Ferromagnetic Oxide Research Articles

Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide

Magnetic Weyl semimetals have novel transport phenomena related to pairs of Weyl nodes in the band structure. Although the existence of Weyl fermions is expected in various oxides, the evidence of Weyl fermions in oxide materials remains elusive. Here we show direct quantum transport evidence of Weyl fermions in an epitaxial 4d ferromagnetic oxide SrRuO3. We employ machine-learning-assisted molecular beam epitaxy to synthesize SrRuO3 films whose quality is sufficiently high to probe their intrinsic transport properties. Experimental observation of the five transport signatures of Weyl fermions—the linear positive magnetoresistance, chiral-anomaly-induced negative magnetoresistance, π phase shift in a quantum oscillation, light cyclotron mass, and high quantum mobility of about 10,000 cm2V−1s−1—combined with first-principles electronic structure calculations establishes SrRuO3 as a magnetic Weyl semimetal. We also clarify the disorder dependence of the transport of the Weyl fermions, which gives a clear guideline for accessing the topologically nontrivial transport phenomena.

Magnetic Fraction of Fly Ash as a Low-Cost Magnetic Adsorbent for Selective Capture of Phosphoproteins

In the present study, the magnetic fraction of fly ash was separated from the bulk material using a conventional magnet, yielding approximately 50% w/w. As the magnetic fraction of fly ash contains a high content of aluminum oxide, which is recognized as a phosphate adsorbent, and ferromagnetic iron oxides, it is potentially useful as a magnetic solid-phase extraction adsorbent of phosphoproteins. The results showed that the magnetic fraction of fly ash displayed a high enrichment factor of approximately 130-fold as a magnetic solid-phase extraction adsorbent. The phosphoprotein bound-magnetic fraction was efficiently isolated from the sample solution using a conventional magnet. The adsorbent was further applied to the isolation of phosphoproteins from biological samples, i.e., ovalbumin from egg white and caseins from milk. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enrichment of phosphoproteins revealed that the eluted fraction contained more purified phosphoproteins comparing to the initial diluted samples. In addition, the adsorbent may be reused with acceptable adsorption capacity at least three times. The magnetic solid-phase extraction using the magnetic fraction of fly ash as an adsorbent is effective, simple and reusable. Therefore, the magnetic fraction of fly ash may be an alternative low-cost magnetic adsorbent for the sequestration of phosphoproteins from complex samples.

A New Zinc Phosphate-Tellurite Glass for Magneto-Optical Applications.

This work investigates the structural, magnetic and magneto-optical properties of a new zinc phosphate-tellurite glass belonging to the 45ZnO-10Al2O3-40P2O5-5TeO2 system. The glass was prepared by a wet method of processing the starting reagents followed by suitable melting–stirring–quenching–annealing steps. Specific parameters such as density, average molecular mass, molar volume, oxygen packaging density, refractive index, molar refractivity, electronic polarizability, reflection loss, optical transmission, band gap and optical basicity have been reported together with thermal, magnetic and magneto-optical characteristics. Absorption bands appear in the blue and red visible region, while over 600 nm the glass becomes more transparent. FTIR and Raman spectra evidenced phosphate-tellurite vibration modes proving the P2O5 and TeO2 network forming role. Magnetic measurements reveal the diamagnetic character of the Te-doped glass with an additional weak ferromagnetic signal, specific to diluted ferromagnetic oxides. Positive Faraday rotation angle with monotonous decreasing value at increasing wavelength was evidenced from magneto-optical measurements. The final product is a composite material comprising of a non-crystalline vitreous phase and Te-based nanoclusters accompanied by oxygen vacancies. The metallic-like Te colloids are responsible for the dark reddish color of the glass whereas the accompanying oxygen vacancies might be responsible for the weak ferromagnetic signal persisting up to room temperature.

Exchange Bias in a La0.67Sr0.33MnO3/NiO Heterointerface Integrated on a Flexible Mica Substrate.

