energy, and the magnetic exchange interaction. We demonstrate that the half-metallicity of Bi8Ba4Mn8O28 is fairly robust against large uniform and tetragonal distortions. Furthermore, the surface effect on half-metallic properties is also discussed. It is shown that all terminations but Mn1O can maintain their half-metallic properties and present good robustness of half-metallicity with rather wide half-metallic gap.

Geometric factor for magnetic dipole interaction between strips

The performance of magnetic sensors is typically affected by the magnetic interaction between the surrounding components, including the magnetic dipole effect and exchange coupling. Recently, extensive studies have been carried out on the dipole interaction of filamentary samples, and the theoretical results showed good consistence with the experimental observations. However, no precise expression for the geometric factor of the magnetic dipole interaction for strip samples has been revealed. In this paper we have provided an expression for the geometric factor of the magnetic dipole interaction. The expressions of the geometric factor for strip samples are derived by means of the integration method, following the previous studies for microwires. The geometric factor of FINEMET samples was experimentally determined by calculating the magnetic field intensity and the magnetic moment at the saturation point of the hysteresis loops, which agrees well with the theoretical results. The results will provide valuable insights into the design process of magnetic sensor materials.

Tunable Spin-Polarized States in Graphene on a Ferrimagnetic Oxide Insulator.

Spin-polarized two-dimensional (2D) materials with large and tunable spin-splitting energy promise the field of 2D spintronics. While graphene has been a canonical 2D material, its spin properties and tunability are limited. Here, this work demonstrates the emergence of robust spin-polarization in graphene with large and tunable spin-splitting energy of up to 132 meV at zero applied magnetic fields. The spin polarization is induced through a magnetic exchange interaction between graphene and the underlying ferrimagnetic oxide insulating layer, Tm3 Fe5 O12 , as confirmed by its X-ray magnetic circular dichroism (XMCD). The spin-splitting energies are directly measured and visualized by the shift in their Landau-fan diagram mapped by analyzing the measured Shubnikov-de-Haas (SdH) oscillations as a function of applied electric fields, showing consistent fit with the first-principles and machine learning calculations. Further, the observed spin-splitting energies can be tuned over a broad range between 98 and 166 meV by field cooling. The methods and results are applicable to other 2D (magnetic) materials and heterostructures, and offer great potential for developing next-generation spin logic and memory devices.

Synthesis of a Novel Porous Self‐Settling Magnetic Anion Exchange Resin and its Removal Mechanism for Tannic Acid

AbstractA new porous self‐precipitating magnetic anion exchange resin (CMIET) doped with γ‐Fe2O3 was prepared by suspension polymerisation and characterized by FT‐IR, TGA, SEM, BET, and VSM. An adsorbent with a rough surface porous structure, enriched with a mesoporous strong magnetic self‐absorbent was obtained. A specific surface area of 19.10 m2/g, a pore volume of 0.2045 cm3/g, a pore size of 36.71 nm exchange capacity of 7.81 mmol/g, and an equilibrium adsorption capacity of up to 46.28 mg/g were measured. The effects of contact time, initial concentration, and solution pH were investigated by batch adsorption experiments. In the removal process, the removal rate of TA was up to 95 % at pH=4–7, saturation adsorption was achieved in 30 min, and regeneration time of 120 min could restore the resin activity. The adsorption isotherm of TA on the resin was by the Langmuir model, the adsorption kinetics was by the Pseudo Secondary Kinetic model, and the adsorption process was spontaneous heat absorption. The regeneration experiments showed good reusability of CMIET, a highly efficient and fast magnetic ion exchange resin with a wide range of applications in the aqueous environment.

