Ferromagnetic Oxide Research Articles

Co‐immobilization of multiple enzymes on ferromagnetic nanoparticles for the depolymerization of xyloglucan

AbstractXyloglucan (XG) is an abundant polysaccharide in plant cell walls and some seeds and requires at least four different enzymes for complete depolymerization. Recombinant xyloglucanase from Aspergillus niveus (XegA), α‐xylosidase from Escherichia coli (YicI), β‐galactosidase from Hypocrea jecorina (Bga1) and β‐glucosidase from H. jecorina (Bgl1) were covalently immobilized individually and in combination on chitosan‐coated ferromagnetic iron oxide nanoparticles functionalized with glutaraldehyde. All immobilized enzymes presented reduced specific catalytic activity, where immobilized YicI, XegA, Bga1 and Bgl1 retained 14.9, 76.9, 29.5 and 6.6% activity as compared with the free enzymes, respectively. Immobilized and free enzymes presented similar optimum catalytic pH and optimum catalytic temperatures differed by ±10°C between the free and immobilized enzymes. Bga1 and Bgl1 presented decreased maximum catalytic temperatures (Topt), while YicI presented an increased Topt. The Topt of XegA remained unaltered. Mass spectrometry confirmed that nanoparticles carrying all four co‐immobilized enzymes degraded XG to glucose, galactose and xylose, and higher proportions of co‐immobilized Bgl1 and XegA resulted in higher XG saccharification. Although levels of Bgl1 activity were limiting, five re‐use cycles of the co‐immobilized enzymes were demonstrated, providing proof‐of‐principle for the use of a four‐component multienzyme nanoparticle in the breakdown of a complex polysaccharide. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Tunnel Spin-Polarization of Ferromagnetic Metals and Ferrimagnetic Oxides and Its Effect on Tunnel Magnetoresistance

This work presents an examination and unification of fragmented data on spin polarization in half-metallic, ferrimagnetic oxides. It also includes well understood ferromagnetic metals for comparison. The temperature and disorder dependencies of the spin polarization are evaluated. Both the temperature dependence of the tunnel magnetoresistance and, for the very first time, its temperature coefficient are calculated based on the simplified Julliére model. The tunnel magnetoresistance in the magnetic tunnel junctions deteriorates due to the temperature dependence of the spin polarization the lower the Curie temperature is. As a result, magnetic tunnel junctions—consisting of ferromagnetic oxides with a Curie temperature not far above room temperature—are not promising for room temperature applications. Additionally, ferrimagnetic oxides possessing a Curie temperature below 650 K are not suitable for room temperature applications because of an unacceptable temperature coefficient exceeding −2%.

Synthesis and application of ferromagnetic graphene oxide nanocomposite as an effective adsorbent for Clonazepam: Batch experiments, modeling, regeneration, and phytotoxicity

In this work, a ferromagnetic graphene oxide nanocomposite (mGO) was produced, characterized, and tested for clonazepam removal from water. After the nanocomposite production and characterization, adsorption tests showed that the initial pH does not influence the clonazepam removal. Clonazepam adsorption onto mGO was an extremely fast process, with equilibrium reached within the first minutes. Sips isotherm showed the best fit to the experimental data, presenting a maximum adsorption capacity of 14.81 mg g−1, indicating that the clonazepam adsorption process is favorable. Pseudo-first order was the empirical kinetic model that best fit the experimental data, with R2 > 0.99; as for the phenomenological models, both the Linear and Quadratic Driving Force models fit the data with R2 > 0.97. Moreover, the regenerative and reuse potential of the nanocomposite was analyzed, exhibiting remarkable regeneration potential, even after 5 adsorption/desorption cycles. Finally, according to the phytotoxicity tests, it was observed that the effluent treated with mGO did not present toxicity to watercress seeds, as all seeds germinated. This work stands out because it proposes a nanoparticle composite material for the viable, efficient, eco-friendly, and easy removal of an emerging contaminant from water.

High-Efficiency Magnon-Mediated Magnetization Switching in All-Oxide Heterostructures with Perpendicular Magnetic Anisotropy.

The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron-mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all-oxide heterostructures of SrRuO3 /NiO/SrIrO3 are epitaxially grown on SrTiO3 single-crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO3 with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO3 with strong spin-orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion-related energy dissipation from electron-mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all-oxide spintronic devices operated by magnon current.

Electron-beam-evaporation-based multi-source oxide MBE as a synthesis method for high-quality and novel magnetic materials—beyond 3d transition metal compounds

Magnetism and magnetic materials are among the most extensively studied research topics in condensed matter physics. While many practical applications of magnetic materials have been already launched, including permanent magnet motors, magnetic heads in hard disc drives (HDDs), and magnetoresistive random access memories (MRAMs), further search for new magnetic materials has not lost its charm. Here, we show that a multi-electron gun MBE apparatus for oxides, equipped with a high precision rate control system enables the synthesis of well-known ferromagnetic oxides, e.g., SrRuO3 of unparalleled quality. Furthermore, this method also allows to fetch novel magnetic materials, e.g., Sr3OsO6, that are well outside of the synthesis conditions known from 3d transition metal oxides.