Flexible electronics integrating spintronics are of great potential in the areas of lightweight and flexible personal electronics. The integration of ferromagnetic and other functional oxides on flexible mica substrates is crucial for the proposed computer technology. In this work, we demonstrate the successful integration of a ferromagnetic-antiferromagnetic nanocomposite of La0.67Sr0.33MnO3 (LSMO)/NiO with unique perpendicular exchange bias properties on a flexible mica substrate. Utilization of multiple sets of buffer layers has been attempted to overcome the large mismatch between the film and the substrate and to achieve high-quality nanocomposite growth on mica. Exchange bias of ∼200 and ∼140 Oe for the applied magnetic field perpendicular and parallel to the film surface, respectively, has been achieved and attributed to the strongly coupled vertical ferromagnetic/antiferromagnetic interfaces. Such nanocomposite thin films exhibit excellent structural robustness and reliability under a cyclic bending test. This work demonstrates the enormous potential of integrating complex two-phase multifunctional oxides on mica for future flexible wearable personal devices.

Underlayer material dependent symmetric and asymmetric behavior of voltage-controlled magnetic anisotropy in CoFeB films

Voltage-controlled magnetic anisotropy (VCMA), observed at the interfaces of ultrathin ferromagnetic metallic films and oxide layer, has proven to be a useful tool for the development of all-electric field controlled spintronics devices. Here, we have studied the symmetric and asymmetric behavior of VCMA in CoFeB/MgO heterostructures, grown on different underlayer materials, by measuring ferromagnetic resonance using spin pumping and inverse spin Hall effect technique. We observe symmetric behavior of VCMA in CoFeB films with Ta underlayer, whereas a systematic transformation from symmetric to asymmetric behavior of VCMA with decreasing CoFeB thickness is observed for Pt underlayer. We speculate that the increased interfacial roughness, defects and strain of ultrathin CoFeB films with Pt buffer layer probably leads to the complicated band structure at CoFeB/MgO interface resulting in asymmetric behavior of VCMA. The observed symmetric behavior of VCMA in control samples justifies the role of interfacial roughness, defects and discards the role of oxide overlayer on the observed asymmetric behavior of VCMA in ultrathin CoFeB films.

Room Temperature Magnetic Memory Effect in Cluster-Glassy Fe-doped NiO Nanoparticles.

The Fe-doped NiO nanoparticles that were synthesized using a co-precipitation method are characterized by enhanced room-temperature ferromagnetic property evident from magnetic measurements. Neutron powder diffraction experiments suggested an increment of the magnetic moment of 3d ions in the nanoparticles as a function of Fe-concentration. The temperature, time, and field-dependent magnetization measurements show that the effect of Fe-doping in NiO has enhanced the intraparticle interactions due to formed defect clusters. The intraparticle interactions are proposed to bring additional magnetic anisotropy energy barriers that affect the overall magnetic moment relaxation process and emerging as room temperature magnetic memory. The outcome of this study is attractive for the future development of the room temperature ferromagnetic oxide system to facilitate the integration of spintronic devices and understanding of their fundamental physics.

Molecular modeling analyses for graphene functionalized with Fe3O4 and NiO

Graphene has attracted great concern in recent years as one of the potential 2D materials in various applications. This work is devoted for assessing the feasibility of functionalizing 2D graphene sheets with ferromagnetic and antiferromagnetic metal oxides namely magnetite (Fe3O4) and nickel oxide (NiO). Molecular models of the proposed candidates are exposed to energy calculations at DFT level, in addition to geometry optimization processes at PM6 method. HOMO/LUMO orbitals, MESP maps and QSAR descriptors are calculated. Results ensure that graphene doped with NiO has the highest reactivity since it possesses the largest TDM and the smallest HOMO/LUMO band gap. MESP maps illustrate that the benzene rings of graphene are most probable to undergo nucleophilic interactions. Addition of Fe3O4 creates new negatively charged active sites that are ready for nucleophilic interactions. The calculated QSAR parameters demonstrate a hydrophobic nature for pure and modified graphene suggesting that they need further modification with further groups for usage in biological applications.