Magnetic properties and entanglement of the octanuclear nickel phosphonate-based cage

The main subject considered in this paper is the quantum magnetic properties and entanglement of an octanuclear nickel phosphonate-based cage. We measured the temperature-dependent magnetic susceptibility of this cage, which indicates the coexistence of both antiferromagnetic and ferromagnetic interactions between the magnetic centers, Ni ions with spin 1. This observation prompted us to theoretically investigate the magnetic properties of such compounds. Our theoretical calculations were compared with the experimental results for magnetic susceptibility. Additionally, we explored the magnetization plateaus and magnetic susceptibility from an external magnetic field at low temperatures. We determined the thermal entanglement (negativity) and the logarithmic negativity for the octanuclear nickel phosphonate-based cage. The observed correlation between magnetization plateau jumps and magnetic susceptibility peaks in relation to the external magnetic field suggests the need for further experimental measurements.

5-Fluoro-1-Methyl-Pyrazol-4-yl-Substituted Nitronyl Nitroxide Radical and Its 3d Metal Complexes: Synthesis, Structure, and Magnetic Properties

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)2LF]2 {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)2LF]n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)2LF]2 have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)2LF]2, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)2LF]2 and [Ni(hfac)2LF]2, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)2LF]2 showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (JMn-ON = −84.1 ± 1.5 cm−1, JCo-ON = −134.3 ± 2.6 cm−1, and JNi-ON = −276.2 ± 2.1 cm−1; H^=−2JS⃑^MS⃑^NO). Notably, the magnetization of [Mn(hfac)2LF]2 having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)2LF]n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {ONO–Cu(II)–ONO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (JCu-ON = 14.8 ± 0.3 cm−1).

Selective adsorption performance and mechanism of magnetic cationic resin for emerging contaminants

The presence of emerging contaminants in the source water has become a critical issue to ensure the security of drinking water. In our study, a comprehensive investigation was carried out on the levels of three emerging contaminants (pesticides, antibiotics, and perfluorinated compounds) present in the source water from four water plants. Zero-valent iron modified cation exchange resin (ZVI-CER) and micron-sized magnetic cation exchange resin (m-MCER) were fabricated by in-situ and copolymerization methods and their removal performances for atrazine (ATZ), tetracycline (TC) and erythromycin (ETM) in water were also evaluated. The influencing parameters (pH, co-existing cations, and humic acid) of m-MCER resin were investigated in batch experiments. The removal rates of ATZ, TC, and ETM could be controlled within the ranges of 84.1–91.6 %, 65.4–91.1 %, and 82.2–99.5 % at different pH levels. Both ATZ and ETM exhibited higher resistance to different pH levels, coexisting ions (Na+, Ca2+) and humic acid during the removal process, suggesting prospective application potential for hardness removal. Whereas, TC was notably affected by the presence of NaCl, resulting in a decrease in the removal rate from 88.9 % to 61.1 %. Furthermore, the selectivity of the resin towards both emerging contaminants and coexisting cations was also examined and the sequence of selective exchange of ions in simulated water was Ca2+>Mg2+>ATZ/TC/ETM>K+>Na+. Finally, the selective adsorption mechanism of m-MCER resin for ATZ, TC, and ETM was established by analyzing various pathways, including ion exchange, hydrogen bonding and π-π stacking interactions.

Controlling electromagnetic and mechanical behaviors of geopolymer matrix with nano-SiO2@Fe3O4 magnetofluid for soft magnetic applications

Nano-SiO2@Fe3O4 magnetofluid modified geopolymer (NMMG) is presenting promising application potential in the field of magnetic building materials by virtue of its high magnetic permeability. This work aims to reveal the modification mechanisms of nano-SiO2@Fe3O4 magnetofluid on the electromagnetic and mechanical behaviors of geopolymer matrix, thus providing theoretical guidance for the engineering applications of NMMG. The results show that the introduction of nano-SiO2@Fe3O4 magnetofluid enhances the magnetic exchange energy between adjacent magnetic moments inside the geopolymer, thus weakening the coercivity by intensifying the rotation of magnetic domains inside the geopolymer, which provides a new idea for the application of NMMG in the field of soft magnetic construction materials. In addition, when the concentration of nano-SiO2@Fe3O4 magnetofluid reaches 9.4 vol%, good balance is found in the electromagnetic and mechanical behaviors of NMMG material. In that regard, NMMG can achieve satisfactory mechanical performance, ensuring as well low eddy current and hysteresis losses under alternating magnetic field, which reflects its great potential in soft magnetic applications.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

