Related Magnetic Properties Research Articles

A Comprehensive Study of Pristine and Calcined f-MWCNTs Functionalized by Nitrogen-Containing Functional Groups.

We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and 57Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe3C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe3C as evidenced by a Curie temperature estimated at TC = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.

Two-dimensional magnetic transition metal halides: molecular beam epitaxy growth and physical property modulation

The spontaneous magnetization of two-dimensional (2D) magnetic materials can be maintained down to the monolayer limit, providing an ideal platform for understanding and manipulating magnetic-related properties on a 2D scale, and making it important for potential applications in optoelectronics and spintronics. Transition metal halides (TMHs) are suitable 2D magnetic candidates due to partially filled d orbitals and weak interlayer van der Waals interactions. As a sophisticated thin film growth technique, molecular beam epitaxy (MBE) can precisely tune the growth of 2D magnetic materials reaching the monolayer limit. Moreover, combining with the advanced experimental techniques such as scanning tunneling microscopy, the physical properties of 2D magnetic materials can be characterized and manipulated on an atomic scale. Herein, we introduce the crystalline and magnetic structures of 2D magnetic TMHs, and show the 2D magnetic TMHs grown by MBE and their electronic and magnetic characterizations. Then, the MBE-based methods for tuning the physical property of 2D magnetic TMHs, including tuning interlayer stacking, defect engineering, and constructing heterostructures, are discussed. Finally, the future development opportunities and challenges in the field of the research of 2D magnetic TMHs are summarized and prospected.

PM2.5 Magnetic Properties in Relation to Urban Combustion Sources in Southern West Africa

The physico-chemical characteristics of particulate matter (PM) in African cities remain poorly known due to scarcity of observation networks. Magnetic parameters of PM are robust proxies for the emissions of Fe-bearing particles. This study reports the first magnetic investigation of PM2.5 (PM with aerodynamic size below 2.5 μm) in Africa performed on weekly PM2.5 filters collected in Abidjan (Ivory Coast) and Cotonou (Benin) between 2015 and 2017. The magnetic mineralogy is dominated by magnetite-like low coercivity minerals. Mass normalized SIRM are 1.65 × 10−2 A m2 kg−1 and 2.28 × 10−2 A m2 kg−1 for Abidjan and Cotonou respectively. Hard coercivity material (S-ratio = 0.96 and MDF = 33 mT) is observed during the dry dusty season. Wood burning emits less iron oxides by PM2.5 mass when compared to traffic sources. PM2.5 magnetic granulometry has a narrow range regardless of the site or season. The excellent correlation between the site-averaged element carbon concentrations and SIRM suggests that PM2.5 magnetic parameters are linked to primary particulate emission from combustion sources.

Structural and Functional Diversity in Lead-Free Halide Perovskite Materials.

Lead halide perovskites have emerged as promising semiconducting materials for different applications owing to their superior optoelectronic properties. Although the community holds different views toward the toxic lead in these high-performance perovskites, it is certainly preferred to replace lead with nontoxic, or at least less-toxic, elements while maintaining the superior properties. Here, the design rules for lead-free perovskite materials with structural dimensions from 3D to 0D are presented. Recent progress in lead-free halide perovskites is reviewed, and the relationships between the structures and fundamental properties are summarized, including optical, electric, and magnetic-related properties. 3D perovskites, especially A2 B+ B3+ X6 -type double perovskites, demonstrate very promising optoelectronic prospects, while low-dimensional perovskites show rich structural diversity, resulting in abundant properties for optical, electric, magnetic, and multifunctional applications. Furthermore, based on these structure-property relationships, strategies for multifunctional perovskite design are proposed. The challenges and future directions of lead-free perovskite applications are also highlighted, with emphasis on materials development and device fabrication. The research on lead-free halide perovskites at Linköping University has benefited from inspirational discussions with Prof. Olle Inganäs.

Non-isothermal crystallization kinetics and soft magnetic properties of the Fe67Nb5B28 metallic glasses

Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe67Nb5B28 metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol−1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol−1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe2B, and Fe23B6 phases, and further annealing leads to the formation of α-Fe, Fe2B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe67Nb5B28 metallic glasses are discussed.

