Tunable Magnetic Properties Research Articles

Facile Synthesis of Cobalt-Doped Porous Composites with Amorphous Carbon/Zn Shell for High-Performance Microwave Absorption.

A facile method for the preparation of microwave absorbers with low density, high microwave absorptivity, and broad band is of paramount importance to the progress in practical application. Herein, commonly-used metal organic frameworks (MOFs) prepared just by mechanical stirring in methanol at room temperature were chosen as sacrificial templates to synthesize porous carbon composites with tunable dielectric and magnetic properties. With the replacement of Co atoms on the surface of zeolitic imidazolate framework-67 (ZIF-67) by Zn atoms, a Co-doped porous carbon composite with a low-dielectric amorphous carbon/Zn shell was constructed after annealing, leading to excellent impedance matching condition. Consequently, the as-obtained composite (Co/C@C-800) shows marvelous microwave absorption properties with an absorption capacity of −43.97 dB and a corresponding effective absorption bandwidth of 4.1 GHz, far exceeding that of the traditional porous carbon and composites directly derived from ZIF-67. The results provide a convenient way to modify MOFs for enhanced microwave absorption materials from the synergy of dielectric and magnetic losses.

Click chemical assembly and validation of bio-functionalized superparamagnetic hybrid microspheres

Surface derivatized magnetic nanoparticles have been commonly used for magnetic separation. Facile mechanisms are needed to be developed for the design of bio-functionalized magnetic hybrid materials, where the surfaces can be re-generated for the re-use of the developed platforms. Superparamagnetic iron oxide nanoparticles with a diameter below 10 nm were synthesized via a novel microwave-assisted hydrothermal method in the presence of citrate ions, which allowed to obtain uniform and negatively charged nanoparticles. These were then coupled with Poly-l-lysine (PLL), forming micrometer-sized self-assembled spherical entities. Cross-linking the PLL within these microspheres with glutaraldehyde stabilized them chemically and mechanically. The active bio-functionality was introduced by a protein grafting methodology, using m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester (SMBS). The Moringa oleifera Coagulant Protein (MOCP) from a seed extract was employed for its characteristic coagulation activity. The performance of the MOCP functionalized microspheres was evaluated as a function of turbidity removal of problematic colloidal clay from water via magnetic separation, resulting in over 80% of activity within 15 min. Surface of these hybrid materials can be re-generated by treatment with alcohol, allowing their easy magnetic separation and re-use. The rapid and strong response with tunable magnetic property makes these hybrid microspheres a powerful tool for many potential applications, due to the general applicability of the developed methodology.

Simultaneous acquisition of Fe3O4 monocrystals: Tunable magnetic properties with various morphologies

Fe3O4 nanoparticles (NPs) with a face-centered cubic (fcc) structure and two different morphologies (nanospheres and nanoprisms) were synthesized by a facile one-step method. The synthesized Fe3O4 nanospheres and nanoprisms were monocrystalline and separable in a magnetic field. In different volume ratios of oleylamine (OAm) to dibenzyl ether, the sizes of the prepared Fe3O4 NPs ranged from 5 to 21 nm. The OAm amount in the synthesis can significantly control the morphology of Fe3O4 NPs. As the OAm content increased from 10 ml to 30 ml, the faceted nanoprisms shrank while the nanospheres enlarged. At an OAm content of 25 ml, the nanoprisms diminished while more hexagonal and sphere-like particles appeared, implying a critical point of morphology transition from triangle to hexagon. The magnetic properties also depended on the NP morphology and size. The prepared Fe3O4 NPs are promising candidates in medical applications such as magnetic resonance imaging, targeted drug delivery, blood purification, and tumor hyperthermia.