Intrinsic magnetic topological insulators (MTIs) host exotic topological phases such as quantized anomalous Hall insulating phase, arising due to the large magnetic exchange gap. However, the interplay of magnetism and topology in these systems in different temperature regimes remains elusive. In this work, we present the logarithmic temperature-dependence of conductivity for sub-100 nm thick exfoliated flakes of MTI MnBi2Te4 in the presence of out-of-plane magnetic fields and extracted the linear slope, κ. We observed a characteristic change, in the low-temperature regime, indicating the gapped Dirac surface state according to Lu–Shen theory. We also report the recovery of topological properties in the system via the weak-antilocalization effect in the vicinity of antiferromagnetic to paramagnetic transition and in the paramagnetic regime. Hikami–Larkin–Nagaoka analysis suggested the presence of topological surface states. Therefore, our study helps in understanding how intrinsic magnetism masks topological properties in an MTI as long as magnetic ordering persists.

Ab-initio and Monte Carlo studies of magnetic and magnetocaloric properties of antiperovskite Mn[formula omitted]AlN

In this study, we systematically investigate the electronic, magnetic, and magnetocaloric properties of Mn3AlN antiperovskite. This system is examined through first-principles computations using density functional theory (DFT) and Monte Carlo (MC) simulations. Based on the density of state and band structure, it is found that Mn3AlN behaves as a ferromagnetic metallic material. Additionally, we calculate the magnetic anisotropy and exchange interactions, which are parameters of the Hamiltonian, and incorporate them into the MC simulation. Concerning the magnetic properties, the critical temperature of the antiperovskite (Tc= 811 K) is almost similar to the experimental value (Tc= 818 K). Furthermore, we also investigate the magnetocaloric properties and find that the relative cooling power (RCP) values and maximum entropy change for a magnetic field strength of 5 T are 93.96 J/kg and 12.55 J/kg K, respectively. These results suggest that Mn3AlN is a promising candidate for magnetic refrigeration applications.

A Computational Exploration of Exohedrally Transition Metal Doped Si94- Superatom Based Magnetic MSi9M' Clusters (M, M' = Sc(II) to Cu(II)).

Nanosized clusters are drawing immense attention of the scientific community due to their size and composition dependent tunability of physical and chemical properties. Silicon nanoclusters are especially important because of their abundance and ample utility in the domains of electronics and semiconductor industry. Zintl phases of Si offer an excellent opportunity in the domain of nanocluster research owing to their superior stability and multifarious possibilities of tunability of electronic properties through doping with other elements. Doping silicon clusters with transition elements is a prevalent strategy to induce magnetic properties in such clusters. Although doping silicon clusters with single transition metal atoms can induce significant magnetism in nanoclusters, the dominant covalent interaction between silicon and the transition metal causes the magnetic moment to quench. The rational strategy of inducing a sustainable magnetic moment can be to introduce ferromagnetic interaction between two sites carrying nonvanishing magnetic moments. In the present work, such a possibility is explored in terms of the stability of the clusters and corresponding magnetic exchange coupling in them. The Si94-superatomic cluster is doped with two transition metal atoms exohedrally and the neutral clusters designed thereby are investigated computationally if they reduce or reinforce the high stability of the superatom and substantiate the possibility of obtaining nanosized magnetic units as building blocks of tunable materials for various applications.