Co-Substitution Effect in Room-Temperature Ferromagnetic Oxide Sr3.1Y0.9Co4O10.5.

We investigated the Co substitution effect for the magnetic properties in room-temperature ferromagnetic oxide Sr3.1Y0.9Co4O10.5. The substituted element (Al and Ga) and low-spin state Co3+, which was changed from a high-spin or intermediate-spin state by Al or Ga substitution, reduced the Curie temperature to even 1.5 times lower than the temperature estimated from a simple dilution effect. Al3+ preferentially substituted for intermediate-spin-state Co3+ in the ferrimagnetic CoO6 layer and deteriorated the saturation magnetization of Sr3.1Y0.9Co4O10.5. By contrast, Ga3+ substituted for high-spin-state Co3+ in the CoO6 layer and/or the antiferromagnetic CoO4.25 layer and enhanced the saturation magnetization per Co ion. These results indicate that the magnetic properties of Sr3.1Y0.9Co4O10.5 can be controlled by selectively substituting for Co3+ with different spin states.

Reactive Oxygen Species Generating Photosynthesized Ferromagnetic Iron Oxide Nanorods as Promising Antileishmanial Agent

Aim: To investigate the photodynamic therapeutic potential of ferromagnetic iron oxide nanorods (FIONs), using Trigonella foenum-graecum as a reducing agent, against Leishmania tropica. Materials & methods: FIONs were characterized using ultraviolet visible spectroscopy, x-ray diffraction and scanning electron microscopy. Results: FIONs showed excellent activity against L. tropica promastigotes and amastigotes (IC50 0.036±0.003 and 0.072±0.001μg/ml, respectively) upon 15min pre-incubation light-emitting diode light (84lm/W) exposure, resulting in reactive oxygen species generation and induction of cell death via apoptosis. FIONs were found to be highly biocompatible with human erythrocytes (LD50 779±21μg/ml) and significantly selective (selectivity index >1000) against murine peritoneal macrophages (CC50 102.7±2.9μg/ml). Conclusion: Due to their noteworthy in vitro antileishmanial properties, FIONs should be further investigated in an in vivo model of the disease.

Iron oxide mineralogy in Mollisols, Aridisols and Entisols from southwestern Pampean region (Argentina) by environmental magnetism approach

Ferromagnetic compounds of seven southwestern soils from Pampean region comprise iron oxides and oxyhydroxides that have an important role, because of their high surface reactivity, controlling soil adsorption and formation/conservation of soil structure among other properties. We detected minutes of iron oxides quantities by selective dissolution techniques: acid oxalate extraction (<12% of the total Fe) and dithionite-citrate-bicarbonate (<44% of the total Fe), moreover, we identified/quantified mixtures of magnetite, maghemite, goethite and hematite minerals by environmental magnetism approach. The magnetic particle size dependent parameters evidence a relationship with extractable Fe oxides, indicating that magnetic particle size distribution on these soils is a relevant property associated to poorly crystalline and free amorphous Fe oxides. In addition, the particle size and SP concentration of ferromagnetic iron oxides are associated with increments of cation exchange capacity and the specific surface area of soil samples. The estimated amounts of hematite are below 2.20 wt%, and lower contents of about 0.25 wt% correspond to magnetite components. Both magnetic iron oxides concentration, as well as the remanent coercivity, increase towards the western region, on the contrary, anhysteretic ratios decrease and hence relatively coarser magnetic particles are dominant in this western region. The present study provides valuable data to characterize Aridisols, Entisols and Mollisols in a region of high fertility that comprises ones of the world’s most productive agricultural soil region.