Tunable electronic and magnetic properties of substitutionally doped graphene

Abstract The van der Waals materials provide a playground to study new phenomena in two-dimensional magnetism. Here, we discuss the possibility of induction of a magnetic state in graphene by modifying its band structure by substitutional doping. Based on a density-functional theory we study the structural, electronic and magnetic properties of graphene doped with V, Cr, Mn, Fe, Co, Ni, and Cu atoms. It was observed that substitutionally doping, strongly influences the structural as well as the electronic properties of the resulting layers. Our study identified four candidates (graphene doped with V, Cr, Fe, and Co atoms) whose ferromagnetic order is energetically the most favorable. In the case of V- and Cr-doped graphene, Curie temperatures obtained analytically far exceed the room temperature. Furthermore, the Mn-doped system prefers antiferromagnetic order and in the case of Ni and Cu dopants, we observed nonmagnetic behavior. Although the addition of the Hubbard parameter U slightly modified the magnetic properties the graphene sheets doped with V and Cr atoms are found to have the high Curie temperature ( ∼ 500-800 K). Our studies demonstrate, that the obtained results can be valuable in designing nanodevices for applications.

Theoretical study of strain induced magnetic transition of single-layer CrTe3

Developing novel controllable two-dimensional semiconductor materials is crucial to thin film spintronic devices, which may lead to a revolution of information devices. Recently, the easily cleavable CrTe3 has attracted much attention for studying the magnetic properties of two-dimensional materials. In this paper, we have demonstrated theoretically that an elastic tensile strain can turn the antiferromagnetic coupled single-layer CrTe3 (SL-CrTe3) into a ferromagnetic (FM) system, favoring its potential application in thin film spintronic devices. The FM SL-CrTe3 undergoes a further transition from a semiconductor to a metal under a biaxial tensile strain of 9%. The kinetic stability of SL-CrTe3 under 10% tensile strain is verified by a molecular dynamics simulation at room temperature. We suppose that the strain-dependent magnetic behaviors of SL-CrTe3 resulted from the competition between superexchange and direct interactions. The tunable magnetic and electronic properties of SL-CrTe3 imply immense potential in spintronic device applications.

Magnetic and conducting composites of cobalt ferrite nanorods in a polyaniline matrix

Composites of cobalt ferrite nanorods in a polyaniline matrix have been synthesized and characterized by electron microscopy observation, X‐ray diffraction, infrared spectroscopy, thermogravimetric analysis, electrical conductivity, and DC magnetization measurements. The composites were prepared using dodecylbenzenesulphonic acid both as a particle protector and as acid media. In the magnetic experiments, hysteresis loops were observed, revealing ferromagnetism for both particles and composites. The results indicate that the magnetic properties of the particles were preserved in the composites, and on the other hand, the conductivity was almost independent on the polymer/particle ratio. These composites are new materials that show easily tunable magnetic properties, and are expected to be candidates for applications such as microwave shields. POLYM. ENG. SCI., 60:597–606, 2020. © 2020 Society of Plastics Engineers

From Ni–P Metastable Alloy Nanoparticles to Bulk Submicrometer Grain-Sized MMCs with Tunable Mechanical and Magnetic Properties

In this study, submicrometer grain-sized metal matrix composites (MMCs) based on nickel were elaborated via a bottom-up strategy combining the polyol process and a non-conventional heat treatment route. First, four sets of nano-sized Ni–P metastable alloy nanopowders with an average particle size centered at 50, 100, 130, and 220 nm were prepared by the polyol process modified by the addition of hypophosphite (strong reducing agent) and heterogeneous nucleation using silver nitrate and platinum salt (nucleating agents). The heat treatment step was realized by reactive spark plasma sintering (R-SPS) at identical heat treatment conditions (600 °C, 53 MPa, and 10 min as holding time). R-SPS transformed the Ni–P metastable alloys into bulk submicrometer grain-sized MMCs with Ni as the matrix and Ni3P as the reinforcement. Mechanical and magnetic properties of the four MMC samples were found to be closely related to the grain size of the Ni matrix, which varied from 247 to 638 nm. Yield stress, maximum stress, and coercive field increased when the grain size decreased, while plastic strain and magnetization saturation decreased. The reinforcement Ni3P phase enhanced the mechanical characteristics of the composite. Crossover behavior was observed at around 350 nm Ni grain size, where a ductile and soft magnetic composite was tuned into a hard mechanical and semi-hard magnetic one.

