Functional Magnetic Materials Research Articles

Generalized form of the magnetic anisotropy field in micromagnetic and atomistic spin models

We present a general approach to the derivation of the effective anisotropy field which determines the dynamical behaviour of magnetic spins according to the Landau-Lifshitz-Gilbert equation. The approach is based on the gradient in spherical polar coordinates with the final results being expressed in Cartesian coordinates as usually applied in atomistic and micromagnetic model calculations. The approach is generally valid for all orders of anisotropies including higher order combinations of azimuthal and rotational anisotropies often found in functional magnetic materials such as permanent magnets and an emerging class of antiferromagnetic materials with applications in spintronics. Anisotropies are represented in terms of spherical harmonics which have the important property of rational temperature scaling. Effective field vectors are given for anisotropies up to sixth order, presenting a unified framework for implementing higher order magnetic anisotropies in numerical simulations.

Recent progress in the development of RE2TMTM’O6 double perovskite oxides for cryogenic magnetic refrigeration

• The research progress of MCE in RE 2 TMTM ’O 6 DP oxides is reviewed • The magnetism, MTP and magnetocaloric performances are summarized. • Some of the Gd 2 TMTM ’O 6 DP oxides are considerable for cryogenic MR. The magnetic functional materials play a particularly important role in our modern society and daily life. The magnetocaloric effect (MCE) is at the basis of a solid state magnetic refrigeration (MR) technology which may enhance the efficiency of cooling systems, both for room temperature and cryogenic applications. Despite numerous experimental and theoretical MCE studies, commercial MR systems are still at developing stage. Designing magnetic solids with outstanding magnetocaloric performances remains therefore a most urgent task. Herein, recent progresses on characterizing the crystal structure, magnetic properties and cryogenic MCE of rare earths ( RE )-based RE 2 TMTM ’O 6 double perovskite (DP) oxides, where TM and TM ’ are different 3d transition metals, are summarized. Some Gd-based DP oxides are found to exhibit promising cryogenic magnetocaloric performances which make them attractive for active MR applications.

Ultrasonic assisted magnetic solid phase extraction of ultra-trace mercury with ionic liquid functionalized materials

Due to the agglomeration between particles, the inherent adsorption characteristics of magnetic powder materials are usually difficult to fully display. Taking ionic liquid functional materials as an example, the enrichment behavior of these adsorbents for trace mercury (Hg2+) in ultrasonic (US) assisted dispersion mode was systematically studied. The dissociation of protonic ionic liquids (IL) occur in the process of dispersion and the strong electrostatic attraction can improve the diffusion and adhesion of mercury on the adsorbent surface. Spectral measurement data showed that with the help of US, the more uniform dispersion of magnetic materials accelerated the adsorption of trace Hg2+. Ultrasonic intrinsic parameters such as frequency, power and radiation duration significantly affect the dispersion and apparent adsorption properties of magnetic functional materials. In the range of experimental parameters, the dye/paper image experimental results documents that there is a positive correlation between cavitation effect and ultrasonic frequency/power. The enrichment degree of fixed adsorbate (0.1 μg L−1) under high frequency (59 kHz) or high-power input (100%) is 1–2 times higher than that under low frequency (40 kHz) or low power (60%) input. This is a valuable conclusion for the subsequent study of US dispersion of magnetic and even non-magnetic powder materials. In addition, the in-situ desorption and accurate measurement of adsorbed mercury were realized by combining slurry vapor generation atomic fluorescence spectroscopy (SVG-AFS). The constructed US assisted magnetic solid phase extraction (US-MSPE) method has the characteristics of low detection limit (0.36 ng L−1), high recovery (>90%), sustainable utilization (>3) and reasonable measurement deviation (<5%), which can meet the requirements of ultra-trace Hg2+ (0.01–1.0 μg L−1).