Study of Induced Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film Grown on (Mg,Sn)3O4 Buffer Layers

We have investigated structural and magnetic properties of cobalt ferrite (CFO)(001) epitaxial thin films grown by RF magnetron sputtering method on (Mg,Sn) 3 O 4 (MSO) buffer layers to induce large perpendicular magnetic anisotropy (PMA) through the magneto-elastic effect. Tuning of the CFO distortion was demonstrated by changing the film thickness of CFO. Torque measurements revealed that a 5-nm thick CFO thin film showed the PMA constant K u = 25.8±1.3 Merg/cm 3 at room temperature, which is extraordinarily large for a ferromagnetic oxide.

Integration of amorphous ferromagnetic oxides with multiferroic materials for room temperature magnetoelectric spintronics

A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe0.66Dy0.24Tb0.1)3O7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-gap (2.4 eV), and a large enough magnetic moment (~200 emu/cc), all of which can be tuned by varying the oxygen content during deposition. Magnetoelectric devices were made by integrating ultrathin FDTO with multiferroic BiFeO3. A strong enhancement in the magnetic coercive field of FDTO grown on BiFeO3 validated a large exchange coupling between them. Additionally, FDTO served as an excellent top electrode for ferroelectric switching in BiFeO3 with no sign of degradation after ~1010 switching cycles. RT magneto-electric coupling was demonstrated by modulating the resistance states of spin-valve structures using electric fields.

Extremely flat surface full granular media with cap layer consisting of high-Ku CoPt grains and ferromagnetic oxide grain boundaries

Investigation of magnetic properties and nanostructure of stacked media with a CoPt-B2O3 granular recording layer (GRL) and granular cap layers (CL) with CoPt and a typical ferromagnetic oxide of rare earth (RE) oxide (RE oxide: Gd2O3, Nd2O3, Sm2O3, and CeO2) are reported. CoPt-RE oxide granular layer shows higher saturation magnetization and magnetic anisotropy than that of CoPtCrB continuous layer. In stacked media with CoPt-Gd2O3 granular CL (9 nm), nucleation field increases from 0.7 to 0.8 kOe and saturation field decreases from 21.5 to 12.5 kOe with comparable values to those of CoPtCrB continuous CL. This indicates that CoPt-RE oxide granular CL is effective to control intergranular exchange coupling. Reduction of coercivity distribution ratio (∆Hc/Hc) from 0.15 to 0.09 which is comparable to that of CoPtCrB continuous CL when CoPt-Gd2O3 granular CL thickness is changed from 4 to 9 nm is observed. This means CoPt-Gd2O3 granular CL is effective to reduce switching field distribution. Furthermore, significant reduction of surface roughness (Ra) for media with CoPt-Gd2O3 granular CL (9 nm) from 0.32 to 0.25 nm is observed. This reveals that CoPt-RE oxide granular CL has a great impact to induce stacked media with flat surface. Based on the cross-section observation by TEM, the media with CoPt-Gd2O3 granular CL shows continuous structure of grain boundaries from the GRL up to the CL and which results in one-on-one growth of magnetic grain with homogeneous columnar structure. Focusing on the surface morphology, media with CoPt-Gd2O3 granular CL shows smoother surface than that of media with CoPtCrB continuous CL which supports the Ra evaluation result. These results indicate that the employment of granular CoPt-RE oxide for CL is not only to reduce switching field distribution but also to flatten surface of the stacked media.