Tunable physical properties in BiAl1-x Mn x O3 thin films with novel layered supercell structures.

Morphological control in oxide nanocomposites presents enormous opportunities for tailoring the physical properties. Here, we demonstrate the strong tunability of the magnetic and optical properties of Bi-based layered supercell (LSC) multiferroic structures, i.e., BiAl1−xMnxO3, by varying the Al : Mn molar ratio. The microstructure of the LSC structure evolves from a supercell structure to Al-rich pillars in the supercell structure as the Al molar ratio increases. The LSC structures present excellent multiferroic properties with preferred in-plane magnetic anisotropy, a tunable band gap and anisotropic dielectric permittivity, all attributed to the microstructure evolution and their anisotropic microstructure. Three different strain relaxation mechanisms are identified that are active during thin film growth. This study provides opportunities for microstructure and physical property tuning which can also be explored in other Bi-based LSC materials with tailorable multiferroic and optical properties.

The tunable electric and magnetic properties of 2D MXenes and their potential applications

This review paper is focused on the electrical and magnetic property based applications of MXenes such as cancer theranostics, spintronics, and shielding against electromagnetic pollution.

Simultaneously tunable luminescence and magnetic properties in bifunctional NaYF4: Yb3+/Er3+ microcrystals

Simultaneously tunable luminescence and magnetic properties in bifunctional NaYF4: Yb3+/Er3+ microcrystals

Simultaneously tunable luminescence and magnetic properties in bifunctional NaYF4: Yb3+/Er3+ microcrystals

Simultaneously tunable luminescence and magnetic properties in bifunctional NaYF4: Yb3+/Er3+ microcrystals

Co-Pt bimetallic nanoparticles with tunable magnetic and electrocatalytic properties prepared by atomic layer deposition.

Co-Pt bimetallic nanoparticles with adjustable composition and particle size were prepared by the combination of atomic layer deposition and H2 post-deposition annealing. The structure, magnetic and electrocatalytic properties of Co-Pt bimetallic nanoparticles can be facilely tuned by controlling the composition.

Electronic structure, magnetic anisotropy and Dzyaloshinskii-Moriya interaction in Janus Cr2I3X3 (X = Br, Cl) bilayers.

Two-dimensional (2D) layers with a tunable electronic structure and magnetic properties have attracted much attention due to their unique characteristics and practical applications. Here, the electronic structure and magnetic properties of the 2D van der Waals Cr2I3X3 (X = Br, Cl) bilayers are investigated systematically by first-principles calculations. The Cr2I3X3 bilayers show the stacking-dependent magnetic ground state, where the band gap can be effectively tailored by the stacking and combination modes. In the Cr2I3Br3 (Cr2I3Cl3) bilayers, the electrostatic potential and electric polarization can be greatly affected by combination modes, which can be attributed to the parallel or antiparallel built-in electric fields between the monolayers. The Cr2I3X3 bilayers show a perpendicular magnetic anisotropy. The magnetic anisotropy energy of the Cr2I3Cl3 bilayer is larger than that of the Cr2I3Br3 bilayer, which can be attributed to the enhanced contribution of the hybridized I px and py orbitals of the Cr2I3Cl3 bilayer. Additionally, the Dzyaloshinskii-Moriya interaction of the Cr2I3Br3 bilayer can also be modulated by the combination modes. These results can boost the development of Janus 2D materials, which are useful in the design of multifunctional spintronic devices.