Preparation and characterization of ultra-small, monodisperse CoxFe3-xO4 nanoparticles

The application of magnetite nanoparticles to functional magnetic materials requires the ability to tune their magnetic properties. Doping of transition metals offers the ability to control the magnetic and electron transport properties of magnetite nanoparticles. Herein, we describe a synthetic approach to producing ultra-small (∼6 nm), monodisperse Co-doped magnetite (CoxFe3-xO4) nanoparticles, capped with oleic acid, using a modified co-precipitation method under mild conditions. For stoichiometric amounts of Co corresponding to x = 0.1, 0.3, and 0.5, we measured compositions of Co0.12Fe2.88O4, Co0.33Fe2.67O4, and Co0.58Fe2.42O4, respectively, using XPS analysis. Although a minor impurity of α-FeOOH was detected, this impurity was found to reduce significantly with increasing Co content. The resulting CoxFe3-xO4 nanoparticles showed significant increase in both the coercive field, and the blocking temperatures with increasing Co content, due to increased magnetic anisotropy. Magnetic characterization further revealed saturation magnetization values higher than those reported for CoxFe3-xO4 nanoparticles of similar size, monodispersity and Co content, prepared by other methods.

Effects of Sintering Temperature on Microstructural Properties of Ni1-xZnxFe2O4 Synthesized by Powder Metallurgy

Powder metallurgy (PM) is a modern manufacturing method that allows high-tech materials, alloys and complex shaped parts to be manufactured with precision and almost without the need for finishing operations such as deburring. PM basically involves powder production, powder processing, forming operations, pressing and sintering or pressure assisted hot consolidation. This paper reports results on Ni1-xZnxFe2O4 produced by powder metallurgy at different sintering temperatures. Ni1-xZnxFe2O4 is an interesting functional magnetic material due to its special properties such as stability, very good dielectric properties, electrical resistivity, low dielectric loss, chemical stability etc. all being important in cutting-edge technology. The use of Ni1-xZnxFe2O4 in diverse fields such as the biomedical field i.e. drug delivery is another vibrant research area. SEM imaging was performed for the structural analysis of the produced bulk sample. EDXRF analyses were performed for elemental composition along with SEM images.

A cyanide-bridged FeII–MoV-based coordination polymer showing spin crossover

A new cyanide–bridged Fe II –Mo V -based coordination polymer was synthesized. Magnetic and spectroscopic studies indicate that the 2D network displays an incomplete spin crossover (SCO). • A new cyanide-bridged Fe II –Mo V -based coordination polymer was synthesized. It is the first 2D [MoV(CN)]3–-based SCO complex. • X-ray diffraction, magnetic and IR spectra study revealed that 1 exhibited an incomplete spin transition with ca. 62% of the HS Fe II species transformed into the LS Fe II state. • magneto-structural analyses demonstrated that introducing more electron-donative ligands will improve the ligand field strength and therefore the completeness of SCO. Polycyanometallates are widely used in the construction of functional molecular magnetic materials owing to their versatile bonding modes and redox activities. However, only a few octacyanometallate-based complexes showed spin crossover (SCO) properties. In this work, we incorporate the bridging ligand 4,4'-Bis-(1H-imidazol-1-yl-methyl)biphenyl (bimb) into a cyanide-bridged Fe II –Mo V assembly, affording a two-dimensional spin crossover complex of {[Mo V (CN) 8 ][Fe II (bimb) 2 ]·0.5Hbimb} n ∙2H 2 O (1). The complex crystallizes in the P 1 ¯ space group and forms a layered structure. The two-dimensional layer is composed of one-dimensional [Fe II –CN–Mo V ] zigzag chains connected by the bridging ligand of bimb. Magnetic susceptibility measurements revealed that 1 exhibited an incomplete spin transition with ca. 62% of the high-spin (HS) Fe II species transitioned to the low-spin (LS) Fe II state upon cooling from 300 to 100 K.