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface**Project supported by the National Natural Science Foundation of China (Grant Nos. 61390501, 51325204, and 11204361), the National Basic Research Program of China (Grant Nos. 2011CB808401 and 2011CB921702), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2013YQ1203451), the National Supercomputing Center in Tianjin, China,

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine (H2Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory (DFT) based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

On the Anomalous Magnetic Behavior and the Multiferroic Properties in BiMn2O5

Sealed-tube synthesis of BiMn2O5 materials and their physical properties have rationally been reinvestigated depending on the reactants. The aim of the study was to characterize its potential multiferroic properties and to investigate the anomalous magnetic properties in relation to the expected ferroelectric properties. Rietveld refinement of the room temperature X-ray diffraction data shows the stability of the crystallographic structure with a Mn(3+)/Mn(4+) ratio far from 1 because of bismuth and oxygen deficiencies despite the sealed-tube synthesis. Our detailed magnetic susceptibility and specific heat data analysis unambiguously support an intrinsic anomalous magnetic behavior in relation to the establishment of a magnetic short-range ordering far from the Néel temperature. Around room temperature, oxygen vacancies are responsible for supporting the dielectric loss peak measured, and, interestingly, the so-called T*, which was underlined in relation to an anomalous phonon shift (García-Flores, A. F.; et al. Phys. Rev. B 2006, 73, 104411), is not a characteristic temperature in relation to the multiferroic properties because no ferroelectric transition was detected.

Prismatic magnetite magnetosomes from cultivated Magnetovibrio blakemorei strain MV‐1: a magnetic fingerprint in marine sediments?

The magnetic properties (first-order reversal curves, ferromagnetic resonance and decomposition of saturation remanent magnetization acquisition) of Magnetovibrio blakemorei, a cultivated marine magnetotactic bacterium, differ from those of other magnetotactic species from sediments deposited in lakes and marine habitats previously studied. This finding suggests that magnetite produced by some magnetotactic bacteria retains magnetic properties in relation to the crystallographic structure of the magnetic phase produced and thus might represent a 'magnetic fingerprint' for a specific magnetotactic bacterium. The use of this fingerprint is a non-destructive, new technology that might allow for the identification and presence of specific species or types of magnetotactic bacteria in certain environments such as sediments.

Electronic structure of grain boundaries in the Fe86-Mn12.7-C1.3alloy

The importance of studying Fe-Mn-C alloys is related to their wide use as constructional materials in mechanical engineering. In this work an effort has been made to elucidate the physical origin of the magnetization in austenitic steels by calculating the electronic structure of grain boundaries. To theoretically investigate the magnetic properties of a crystal of ferromagnetic bcc iron, the wave functions of the iron atom calculated in view of the spin polarization of a core by the Hartree-Fock method with local exchange-correlation potentials have been used as base functions. This has made it possible to optimize the choice of a zero approximation for the description of the electronic states of ferromagnetic iron and to attain good agreement with the experimental values of the magnetic moment (μ theor = 2.23μ B , μ exp = 2.218μ B ), of the exchange splitting of the crystal term P 4 (Δ theor = Δ exp = 0.112 Ry), and of the cross-sections of the Fermi surface. A similar approach has been used to investigate the magnetic states of clusters (nanoclusters) based on the method of scattered waves. The approach developed for clusters of the alloy under investigation makes it possible to calculate the alloy magnetic properties in relation to the cluster size for a varied lattice parameter.

Influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite

In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe 2.85RE 0.15O 4 (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe 2.85Gd 0.15O 4 and Fe 2.85Tm 0.15O 4, represent an extension of the previously published results on Fe 3O 4/γ-Fe 2O 3, Fe 2.85Y 0.15O 4 and Fe 2.55In 0.45O 4 [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic, Ph. Colomban, Sol. State Sciences 8 (2006) 908], while magnetic characterization has been done for all the samples.Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic (SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe 3O 4 had the largest H C and the lowest M S. We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility ( H > 20 kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy.

Magnetism-Related Properties of CdSb Revealed by the Zeeman 121Sb NQR Spectra

The 121Sb NQR spectra of CdSb single crystal were measured in the presence of weak (up to 500 Oe) external magnetic fields. As the analysis of the 121Sb EFG symmetry showed, two magnetically nonequivalent Sb sites exist in the CdSb crystal lattice. An upper limit of the local magnetic field, which may exist in CdSb characterized with the observed 121Sb NQR spectra, was estimated by modeling the Zeeman perturbed patterns. This amounted to H loc ∼10 G, hence being much less than earlier found local fields H loc ≈30–200 G in bismuth-based compounds.