Control of C3N4and C4N3carbon nitride nanosheets’ electronic and magnetic properties through embedded atoms

In the present work, the effect of various embedded atom impurities on tuning electronic and magnetic properties of C3N4 and C4N3 nanosheets have been studied using first-principles calculations. Our calculations show that C3N4 is a semiconductor and it exhibits extraordinary electronic properties such as dilute-magnetic semiconductor (with H, F, Cl, Be, V, Fe and Co); metal (with N, P, Mg and Ca), half-metal (with Li, Na, K, Al, Sc, Cr, Mn, and Cu) and semiconductor (with O, S, B, C, Si, Ti, Ni and Zn) with the band gaps in the range of 0.3-2.0 eV depending on the species of embedded atom. The calculated electronic properties reveal that C4N3 is a half-metal and it retains half-metallic character with embedded H, O, S, F, B, N, P, Be, Mg, Al, Sc, V, Fe, Ni and Zn atoms. The substitution of Cl, C, Cr and Mn atoms create ferromagnetic-metal character in the C4N3 nanosheet, embedded Co and Cu atoms exhibit a dilute-magnetic semiconductor nature, and embedded Ti atoms result in the system becoming a semiconductor. Therefore, our results reveal the fact that the band gap and magnetism can be modified or induced by various atom impurities, thus, offering effective possibilities to tune the electronic and magnetic properties of C3N4 and C4N3 nanosheets.

Composition assisted tuning properties of CoCrxFe2-xO4 spinel nano ferrites

Structural, magnetic properties, bandgap of sol gel auto-combustion synthesized single phase CoCrxFe2-xO4 (x = 0.0–1.0) nano ferrites, were studied by x-ray diffraction, vibration sample magnetometer, ultra violet visible spectroscopy. Linear decrease of lattice parameter with increasing Cr-content is ascribed to difference between ionic radii of Cr3+ (0.064 nm), Fe3+ (0.067 nm). Linear decrease of grain diameter with increasing Cr-content, shows presence of Cr in spinel lattice which hinders grain growth. Results show bandgap tenability; reveal that Cr-addition is effective in determining coercivity, saturation magnetization of studied samples. Results illustrate effectiveness of compositional variation for structural modification, leads to tuning of magnetic properties, bandgap.

Tunable electronic structure and magnetic properties of Mn–NM (NM = B, C, N and S) co-doped monolayer WSe2

Searching two-dimensional (2D) magnetic materials with high spin polarization is important for the development and application of next-generation spintronic devices. Here, based on spin-polarized density functional theory calculations, the stability, electronic structure and magnetic properties of Mn-doped and Mn–NM (NM = B, C, N and S) co-doped monolayer WSe2 are investigated in detail. The results indicate that the Mn–S co-doped MoSe2 configuration has the lowest formation energy in the whole chemical potential range and easily spontaneously forms under thermodynamic equilibrium conditions. Obviously, the Mn-doped WSe2 configuration exhibits magnetic half-metallicity characters with a completely spin polarization at the Femi level [Formula: see text], which can be attributed to that the electrons partially occupy the bonding states consisting of Mn [Formula: see text] states at the [Formula: see text]. For the Mn–C and Mn–S co-doped configurations, the Mn [Formula: see text] and [Formula: see text] orbitals strongly hybridize with the C or S spin-up [Formula: see text] orbital at the [Formula: see text], which induces strong spin exchange splitting and eventually gives rise to the magnetic semiconductor character. However, the Mn–B and Mn–N co-doped configurations exhibit completely symmetrical spin-up and spin-down channel of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] states due to the effective charge compensation between Mn and B or N atoms. These studies provide a new class of 2D magnetic materials for future spintronics devices.