Effect of sintering on morphology and magnetic properties of Fe-Co nano-rods prepared by wet chemical route

Ferromagnetic Fe-Co oxide nano-rods with high coercivity have been synthesized using wet chemical method. Samples were sintered in hydrogen and nitrogen atmosphere at different temperatures. Structural and morphological studies were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) and transmission electron microscopy (TEM) analysis. The magnetic properties of the particles were measured by a vibrating sample magnetometer (VSM) with a varying magnetic field. XRD pattern demonstrates the presence of pure α-Fe phase in the samples sintered in H2 atmosphere while the presence of Co substituted oxide phases in the samples sintered in N2 atmosphere. SEM micrograph of samples sintered in N2 demonstrates the growth of plate like morphology; such growth was not observed when the samples were sintered in H2atmosphere. Non homogeneous growth of nano-rods was obtained when sintered in N2 atm at 550 ºC whereas homogeneous growth was obtained when sintered in N2 atm at 900 ºC. VSM measurement gives the higher amount of coercivity in the samples sintered in N2 which could be attributed to the rod shape of oxide phase which has high L/D ratio and helps in increasing the anisotropy and hence the coercivity. The higher amount of magnetization value than as prepared samples was observed in samples sintered in H2 atmosphere.

Ferromagnetism from non-magnetic ions: Ag-doped ZnO

To develop suitable ferromagnetic oxides with Curie temperature (TC) at or above room temperature for spintronic applications, a great deal of research in doping ZnO with magnetic ions is being carried out over last decade. As the experimental results on magnetic ions doped ZnO are highly confused and controversial, we have investigated ferromagnetism in non-magnetic ion, Ag, doped ZnO. When Ag replaces Zn in ZnO, it adopts 4d9 configuration for Ag2+ which has single unpaired spin and suitable exchange interaction among these spins gives rise to ferromagnetism in ZnO with above room temperature TC. Experimentally, we have observed room temperature ferromagnetism (RTFM) in Ag-doped ZnO with Ag concentration varied from 0.03% to 10.0%. It is shown that zinc vacancy (VZn) enhances the ferromagnetic ordering (FMO) while oxygen vacancy (VO) retards the ferromagnetism in Ag-doped ZnO. Furthermore, the theoretical investigation revealed that VZn along with Ag2+ ions play a pivotal role for RTFM in Ag-doped ZnO. The Ag2+-Ag2+ interaction is ferromagnetic in the same Zn plane whereas anti-ferromagnetic in different Zn planes. The presence of VZn changes the anti-ferromagnetic to ferromagnetic state with a magnetic coupling energy of 37 meV. Finally, it has been established that the overlapping of bound magnetic polarons is responsible for RTFM in low doping concentration. However, anti-ferromagnetic coupling sets in at higher doping concentrations and hence weakens the FMO to a large extent.

Calcination of ytterbia aerogels leads to ferromagnetic nanoporous ytterbium oxide networks

Ytterbium oxide wet gels are synthesized with the dual assistant effects of propylene oxide and citric acid and processed to ytterbium oxide aerogels by supercritical drying. The nanoporous cubic Yb2O3 networks with about 10 nm crystallite size is obtained by heat treatment of ytterbium oxide aerogels in air at 600 °C. The band gap and magnetic property of the nanoporous cubic Yb2O3 networks are analyzed based on the band structure and density of states using first-principles calculation.

Ultralow-Power Orbital-Controlled Magnetization Switching Using a Ferromagnetic Oxide Interface

A major challenge in spintronics is reducing power consumption due to magnetization switching in ferromagnets. Here researchers demonstrate a scheme of orbital-controlled magnetization switching using a ferromagnetic oxide interface. Deterministic, magnetic-field-free 90\ifmmode^\circ\else\textdegree\fi{} magnetization switching is achieved solely by applying an extremely small electric field, and the associated current density is reduced by 8 orders of magnitude, compared to current-driven switching. These results form a basis for a universal strategy for highly efficient magnetization control by band engineering.