MIEX resin and enhanced coagulation treatment of high-bromide natural water: Chlorine reactivity and DBP precursors removal

Both organic and inorganic constituents play a major role in the formation and speciation of disinfection by-products (DBPs) under chlorination. In this study, the removal of organic and inorganic precursors to DBPs by ion exchange and coagulation was examined, and the relationships between characteristics of dissolved organic matter (DOM), chlorine reactivity, and the formation of DBPs in high-bromide natural water were investigated. Formation potential tests were conducted for trihalomethanes (THMs) and haloacetronitriles (HANs) before and after the different treatments (coagulation, magnetic ion exchange (MIEX) resin, and combined MIEX/coagulation). At a low resin dose, MIEX was more effective than coagulation for DOM removal. The advantages of the MIEX resin were more prominent at a high resin dose because substantial amounts of DOM and bromide were simultaneously removed. The maximum bromide uptake on the MIEX resin was 0.02 mg-Br/mL. A 4-component PARAFAC model was developed using a dataset of 148 fluorescence excitation-emission matrices (EEMs) generated from pre-chlorinated and post-chlorinated samples. The maximum fluorescence intensities of humic-like components were found to be strongly correlated to THMs formation (R2 = 0.79–0.89). The MIEX treatment substantially lowered the formation of THMs (19–51%) and HANs (70–95%) due to its ability to remove humic-like DOM and bromide. The fluorescence loss for humic-like DOM was found to increase over a chlorination time of 3 days, suggesting that these compounds had stronger reactivity to chlorine compared to protein-like DOM. The chlorine reactivity of protein-like DOM increased after treatments as the residual chlorine was able to react with the less reactive fractions of DOM after chlorine-reactive compounds were removed.

Origin of Weak Magnetic Coupling in a Dimanganese(II) Complex Bridged by the Tetrathiafulvalene-Tetrathiolate Radical.

Magnetic exchange coupling (J) between different spin centers plays a crucial role in molecule-based magnetic materials. Direct exchange coupling between an organic radical and a metal is frequently stronger than superexchange through diamagnetic ligands, and the strategy of using organic radicals to engender desirable magnetic properties has been an area of active investigation. Despite significant advances and exciting bulk properties, the magnitude of J for radical linkers bridging paramagnetic centers is still difficult to rationally predict. It is thus important to elucidate the features of organic radicals that govern this parameter. Here, we measure J for the tetrathiafulvalene-tetrathiolate radical (TTFtt3-•) in a dinuclear Mn(II) complex. Magnetometry studies show that the antiferromagnetic coupling in this complex is much weaker than that in related Mn(II)-radical compounds, in contrast to what might be expected for the S-based chelating donor atoms of TTFtt. Experimental and computational analyses suggest that this small J coupling may be attributed to poor overlap between Mn- and TTFtt-based magnetic orbitals coupled with insignificant spin density on the coordinating S-atoms. These factors override any expected increase in J from the comparatively strong S-donors. This work elucidates the magnetic coupling properties of the TTFtt3-• radical for the first time and also demonstrates how multiple competing factors must be considered in rationally designing organic radical ligands for molecular-based magnetic compounds.

Realization of Robust and Ambient-Stable Room-Temperature Ferromagnetism in Wide Bandgap Semiconductor 2D Carbon Nitride Sheets.

Due to their weak intrinsic spin-orbit coupling and a distinct bandgap of 3.06 eV, 2D carbon nitride (CN) flakes are promising materials for next-generation spintronic devices. However, achieving strong room-temperature (RT) and ambient-stable ferromagnetism (FM) remains a huge challenge. Here, we demonstrate that the strong RT FM with a high Curie temperature (TC) up to ∼400 K and saturation magnetization (Ms) of 2.91 emu/g can be achieved. Besides, the RT FM exhibits excellent air stability, with Ms remaining stable for over 6 months. Through the magneto-optic Kerr effect, Hall device, X-ray magnetic circular dichroism, and magnetic force microscopy measurements, we acquired clear evidence of magnetic behavior and magnetic domain evolutions at room temperature. Electrical and optical measurements confirm that the Co-doped CN retains its semiconductor properties. Detailed structural characterizations confirm that the single-atom Co coordination and nitrogen defects as well as C-C covalent bonds are simultaneously introduced into CN. Density functional theory calculations reveal that introducing C-C bonds causes carrier spin polarization, and spin-polarized carrier-mediated magnetic exchange between adjacent Co atoms leads to long-range magnetic ordering in CN. We believe that our findings provide a strong experimental foundation for the enormous potential of 2D wide bandgap semiconductor spintronic devices.