Dynamic magnetomechanical behavior of sintered Nd2Fe14B under impact

As an important magnetic functional material, sintered NdFeB has gradually applied from mild places to environments that need to withstand impact. The reliability of materials to work in this environment has received extensive attention, but current research cannot provide corresponding support of experimental data and theoretical model for this problem yet. To tackle this, we carried out research on the magnetomechanical behavior of sintered NdFeB under dynamic impact environment. Specifically, dynamic mechanics and impact demagnetization experiments were conducted separately. Then, according to the characteristics of brittleness and strain rate dependence shown in dynamic mechanical experiments, a dynamic damage constitutive model was established. Additionally, a new magnetic degradation model was proposed in which the stress knee position existed and the relationship between impact load and irreversibility was established. The co-simulation model of impact demagnetization based on dynamic mechanical constitutive model and magnetic degradation model was designed to better display the demagnetization process of materials. Meanwhile, the parameter identification process was carried out to determine the unknown parameters in the model. Finally, the effectiveness of identified parameters were verified by comparing the simulation values with the experimental values.

Parametric Study to Evaluate the Geometry and Coupling Effect on the Efficiency of a Novel FMM Tool Embedded in Cover Concrete for Corrosion Monitoring

Rebar corrosion represents a major threat to the durability of reinforced concrete structures, primarily in marine environments. Various Non-Destructive Evaluations (NDE) have been developed to detect rebar corrosion; although most of these have delivered successful results, a lack of reliable techniques for proper corrosion prognosis still remains. Under the French Research Agency (ANR) project’s “LabCom OHMIGOD” framework, we introduce here a novel embedded tool to evaluate the level of cover concrete contamination from aggressive agents responsible for causing corrosion. This tool is divided into two parts: a reactive part exposed to corrosion, and a permanent part protected against corrosion. Using magnetic materials in both parts entails “Functional Magnetic Materials” (FMM) and generates a Magnetic Observable (MO). Through the evolution of corrosion on the reactive part, its magnetic properties become affected, which in turn modifies the MO. By means of regular monitoring of MO variations, it is possible to evaluate the aggressive agent ingress. Consequently, by using a variety of FMM tools placed at different concrete depths, it is possible to indirectly evaluate the rebar corrosion risk. This paper presents a numerical model of the tool employing Ansys software. The underlying objective is to investigate tool accuracy through its key parameters, namely, geometry, relative distance to the receiver, coupling effect, and border effect from the rebar. Simulation results demonstrate that by choosing an efficient geometry for the reactive part (25 mm × 25 mm × 1 mm) and position for the tool (between 1 and 3 mm), both a sufficient MO variation range and a negligible coupling effect can be obtained when the FMM is more than 5 cm from any ferromagnetic material.

Interaction of magnetic spheres in magnetic fields from the view of magnetic energy density: A 3D finite element analysis (FEA)

Magnetic interaction between magnetic particles is of great significance in the fields of magnetic separation and functional materials. A good understanding of interaction mechanism of magnetic particles would further boost its promising industrial applications. We hereby present our work which visualizes the movement behavior of magnetic spheres in magnetic fields employing high-speed imaging and simulates the dynamic behavior of spheres using an Arbitrary Lagrangian-Eulerian (ALE) based on finite element method. In this paper, we investigated the stress tensor, magnetic force, and dynamic behavior of magnetic spheres in magnetic fields, especially magnetic energy density in different domains. Results show that there are four relatively independent regions of magnetic energy density distribution in external spatial domains of a single sphere system. Attractive force will generate when the energy density in the spatial region between two spheres is relatively high, while a repulsive force will generate when the energy density in the spatial region between two spheres is relatively low. Every magnetic sphere spontaneously moves towards the region with high energy density and stays away from the region with low energy density. The total magnetic energy in magnetic spheres’ domains (V1) and external spatial domains (V2) increases, but the magnetic energy in the external spatial domain decreases over time during the aggregation process. The magnetic spheres ultimately arrange in chain-like structures oriented along magnetic field direction. We hereby proposed a novel and efficient approach to predict the movement trends and final state of magnetic particle swarm from the view of energy density.