Preparation of highly conductive Mn-doped Fe3O4 thin films with spin polarization at room temperature using a pulsed-laser deposition technique

We report on the preparation of MnxFe3−xO4 (x=0, 0.1, or 0.5) epitaxial thin films using a pulsed-laser deposition technique. Conditions for modified film formation are discussed, in addition to their electrical and magnetic properties in relation to the potential development of room temperature spin electronics devices. The film with x=0.1 could be fabricated at a higher substrate temperature (600°C) than the Fe3O4 thin film without Mn doping. The doped films exhibited low resistivity of about 7.0×10−3(x=0.1)–9.0×10−2(x=0.5)Ωcm at room temperature. Moreover, a spin polarization of the carrier of MnxFe3−xO4 (x=0, 0.1, or 0.5) films was confirmed at room temperature by examination of anomalous Hall coefficient measurements.

The origin of room temperature ferromagnetism in cobalt-doped zinc oxide thin films fabricated by PLD

We have fabricated Zn 0.75Co 0.25O thin films on sapphire (0001) substrates at different substrate temperatures (400–700 °C) in a fixed O 2 pressure of 1×10 −5 Torr using pulsed laser deposition technique and investigated their structural and magnetic properties in relation to the growth conditions. X-ray diffraction and transmission electron microscopy observations have revealed that hexagonal Co clusters are present in the films grown at 700 °C. At relatively low temperatures (400–600 °C), homogeneous alloy films of wurtzite structure are formed with an epitaxial relationship of (0001) ZnCoO∣∣(0001) sap and [01 1 ̄ 0] ZnCoO∣∣ 1 ̄ 2 1 ̄ 0] sap, which is the same as that for ZnO grown on (0001) sapphire. Observed results of the structural and magnetic properties collectively imply that the presence of the ferromagnetic Co clusters leads to ferromagnetism in Co-doped ZnO films.

Microelectrodeposition of Co–Pt alloys for micromagnetic applications

Miniaturisation of advanced devices, such as sensors and micromotors, requires the development of micromagnets of small size but with a high magnetostatic energy. Cobalt alloys, and in particular cobalt–platinum alloys, are proposed for such applications, as well as for magnetic recording, due to their magnetic and corrosion resistance properties. Such alloys can be electrodeposited with good magnetic properties at high thickness by addition of phosphorus and other elements that favour a stable growth of the microstructure during deposition. Results on electrodeposition of Co–Pt–W(P) and Co–Pt–Zn(P) layers from sulphamate citrate solutions are presented. Thick deposits of high coercivity and layers with different preferred orientation are obtained by changing the operation conditions. The deposits have magnetic anisotropy, which favours their implementation in magnetic circuits where the field is perpendicular or parallel to the surface: in the former case, the magnetic easy direction of cobalt alloys must be perpendicular to the surface and in the latter, it must be parallel to the surface. The magnetic properties of Co–Pt-based alloys can be tailored to obtain the desired magnetic properties in relation to the application envisaged.

Soft magnetism in nitrided Fe 93Ni 4Cr 3 and Fe 94Ni 4Ti 2 cold-rolled alloys

The magnetic properties in relation with the structure of nitrided cold-rolled Fe 93Ni 4Cr 3 and Fe 94Ni 4Ti 2 were studied. Various low-temperature nitriding treatments were applied in order to obtain soft magnetic materials. We show that the magnetic anisotropy depends sensitively on the nitrogen content. The lowest value of the coercive force, H C=40 A/m was obtained for samples containing TiN precipitates. For the Cr contained samples, a concentration of 14% (Fe–Ni) 4N (γ′)-phase decreases H C below values corresponding to the samples containing only CrN precipitates. We discuss the influence of the texture on the magnetic properties of samples containing only BCC α′-phase, a mixture of α′+γ′-phase, or samples which have been cycled through the ε-phase. Although grain refinement is observed after cycling and an almost random orientation of the grains is obtained, the magnetic properties do not improve. This is due to the fact the grain size is still too large to lead to averaging out of the magnetic anisotropy. Moreover, the stress/strain distribution developed during the treatments hampers domain wall motion and leads to an increased coercivity.

衝撃波圧力と物質ダイナミクス 衝撃圧縮を用いた非平衡バルク磁性体の創製

Shock compression can be used to consolidate a nonequilibrium alloy or compound powders without recrystallizing or decomposition, taking advantage of the high pressure and short duration, in addition it can be used to synthesize high-pressure phases. Mechanical alloying (MA) has also recently been used for nonequilibrium materials processing, including the preparation of metastable solid solution phases, amorphous phases, nano crystals, etc. We have been preparing nonequilibrium bulk materials consisting of such metastable phases in the transition metal systems or tungsten systems, etc. by using shock compression, and investigating the physical properties. Particularly, the metastable solid solution bulk alloys in transition metal systems showed interesting magnetic properties in relation to the Slater-Poring curve. In addition, a fully-dense Sm2Fe17Nx magnet was for the first time prepared. In this review, the topical magnetic properties of these metastable alloys (Fe-Co, Fe-Cu, Fe-W) and the Sm-Fe-N magnet are shown.