Self-Confirming Magnetosomes for Tumor-Targeted T1 /T2 Dual-Mode MRI and MRI-Guided Photothermal Therapy.

Nanomaterials as T1 /T2 dual-mode magnetic resonance imaging (MRI) contrast agents have great potential in improving the accuracy of tumor diagnosis. Applications of such materials, however, are limited by the complicated chemical synthesis process and potential biosafety issues. In this study, the biosynthesis of manganese (Mn)-doped magnetosomes (MagMn) that not only can be used in T1 /T2 dual-mode MR imaging with self-confirmation for tumor detection, but also improve the photothermal conversion efficiency for MRI-guided photothermal therapy (PTT) is reported. The MagMn nanoparticles (NPs) are naturally produced through the biomineralization of magnetotactic bacteria by doping Mn into the ferromagnetic iron oxide crystals. In vitro and in vivo studies demonstrated that targeting peptides functionalized MagMn enhanced both T1 and T2 MRI signals in tumor tissue and significantly inhibited tumor growth by the further MRI-guided PTT. It is envisioned that the biosynthesized multifunctional MagMn nanoplatform may serve as a potential theranostic agent for cancer diagnosis and treatment.

Enhanced Magnetoresistance Effect in Graphene Coupled to a Ferromagnetic Oxide with Charge Orbital Ordering

In this paper, we fabricated graphene/Fe3O4 heterostructure devices by stacking monolayer graphene on magnetite (Fe3O4) substrate and investigated their magneto-transport properties. Interestingly, graphene/Fe3O4 heterostructure devices exhibit a giant magnetoresistance (MR) of 70% at a low magnetic field of 0.65[Formula: see text]T and at 11[Formula: see text]K, which is three times greater than that of graphene on SiO2. Based on standard two-fluid model and LDA[Formula: see text]U simulation, we showed that the observed enhanced MR effect is due to the increased disorder in graphene induced through the charge polarization via the alignment of C atoms of graphene over the charge ordered B-site cations of Fe3O4. Our results demonstrate a potential way to enhance graphene MR effect through coupling graphene with a suitable substrate with charge orbital ordering.

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 (BITCx/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co2+ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITCx/LSMO composite thin films was investigated. Co2+ doping induces improved ferroelectricity and weak ferromagnetism for the BITCx phase. Especially, the single-phase BITC0.05 film exhibits a maximum ME voltage coefficient (αE) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ϵr, minimum tanδ, highest remnant polarization of 24.2 μC/cm2, lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum aE value of 27.3 V/cm·Oe. Based on these findings, Co2+-doped Bi4Ti3O12 has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi4Ti3O12 with ferromagnetic oxides benefits the improvement of ME composite thin films.

Observation of topological Hall torque exerted on a domain wall in the ferromagnetic oxide SrRuO3.

In a ferromagnetic Weyl metal SrRuO3, a large effective magnetic field Heff exerted on a magnetic domain wall (DW) by current has been reported. We show that the ratio of Heff to current density exhibits nonmonotonic temperature dependence and surpasses those of conventional spin-transfer torques and spin-orbit torques. This enhancement is described well by topological Hall torque (THT), which is exerted on a DW by Weyl electrons emerging around Weyl points when an electric field is applied across the DW. The ratio of the Heff arising from the THT to current density is over one order of magnitude higher than that originating from spin-transfer torques and spin-orbit torques reported in metallic systems, showing that the THT may provide a better way for energy-efficient manipulation of magnetization in spintronics devices.

Ferromagnetic Vortex Iron Oxide Nanorings Modified with Integrin β1 Antibody for Targeted MRI Tracking of Human Mesenchymal Stem Cells.

Mesenchymal stem cells (MSCs) have demonstrated great potential for tissue engineering and regenerative medicine applications. Noninvasive and real-term tracking of transplanted MSCs in vivo is crucial for studying the distribution and migration of MSCs, and their role in tissue injury repair. This study reports on the use of ferrimagnetic vortex iron oxide (FVIO) nanorings modified with anti-human integrin β1 for specific recognition and magnetic resonance imaging (MRI) tracking of human MSCs (hMSCs). Integrin β1 is highly expressed at all stem cell proliferation and differentiation stages. Therefore, the anti-integrin β1 antibody (Ab) introduced in FVIO targets integrin β1, thus enabling FVIO to target stem cells at any stage. This is unlike the traditional MRI-based monitoring of transplanted stem cells, which usually requires pre-labeling the stem cells with tracers before injection. Because of the ability to recognize hMSCs, the Ab-modified FVIO nanotracers (FVIO-Ab) have the advantage of not requiring pre-labeling before stem cell transplantation. Furthermore, the FVIO-Ab nanotracers have high T*₂ contrast resulting from the unique magnetic properties of FVIO which can improve the MRI tracking efficiency of stem cells. This work may provide a new way for stem cell labeling and in vivo MRI tracking, thus reducing the risks associated with stem cell transplantation and promoting clinical translation.