Beyond Conventional Ferromagnetism and Antiferromagnetism: A Phase with Nonrelativistic Spin and Crystal Rotation Symmetry

The search for novel magnetic quantum phases, phenomena and functional materials has been guided by relativistic magnetic-symmetry groups in coupled spin and real space from the dawn of the field in 1950s to the modern era of topological matter. However, the magnetic groups cannot disentangle non-relativistic phases and effects, such as the recently reported unconventional spin physics in collinear antiferromagnets from the typically weak relativistic spin-orbit coupling phenomena. Here we discover that more general spin symmetries in decoupled spin and crystal space categorize non-relativistic collinear magnetism in three phases: conventional ferromagnets and antiferromagnets, and a third distinct phase combining zero net magnetization with an alternating spin-momentum locking in energy bands, which we dub "altermagnetic". For this third basic magnetic phase, which is omitted by the relativistic magnetic groups, we develop a spin-group theory describing six characteristic types of the altermagnetic spin-momentum locking. We demonstrate an extraordinary spin-splitting mechanism in altermagnetic bands originating from a local electric crystal field, which contrasts with the conventional magnetic or relativistic splitting by global magnetization or inversion asymmetry. Based on first-principles calculations, we identify altermagnetic candidates ranging from insulators and metals to a parent crystal of cuprate superconductor. Our results underpin emerging research of quantum phases and spintronics in high-temperature magnets with light elements, vanishing net magnetization, and strong spin-coherence.

A novel metallurgical technique for the preparation of soft magnetic iron carbide from low-grade siderite

Iron carbide (Fe3C) has attracted widespread attention as a functional material, catalyst, and magnetic material. In this study, soft magnetic Fe3C was prepared by carburization roasting, magnetic separation, and acid leaching using low-grade siderite as the raw material. The effects of carburization, subsequent magnetic separation, and acid leaching of the carburized samples on their magnetic properties were studied using a vibrating sample magnetometer (VSM), and the mechanisms of these methods were also studied. The final samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), VSM, and Mössbauer spectroscopy. Under optimized conditions, an iron carbide material comprising assaying 92.08% Fe and 6.94% C with a corresponding iron recovery rate of 73.50% was obtained. The saturation magnetization, the remanence, and coercivity values of the obtained iron carbide were 136.10 emu/g, 1.84 emu/g, and 39.11 Oe, respectively. Furthermore, Na2SO4 and NaOH were found to be useful additives for improving the carburization efficiency of iron carbide, enlarging iron carbide particles, improving the embedding relationship between iron carbide and gangue, and enhancing the dissolution of gangue in acid. The proposed technique is promising for the preparation of magnetic iron carbide materials with good soft magnetic performance.

Polydopamine-mediated modification of ZIF-8 onto magnetic nanoparticles for enhanced tetracycline adsorption from wastewater

Magnetic nanoparticle materials which could be used to remove tetracycline were confined seriously due to their poor stability and unsatisfactory reusability. Here, we facilely prepared novel zeolitic imidazolate framework-8 (ZIF-8) functionalized magnetic nanoparticles (Fe3O4@PDA-ZIF-8) adsorbent utilizing polydopamine as a bond to establish a connection between zeolitic imidazolate framework-8 and Fe3O4, which could improve the stability of magnetic nanoparticles and enhance the tetracycline adsorption capacity simultaneously. The prepared nanocomposites were characterized and their TC adsorption abilities under various experiment conditions (contact time, TC initial concentration and pH values) were also investigated. Experimental results proved that the prepared adsorbent showed superior TC adsorption capacities (92.01 mg/g at pH = 7). Further, the adsorption mechanisms were comprehensively studied and the prepared adsorbent showed satisfactory stability and reusability during the cycle experiment. Altogether, our findings provided a feasible way to design and construct functional magnetic MOF materials for enhancing tetracycline adsorption from wastewater.