Microstructural and magnetic properties of BiFeO3/Bi2Fe4O9 binary nanoparticles with a bimodal size distribution

Binary nanoparticles composed of BiFeO3 and Bi2Fe4O9 have attracted considerable interest due to their magnetic properties and exchange bias effect. In this paper, two samples of well-crystallized BiFeO3/Bi2Fe4O9 binary nanoparticles with varying compositions, containing approximately 3 % and 32 % of the Bi2Fe4O9 crystalline phase, were investigated to understand the impact of microstructural variations on the magnetic behavior of the samples. Both BiFeO3 and Bi2Fe4O9 phases of binary nanoparticles were synthesized in the same synthesis process by calcining amorphous precursors obtained after solvent evaporation from aqueous solutions containing iron and bismuth nitrates and tartaric acid. The identification and quantification of crystalline phases of the produced samples were performed using the X-ray diffraction technique and multiphase Rietveld refinement, respectively. The structure and microstructures of the synthesized BiFeO3/Bi2Fe4O9 nanoparticles were carried out using transmission electron microscopy techniques. The atomic composition of the samples was investigated by energy-dispersive X-ray. The magnetic properties were studied by the DC magnetization technique. Transmission electron microscopy analyses showed that both samples exhibit a bimodal particle size distribution, with average particle sizes of ∼ 116 nm and ∼ 6.5 nm for the ∼ 3 % Bi2Fe4O9 sample. In contrast, for the ∼ 32 % Bi2Fe4O9 sample the average particle sizes were ∼ 108 nm and ∼ 7 nm, respectively. Energy-dispersive X-ray analyses revealed a Fe-rich impurity phase in both samples. Temperature-dependent zero-field-cooled and field-cooled magnetization curves present a large separation between them below 300 K and zero-field-cooled curves are consistent with a broad (bimodal) size distribution of the nanoparticles for both samples. Magnetic hysteresis loops measured at 5 K after the samples are cooled from 400 K in a zero magnetic field show weak ferromagnetism for the ∼ 3 % Bi2Fe4O9 sample, whereas the ∼ 32 % Bi2Fe4O9 sample presents an improved ferromagnetism. An exchange bias-type effect was observed in both samples. The results suggest that the increase of ultrasmall Bi2Fe4O9 nanoparticles leads to an improvement in the coercivity and remanence of BiFeO3/Bi2Fe4O9 binary nanoparticles.

Novel investigation by TB-mBJ potential of magneto-electronic properties and magnetic exchange coupling in vanadium (V)-doped PbTiO3 perovskite oxide

ABSTRACT In this paper, we investigated the structural and magneto-electronic properties, and exchange coupling in new vanadium (V)-doped PbTiO3 perovskite oxide such as PbTi1−xVxO3 compounds with compositions of x = 0, 0.25, 0.5, 0.75, and 1. The calculations of these properties are based on density functional theory using the generalized gradient approximation of Wu-Cohen (GGA-WC) and the Tran-Blaha-modified Becke–Johnson potential (TB-mBJ). Our calculations with GGA-WC revealed that the lattice constant for PbTiO3 is in good concordance with other theoretical and experimental results, while for PbTi1−xVxO3 at x = 0.25, 0.5, 0.75, and 1, the lattice constant decreases with increasing vanadium concentration owing to the difference in sizes of Ti and V ionic radii. The improved electronic structures obtained by employing the TB-mBJ potential, demonstrated that the half-metallic ferromagnetic and half-metallic gaps are present in PbTi1−xVxO3 materials at x = 0.25, 0.5, 0.75, and 1, which makes them promising candidate materials for spintronics applications.