New half-metallic ferromagnetic oxides XBe3O4 (X=Li and Na)

The paper presents the results of the structural, electronic, magnetic, and mechanical stabilities of XBe3O4 (X = Li, Na, and K) with the space group Pm3 m, obtained by Density Functional Theory within the frame work of the Full-Potential Linearized Augmented Plane Waves method. The compounds are energetically stable in their ferromagnetic phase, while only LiBe3O4 and NaBe3O4 are mechanically stable. Both stable ones are ductile and anisotropic. The calculated spin-polarized band structures and densities of states show the half-metallic nature, with gap [half-metallic gap] of 7.73 eV [0.18 eV] and 5.57 eV [0.28 eV] for LiBe3O4 and NaBe3O4 compounds, respectively. The total magnetic moment is 1.0 μB for both systems, confirming their half-metallicity. The estimated Curie temperatures are 403.5 K and 422.9 K for LiBe3O4 and NaBe3O4 compounds, respectively. The obtained properties, such as 100% spin-polarization and high Curie temperature, required in technologies for fabricating materials for spintronic devices, make LiBe3O4 and NaBe3O4 as good candidates for these applications.

Spin‐Glass State above Room Temperature in a Layered Nickelate Lan+1NinO3n+1

AbstractOxide interfaces provide a fertile ground for new forms of magnetic textures that arise from different symmetry constraints, proximity effects, and charge transfer. Here, a room‐temperature spin glass state stabilized in heterostructures of the ferromagnetic metallic oxide La2/3Sr1/3MnO3 (LSMO) and the layered Lan+1NinO3n+1 (L‐LNO) is reported. Electron energy loss spectra and depth‐profile X‐ray photoelectron spectroscopy reveal the interfacial electron transfer from Mn3+ to localized Ni3+ states. Density functional theory calculations indicate that charge transfer drives the enhancement of ferromagnetic exchange interaction in the nickelate, leading to the formation of local magnetic order. The room temperature spin‐glass state in this artificially engineered LSMO/L‐LNO bilayer structure affords opportunities for designing emergent topological spin textures and spintronic devices.

Hard x-ray photoelectron spectroscopy of tunable oxide interfaces

The tunability of the oxygen content in complex oxides and heterostructures has emerged as a key to designing their physical functionalities. Controlling the interface reactivity by redox reactions provides a powerful means to deliberately set distinct oxide phases and emerging properties. We present routes on how to control oxygen-driven redox mechanisms in ultrathin ferro(i)magnetic and ferroelectric oxide films and across oxide interfaces. We address the growth and control of metastable EuO oxide phases, the control of phase transitions of binary Fe oxides by oxygen migration, the in operando determination of NiFe2O4/SrTiO3 interface band alignments, as well as the role of interfacial oxide exchange in ferroelectric HfO 2-based capacitors—uncovered by the unique capabilities of photoelectron spectroscopy and, in particular, using hard x-rays.

Luminescent magnets: hybrid supraparticles of a lanthanide-based MOF and ferromagnetic iron oxide by assembly in a droplet via spray-drying

Herein, we report on the successful creation of a luminescent micron-sized magnet.

Observation of room temperature d0 ferromagnetism, band-gap widening, zero dielectric loss and conductivity enhancement in Mg doped TiO2 (rutile + anatase) compounds for spintronics applications

Recently, non-magnetic element doped d0 ferromagnetic oxides have been widely studied for their potential spintronics applications. Crystal Structure, elemental color mapping, magnetic, electrical and optical properties of Ti1-xMgxO2 (x ​= ​0, 0.03, 0.06, 0.09 and 0.12) compounds, synthesized by solid-state route were systematically investigated in this paper. X-ray diffraction patterns of these compounds reveal that all Mg-doped TiO2 have been formed in mixed phase of rutile (predominant) and anatase. The anatase phase increases with the increase of the Mg doping concentration. The elemental color mapping using energy dispersive spectroscopy indicates that all elements such as Ti and Mg are distributed uniformly throughout the sample. Ferromagnetism with hysteresis loops is seen in all the compounds, with Curie temperatures above 400 ​K and coercivity values in the range 380–790 ​Oe. The maximum value of saturation magnetization was exhibited by the 6% doped sample. Zero field cooled and field cooled magnetization curves show a bifurcation, which pertains to magnetic irreversibility. The optical band gap of these compounds widens up to 9% of Mg doping and thereafter narrows on further doping. Moreover, these materials show zero loss tangent and an enhancement of dielectric constant with Mg doping. These materials may be useful in magnetic storage, spintronics and optoelectronics applications at high frequency.