Numerical and experimental study to investigate the performance of a novel embedded SHM tool to evaluate chloride front probability of reinforced concrete structures

Rebar's corrosion is a serious problematic of civil constructions that hugely reduces the serviceability of structure, mainly in maritime zone due to aggressive agents that could lead to corrosion. For decades, many Non-Destructive (ND) methods have been developed to address this issue, however, most of them focus on diagnosis the rebar’s corrosion and there is a lack of reliable techniques for prognosis. Under framework of French ANR project LabCom OHMIGOD, we want to propose a novel Structural Health Monitoring (SHM) embedded tool for detection of chlorides penetration front in cover concrete, as preventive ND method. It calls Functional Magnetic Material (FMM) by using magnetic and ferromagnetic materials. The output signature is magnetic flux density (B), as Magnetic Observable (MO). Embedding FMM tool in concrete, exposes to chlorides penetration, it would be corroded. By evolution of corrosion, its geometrical and physical properties would be changed and it causes the MO variations. Using an external interrogator and regular monitoring, we aim to evaluate the probability of chloride ions in media, associated with MO variations caused by corrosion. To evaluate the tool’s performance, we would investigate the amount of MO variations by numerical modeling of corrosion on FMM tool and experimental test. Firstly, through parametric study on geometrical variation and also evolution of corrosion products layer on the tool, as index of corrosion, the amount of MO variations is investigated. Secondly, through a real time monitoring test of FMM tool, placed on concrete core and corroded by accelerating corrosion for 46 hours, the MO variations are also measured. Comparing the numerical modeling and experimental results demonstrate an upward MO tendency, in line with corrosion. Moreover, a similar relative MO variation range is obtained (about 14.01\% and 12.05\%, respectively, for experimental and numerical modeling) that validates the FMM tools performance as novel SHM technique.

Experimental Parametric Study of a Functional-Magnetic Material Designed for the Monitoring of Corrosion in Reinforced Concrete Structures

The presence of aggressive agents (such as chloride ions brought by seawater) in reinforced concrete structures is responsible for the corrosion of the steel rebars. A Structural Health Monitoring technology is developed as a new passive preventive method that would allow for the detection of and for the ability to follow the presence of chloride ions in the cover concrete of reinforced concrete. This technology, referenced as Functional Magnetic Material (FMM), consists on the measurement with an external interrogator of a Magnetic Observable (MO), partially shielded by a patch and corrodible by chloride ions. This paper presents the results of a parametric experimental study, allowing the validation of the concept of this technology, by highlighting the variation of the MO while considering the geometry and the corrosion level of the patch (based on its Relative Mass Loss—RML), as well as the distance between the samples and the interrogator. The results show that the MO of the FMM significantly varies with the increase in the RML of the patch. A 10%-RML for the patch is sufficient for detecting a variation of the MO of the FMM, and the relative variations of the MO are strongly dependent on the distance between the FMM and the magnetometer, as well as the patch’s thickness.

A comparative study on adsorption and catalytic degradation of tetracycline by five magnetic mineral functional materials prepared from steel pickling waste liquor

Palygorskite (Pal), bentonite (Bent), sepiolite (Sep), zeolite (Zeol), and kaolin (Kaol) were used with steel pickling waste liquor to synthesize magnetic palygorskite (Pal@Fe3O4), magnetic bentonite (Bent@Fe3O4), magnetic sepiolite (Sep@Fe3O4), magnetic zeolite (Zeol@Fe3O4), and magnetic kaolin (Kaol@Fe3O4), for adsorption and catalytic degradation of tetracycline (TC), respectively. Through the study of adsorption kinetics and adsorption isotherms, the maximum adsorption capacity of Pal@Fe3O4 to TC was 149.439mg/g, which was 1.239 times, 2.260 times, 3.161 times, and 3.448 times of Bent@Fe3O4, Zeol@Fe3O4, Kaol@Fe3O4, and Sep@Fe3O4, respectively. The kinetic study of tetracycline degradation demonstrated that the maximum reaction rate constant of Bent@Fe3O4/H2O2 system was K(obs) = 2.12 × 10-2min-1, which was close to that of Pal@Fe3O4/H2O2, Kaol@Fe3O4/H2O2 system, and was 2.000 times, 2.356 times, 2.650 times, and 4.711 times of Fe3O4/H2O2, Zeol@Fe3O4/H2O2, Sep@Fe3O4/H2O2, and H2O2 system, respectively. The results showed that Pal@Fe3O4 and Bent@Fe3O4 were more advantageous in the treatment of wastewater containing tetracycline, and efficient reuse of exhausted magnetic minerals and deep mineralization of organic pollutants were achieved by constructing an advanced oxidation system. The BET, VSM, SEM, XPS, XRD, and FTIR were used to characterize the five clay minerals before and after magnetic modification. It was speculated that the surface structure - OH groups of clay minerals might be significant factors influencing the adsorption performance of magnetic minerals on TC, and reduction ability of clay minerals to Fe3+ importantly affected the catalytic performance of magnetic minerals. The specific surface area and morphological structure of clay minerals both affected the adsorption and catalytic degradation of TC by the five magnetic minerals.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures.