Spectroscopy and magnetism of polymeric Ln(CCl3COO)3·2 H2O and their heteronuclear Ln2Cu(CCl3COO)8·6 H2O analogues (Ln=Sm, Gd)

In order to study the exchange interactions between f- and d-electron ions two series of compounds, heteronuclear Ln2Cu(CCl3COO)8· 6 H2O (1, Sm; 2, Gd) and polymeric Ln(CCl3COO)3·2 H2O (3, Sm; 4, Gd) trichloroacetates, were synthesised. Polymeric trichloroacetates 3 and 4 are isomorphous with erbium chloroacetate, whose structure contains dimeric units linked by carboxyl bridges and water molecules into endless chains. Heteronuclear 1 and 2 are isomorphous with Nd2Cu(CCl3COO)8·6 H2O reported by us previously. Absorption spectra of single crystals of 1–4 for two orientations of the crystals down to 4 K were investigated. Magnetic susceptibility measurements in the range 300–1.8 K were carried out. Optical and magnetic properties are related to the X-ray data. Electron transition probabilities were calculated and the effect of coupled ion pairs in the polymeric structure on the optical and magnetic properties was analysed. Changes in magnetic properties in relation to the mononuclear systems are discussed.

Annealing effect of surface magnetic properties in amorphous Co/sub 1-x/Ti/sub x/ thin films

For amorphous Co/sub 1-x/Ti/sub x/ (x=0.13, 0.16, 0.21 at.%) thin films, deposited by the DC magnetron sputtering method, ferromagnetic resonance experiments have been used to investigate the dependence of surface magnetic properties in relation to annealing temperatures (150/spl sim/225/spl deg/C). Spin wave resonance spectra for all annealing temperatures consist of several volume modes and one (or two) surface mode. It is suggested that both surfaces of the film have a perpendicular hard axis to the film plane (negative surface anisotropy). Also, the surface anisotropy K/sub s2/ at the substrate-film interface is varied slowly from -0.11 to -0.25 erg/cm/sup 2/ and the surface anisotropy K/sub s1/ at the film-air interface is varied from 0.16 to -0.53 erg/cm/sup 2/ with increasing annealing temperatures. We conjecture that the variation of surface anisotropy K/sub s1/ is due to the increase of Co concentration resulting from Ti oxidation for low temperature annealing (150-200/spl deg/C) and the diffusion of Co atoms near the film surfaces for high temperature annealing (225-250/spl deg/C).

Magnetic Properties in Relation to Chemical Constitution

IN the recent letter by Prof. Lowry and Mr. Gilbert (NATURE, Jan. 19, p. 85) some interesting points are dealt with concerning the evidence afforded by magnetic data as to the chemical constitution of various compounds. The authors note that the fact that cupric sulphide, CuS, is diamagnetic suggests that this compound must be a cuprous compound with a double molecule rather than a cupric salt as previously supposed. They also mention that X-ray analysis has shown that iron pyrites must be a ferrous disulphide, Fe++&Smacr;-&Smacr;.

Magnetic Properties in Relation to Chemical Constitution

THROUGH the kindness of Dr. Kapitza and Dr. Webster, we have had the opportunity of examining in the Cambridge Magnetic Laboratory a number of compounds to which formulae with single-electron bonds have been assigned. These compounds are of two principal types: (1) Pervalent salts, including PCl5, SbCl5, SbMe3Cl2, SbMe3Br2, SbMe3I2, the α and β forms of TeMe2Cl2, TeMe2Br2 and TeEt2I2, μ-TeMe2I2 and μ-TeMe2I4, and a number of analogous compounds such as PCl3, POCl3, AlCl3, TlI3, BiI3, CsI3. (2) Co-ordination compounds, including the Li·, Be··, Al···, Co··, Ni··, and Fe··· derivatives of benzoylcamphor. Except in the case of substances containing a metal of the transition series, these compounds have all proved to be diamagnetic. We therefore conclude that all the electrons are magnetically paired, just as they are in compounds in which the valency-electrons are present as pairs of shared electrons or as ‘lone pairs’ of unshared electrons. The numerical results of these experiments will be published later.