The Potential Biomedical Application of NiCu Magnetic Nanoparticles

Magnetic nanoparticles became increasingly interesting in recent years as a result of their tailorable size-dependent properties, which enable their use in a wide range of applications. One of their emerging applications is biomedicine; in particular, bimetallic nickel/copper magnetic nanoparticles (NiCu MNPs) are gaining momentum as a consequence of their unique properties that are suitable for biomedicine. These characteristics include stability in various chemical environments, proven biocompatibility with various cell types, and tunable magnetic properties that can be adjusted by changing synthesis parameters. Despite the obvious potential of NiCu MNPs for biomedical applications, the general interest in their use for this purpose is rather low. Nevertheless, the steadily increasing annual number of related papers shows that increasingly more researchers in the biomedical field are studying this interesting formulation. As with other MNPs, NiCu-based formulations were examined for their application in magnetic hyperthermia (MH) as one of their main potential uses in clinics. MH is a treatment method in which cancer tissue is selectively heated through the localization of MNPs at the target site in an alternating magnetic field (AMF). This heating destroys cancer cells only since they are less equipped to withstand temperatures above 43 °C, whereas this temperature is not critical for healthy tissue. Superparamagnetic particles (e.g., NiCu MNPs) generate heat by relaxation losses under an AMF. In addition to MH in cancer treatment, which might be their most beneficial potential use in biomedicine, the properties of NiCu MNPs can be leveraged for several other applications, such as controlled drug delivery and prolonged localization at a desired target site in the body. After a short introduction that covers the general properties of NiCu MNPs, this review explores different synthesis methods, along with their main advantages and disadvantages, potential surface modification approaches, and their potential in biomedical applications, such as MH, multimodal cancer therapy, MH implants, antibacterial activity, and dentistry.

Graphene-like BC6N single-layer: Tunable electronic and magnetic properties via thickness, gating, topological defects, and adatom/molecule

Abstract By using density functional theory-based first-principles calculations, we investigate the structural, electronic, optical, and transport properties of pristine single-layer BC6N. Under different external actions and functionalization. Increasing the thickness of the structure results in a decrease of the band gap. Applying a perpendicular electric field decreases the band gap and a semiconductor-to-topological insulator transition is revealed. Uniaxial and biaxial strains of +8% result in a semiconductor-to-metal transition. Nanoribbons of BC6N having zigzag edge with even (odd) values of widths, become metal (semiconductor), while the armchair edge nanoribbons exhibit robust semiconducting behavior. In addition, we systematically investigate the effect of surface adatom and molecule, substitutional impurity and defect engineering on the electronic properties of single-layer BC6N and found transitions from metal to half-metal, to ferromagnetic metal, to dilute magnetic semiconductor, and even to spin-glass semiconductor. Furthermore we found that, topological defects including vacancies and Stone–Wales type, induce magnetism in single-layer BC6N.

Structure, optical and magnetic properties of new Bi0.5Na0.5TiO3- SrMnO3\u2212\u03b4 solid solution materials

The new Bi0.5Na0.5TiO3-SrMnO3−δ solid solution materials were fabricated via sol–gel method. The random incorporation of Sr and Mn cations into host lattice of Bi0.5Na0.5TiO3 resulted in structural distortion and influenced on the reduction of the optical band gap from 3.07 eV to 1.81 eV for pure Bi0.5Na0.5TiO3 and 9 mol% SrMnO3−δ solid solution into Bi0.5Na0.5TiO3. The magnetic properties of Bi0.5Na0.5TiO3 materials at room temperature were tuned via compensation of diamagnetic material with weak-ferromagnetism to ferromagnetism with low SrMnO3−δ content and combination of paramagnetism/antiferromagnetism-like and ferromagnetism with higher SrMnO3−δ content solid solution in Bi0.5Na0.5TiO3. The tunable magnetic and optical properties of lead-free ferroelectric materials was promising for their application to green electronic devices.

The effects of annealing temperature and heating rate on Ta/TbFeCo bilayers

Among various perpendicularly anisotropic magnetic materials, amorphous rare earth-transition metal RE-TM alloys have attracted much interest due to the advantages of tunable magnetic properties and suitable perpendicular magnetic anisotropy (PMA) strength. In this study, the magnetic properties of the Ta/TbFeCo/MgO structure with various Tb-contents are investigated under different annealing conditions like heating rate and annealing temperature. The samples were annealed at heating rate from 10 °C/min to 50 °C/min and holding time was varied from 10 min to 30 min with annealing temperatures ranging from 100 to 150 °C. We found that fast heating rate and low holding temperature help to improve PMA and significantly increase the saturation magnetization and squareness of the TbFeCo films.