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (LnIII). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Effects of Fe, Mn Individual Doping and (Fe, Mn) Co-Doping on Ferromagnetic Properties of Co2Si Powders.

Magnetic materials are crucial energy materials that are widely used in day-to-day life. Therefore, the development and study of high-performance magnetic materials are of great significance. In this study, the magnetic materials CoSi, CoXSi (X = Fe, Mn), and CoFeMnSi were prepared via the ball milling and sintering processes. Their crystal structures, electrical conductivity, and magnetic properties were investigated via the X-ray diffraction analysis and by using a resistivity tester, vibrating sample magnetometer, and vector network analyser. The X-ray diffraction analysis revealed that a single phase of CoSi and its doped alloy powders were successfully obtained. The electrical conductivities of MnCoSi and FeMnCoSi were measured using a resistivity tester. The results indicate that Mn doping and Fe and Mn Co-doping enhanced the electrical conductivity of CoSi. The magnetic properties of CoSi were determined using a vibrating sample magnetometer. We observed that the magnetic properties were enhanced after doping. CoFeMnSi exhibited excellent magnetic properties. Further, its permeability was determined using a vector network analyser. At a low frequency, the u’ and u” values of CoFeSi and CoFeMnSi were enhanced; whereas, at a high frequency, after doping, the u’ and u” values changed only slightly. This study can be used as a basis for future studies on magnetic functional materials.

Experimental study on adsorption properties of functional magnetic nano materials for heavy metal pollutants

Experimental study on adsorption properties of functional magnetic nano materials for heavy metal pollutants

Design and Anticorrosion Prediction of Functional Dilute Magnetic Solid Solution Materials

Design and Anticorrosion Prediction of Functional Dilute Magnetic Solid Solution Materials

Investigation into the magnetic properties of CoFeNiCr y Cu x alloys

The search for cheap, corrosion-resistant, thermally-mechanically stable functional magnetic materials, including soft magnetic and magneto-caloric materials has led to research focused on high entropy alloys (HEAs). Previous research shows that alloying elements with negative enthalpies of mixing can facilitate a second-order phase transition. On the other side of the spectrum, compositional segregation cause by positive enthalpy of mixing alloying additions (such as Cu) may also be used to tune magnetic properties. This paper studies the structural, magnetic and magneto-caloric effect of the FCC alloys CoFeNiCr y Cu x (x = 0.0, 0.5, 1.0 and 1.5, y = 0.0, 0.8 and 1.0) to tune these properties with Cu and Cr alloying. Scanning electron microscopy of the compositions show nanoparticles forming within the grains as the Cu concentration increases. Cr addition to CoFeNiCu1.0 has a larger effect on the magnetic and magneto-caloric properties compared to the Cu addition to CoFeNiCr1.0. The addition of Cu (x = 0.5) to CoFeNiCr1.0 improved both the saturation magnetisation and Curie temperature; addition of Cr (y = 1.0) to CoFeNiCu1.0 decreased the Curie temperature by 900 K. All alloys were determined to have a second-order phase transition around their Curie temperature. The refrigerant capacity at 2 T was found to be similar to existing HEAs, although the Curie temperatures were lower than room temperature. Based on this data the CoFeNiCr0.8Cu composition was fabricated to increase the Curie temperature towards 300 K to explore these HEAs as new candidates for room temperature magneto-caloric applications. The fabricated composition showed Curie temperature, saturation magnetisation, and refrigerant capacity increasing with the small reduction in Cr content.