Evolution of gluconic acid capped paramagnetic iron oxide nanoparticles

Magnetic iron oxide nanomaterials are essential for many industrial, environmental and biomedical applications. While ferromagnetic and superparamagnetic iron oxide materials are known, paramagnetic iron oxide nanoparticles have not been significantly reported. In this study, we report the synthesis and characterization of the gluconic acid capped paramagnetic iron oxide nanoparticles (PIONs) using a simple green co-precipitation approach. The PIONs were characterized using Fourier Transform infrared spectroscopy, Scanning electron microscopy, X-ray diffractiometry, differential scanning calorimetry, thermogravimetry, Brunauer–Emmett–Teller (BET) and vibrating sample magnetometry (VSM). The material exhibited linear relationship between magnetization and the field, thus confirming its paramagnetic nature. Also, the as-synthesized PIONs showed a positive zeta potential (+29.7 mV), H2 type IV mesoporous characteristics (pore size = 3.09 nm) with a higher surface area (261.31 m2/g) than some materials in the literature. The as-synthesized material, exhibited potentials for catalysis, organic synthesis, adsorption, environmental remediation and magnetic resonance T1 bio-imaging.

Super-Exchange Interaction Induced Overall Optimization in Ferromagnetic Perovskite Oxides Enables Ultrafast Water Oxidation.

Oxygen evolution reaction (OER) is crucial in many renewable electrochemical technologies including regenerative fuel cells, rechargeable metal-air batteries, and water splitting. It is found that abundant active sites with favorable electronic structure and high electrical conductivity play a dominant role in achieving high electrocatalytic efficiency of perovskites, thus efficient strategies need to be designed to generate multiple beneficial factors for OER. Here, highlighted is an unusual super-exchange effect in ferromagnetic perovskite oxide to optimize active sites and enhance electrical conductivity. A systematic exploration about the composition-dependent OER activity in SrCo1 x Rux O3- δ (denoted as SCRx) (x = 0.0-1.0) perovskite is displayed with special attention on the role of super-exchange interaction between high spin (HS) Co3+ and Ru5+ ions. Induced by the unique Co3+ -O-Ru5+ super-exchange interactions, the SCR0.1 is endowed with abundant OER active species including Co3+ /Co4+ , Ru5+ , and O2 2- /O- , high electrical conductivity, and metal-oxygen covalency. Benefiting from these advantageous factors for OER electrocatalysis, the optimized SCR0.1 catalyst exhibits a remarkable activity with a low overpotential of 360 mV at 10 mA cm-2 , which exceeds the benchmark RuO2 and most well-known perovskite oxides reported so far, while maintaining excellent durability. This work provides a new pathway in developing perovskite catalysts for efficient catalysis.

The comparison between superparamagnetic and ferromagnetic iron oxide nanoparticles for cancer nanotherapy in the magnetic resonance system

The paper aims to compare zeta potentials, magnetic properties, electron spin resonance, photoluminescence (PL) spectra and antitumor effect of magneto-mechano-chemically synthesized magneto-sensitive nanocomplexes loaded with the anticancer drug doxorubicin (DOXO) during nanotherapy of Walker-256 carcinosarcoma carried out by a magnetic resonance system. Diamagnetic DOXO acquired the properties of a paramagnetic substance after synthesis. MNC comprising superparamagnetic nanoparticles (NP) and DOXO had different g-factors, zeta potentials, a lower saturation magnetic moment, area of the hysteresis loop, and a higher coercivity compared to similar MNC with ferromagnetic NP. The main PL peak of MNC spectrum was defined by DOXO at 598 nm. MNC composed of superparamagnetic NP and DOXO showed a lower standard deviation of the normal PL spectral distribution than MNC based on ferromagnetic NP in relation to conventional DOXO. MNC containing superparamagnetic NP responded to resonance conditions leading to a more pronounced antitumor effect compared to MNC with ferromagnetic NP in the course of magnetic nanotherapy for Walker-256 carcinosarcoma bearing animals (temperature inside the tumor did not exceed 40 °C). Therefore, these findings are associated with differences in chemotherapeutic effect between MNC due to a different surface charge and conformational changes in DOXO molecules during its magnetoelectric interaction with single- and multidomain NP.