Silica Coating of Ferromagnetic Iron Oxide Magnetic Nanoparticles Significantly Enhances Their Hyperthermia Performances for Efficiently Inducing Cancer Cells Death In Vitro.

Increasing the biocompatibility, cellular uptake, and magnetic heating performance of ferromagnetic iron-oxide magnetic nanoparticles (F-MNPs) is clearly required to efficiently induce apoptosis of cancer cells by magnetic hyperthermia (MH). Thus, F-MNPs were coated with silica layers of different thicknesses via a reverse microemulsion method, and their morphological, structural, and magnetic properties were evaluated by multiple techniques. The presence of a SiO2 layer significantly increased the colloidal stability of F-MNPs, which also enhanced their heating performance in water with almost 1000 W/gFe as compared to bare F-MNPs. The silica-coated F-MNPs exhibited biocompatibility of up to 250 μg/cm2 as assessed by Alamar Blues and Neutral Red assays on two cancer cell lines and one normal cell line. The cancer cells were found to internalize a higher quantity of silica-coated F-MNPs, in large endosomes, dispersed in the cytoplasm or inside lysosomes, and hence were more sensitive to in vitro MH treatment compared to the normal ones. Cellular death of more than 50% of the malignant cells was reached starting at a dose of 31.25 μg/cm2 and an amplitude of alternating magnetic field of 30 kA/m at 355 kHz.

Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case.

Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMn2O4 films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMn2O4 films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMn2O4 film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMn2O4 thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.

Propagation of ultrasonic wave in magnetic Pickering emulsion under DC magnetic field

A Pickering emulsion is an emulsion stabilized by solid particles accumulated at the surface of droplets. It is also possible to create a stable Pickering emulsion stabilized by ferromagnetic iron oxide nanoparticles to make it susceptible to magnetic fields. This type of emulsion has received great research interest in recent years because it has generated and holds the promise of a variety of practical applications. One interesting application is magnetic separation in the gradient magnetic field. However, the real-time characterization of magnetic Pickering emulsions, especially under external stimuli such as magnetic fields, is generally challenging. We used a convenient method to control the properties of magnetic particle-stabilized emulsions via the ultrasound technique. In the experiments, we investigated the attenuation of ultrasound using ultrasonic spectroscopy as a function of the magnetic particle concentration and magnetic field intensity. The analysis of ultrasonic waves as a function of frequency provided information about the movement of magnetic Pickering droplets during magnetic separation. The results showed much weaker separation for a low magnetic particles concentration as the magnetic force was not sufficient to induce significant droplets movement, whereas for a high concentration the magnetic separation occurred very dynamically.

Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides

LaxSr2-xNiRuO6, LaxSr4-xNiRuO8, and LaxSr3-xNiRuO7 are, respectively, the n = ∞, 1, and 2 members of the (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n+1 compositional series. Reaction with CaH2, in the case of the LaxSr2-xNiRuO6 perovskite phases, or Zr oxygen getters in the case of the LaxSr4-xNiRuO8 and LaxSr3-xNiRuO7 Ruddlesden-Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n-1 compounds (LaxSr2-xNiRuO4, LaxSr4-xNiRuO6, and LaxSr3-xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+ and Ru2+ centers they contain. Increasing the La3+ concentration (x > 1) leads to a reduction of some of the Ru2+ centers to Ru1+ centers and a suppression of the ferromagnetic state (lower Tc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+ concentration (x < 1) oxidizes some of the Ru2+ centers to Ru3+ centers and enhances the ferromagnetic coupling (increased Tc, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.

Bioconvection in Magneto Hydrodynamics Casson Nanoliquid (Fe3O4-Sodium Alginate) With Gyrotactic Microorganisms Over an Exponential Stretching Sheet

The present investigation focuses on the influence of motile gyrotactic microorganisms and thermal heat flux on three-dimensional convective flow of a Casson nanoliquid over an elongated surface. The flow equations are modelled by using Tiwari-Das nanofluid model. Sodium alginate (SA) is considered as the base fluid together with Ferromagnetic oxide (Fe3O4) nanoparticles. The governing flow equations are changed into a system of ODEs with the aid of similarity variables and are then addressed computationally. Influence of various pertinent parameters on different physical quantities is examined graphically. The outcomes of present investigation is validated through comparison study and is found to be in good arrangement. It is noticed that the coefficient of heat transfer rises with growing radiation and Biot numbers. Also the mass transfer coefficient surges for higher values of Schmidt number and generative chemical reaction parameter.