Mechanism Of Magnetic Interactions Research Articles

Hypomagnetic Conditions and Their Biological Action (Review).

The geomagnetic field plays an important role in the existence of life on Earth. The study of the biological effects of (hypomagnetic conditions) HMC is an important task in magnetobiology. The fundamental importance is expanding and clarifying knowledge about the mechanisms of magnetic field interaction with living systems. The applied significance is improving the training of astronauts for long-term space expeditions. This review describes the effects of HMC on animals and plants, manifested at the cellular and organismal levels. General information is given about the probable mechanisms of HMC and geomagnetic field action on living systems. The main experimental approaches are described. We attempted to systematize quantitative data from various studies and identify general dependencies of the magnetobiology effects' value on HMC characteristics (induction, exposure duration) and the biological parameter under study. The most pronounced effects were found at the cellular level compared to the organismal level. Gene expression and protein activity appeared to be the most sensitive to HMC among the molecular cellular processes. The nervous system was found to be the most sensitive in the case of the organism level. The review may be of interest to biologists, physicians, physicists, and specialists in interdisciplinary fields.

Magnetic Materials via High-Pressure Torsion of Powders

Magnets are key materials for the electrification of mobility and also for the generation and transformation of electric energy. Research and development in recent decades lead to high performance magnets, which require a finely tuned microstructure to serve applications with ever increasing requirements. Besides optimizing already known materials and the search on novel material combinations, an increasing interest in unconventional processing techniques and the utilization of magnetic concepts is apparent. Severe plastic deformation (SPD), in particular by high-pressure torsion (HPT) is a versatile and suitable method to manufacture microstructures not attained so far, but entitling different magnetic coupling mechanisms fostering magnetic properties. In this work, we review recent achievements obtained by HPT on soft and hard magnetic materials, focusing on powder as starting materials. Furthermore, we give specific attention to the formation of magnetic composites and highlight the opportunities of powder starting materials for HPT to exploit magnetic interaction mechanisms.

Effects of extremely low frequency electromagnetic fields on the tumor cell inhibition and the possible mechanism

Low-frequency magnetic fields exert a significant inhibitory effect on tumor growth and have been developed as a therapeutic modality. However, the effect of a low-frequency magnetic field on the interaction between cells is still poorly understood. This study aimed to preliminarily evaluate the direct effect of magnetic field ditectely on cultured cells and indirect effect mediated by cell-environment (conditioned medium). 293 T cells, Hepg2 cells, A549 cells have been cultured at 37 ± 0.18 °C in presence of an extremely low-frequency magnetic field of 20 Hz, 5-mT. The adherent tumor cells were more sensitive to magnetic field inhibition in the original environment (conditioned medium) with adherence inhibition rate for Hepg2 and A549 estimated at 18% and 30% respectively. The inhibition effect was suppressed when the suspended cells separated or clump density at a low density. The nontumor cell lines showed no inhibitory effect on exposure to a low-frequency magnetic field. The intracellular ion fluorescence (IIF) showed that the magnetic field significantly altered the membrane potential, indicating hyperpolarization of the adherent cells (ΔIIF 293 T cells: − 25%, ΔIIF Hepg2 cells: − 20% and ΔIIF A549 cells: − 13%) and depolarization of the suspended cells (ΔIIF Raji cells: + 9%). In addition, the conditioned media collected after magnetic field exposure acted on unexposed tumor cells and caused inhibition. Our findings might provide a basis for the mechanism of magnetic field interaction between cells and cell environment in the future.

Collective Quantum Magnetism in Nitrogen-Doped Nanographenes.

The emergence of quantum magnetism in nanographenes provides ample opportunities to fabricate purely organic devices for spintronics and quantum information. Although heteroatom doping is a viable way to engineer the electronic properties of nanographenes, the synthesis of doped nanographenes with collective quantum magnetism remains elusive. Here, a set of nitrogen-doped nanographenes (N-NGs) with atomic precision are fabricated on Au(111) through a combination of imidazole [2+2+2]-cyclotrimerization and cyclodehydrogenation reactions. High-resolution scanning probe microscopy measurements reveal the presence of collective quantum magnetism for nanographenes with three radicals, with spectroscopic features which cannot be captured by mean-field density functional theory calculations but can be well reproduced by Heisenberg spin model calculations. In addition, the mechanism of magnetic exchange interaction of N-NGs has been revealed and compared with their counterparts with pure hydrocarbons. Our findings demonstrate the bottom-up synthesis of atomically precise N-NGs which can be utilized to fabricate low-dimensional extended graphene nanostructures for realizing ordered quantum phases.

Recent advances in two-dimensional van der Waals magnets

Two-dimensional (2D) magnets have evoked tremendous interest within the research community due to their fascinating features and novel mechanisms, as well as their potential applications in magnetic nanodevices. In this review, state-of-the-art research into the exploration of 2D magnets from the perspective of their magnetic interaction and order mechanisms is discussed. The properties of these magnets can be effectively modulated by varying the external parameters, such as the charge carrier doping, thickness effect, pressure and strain. The potential applications of heterostructures of these 2D magnets in terms of the interlayer coupling strength are reviewed, and the challenges and outlook for this field are proposed.

Nonequilibrium, weak-field-induced cyclotron motion: A mechanism for magnetobiology.

There is a long-time quest for understanding physical mechanisms of weak magnetic field interaction with biological matter. Two factors impeded the development of such mechanisms: first, a high (room) temperature of a cellular environment, where a weak, static magnetic field induces a (classically) zero equilibrium response. Second, the friction in the cellular environment is large, preventing a weak field to alter nonequilibrium processes such as a free diffusion of charges. Here we study a class of nonequilibrium steady states of a cellular ion in a confining potential, where the response to a (weak, homogeneous, static) magnetic field survives strong friction and thermal fluctuations. The magnetic field induces a rotational motion of the ion that proceeds with the cyclotron frequency. Such nonequilibrium states are generated by a white noise acting on the ion additionally to the nonlocal (memory-containing) friction and noise generated by an equilibrium thermal bath. The intensity of this white noise can be weak, i.e., much smaller than the thermal noise intensity.

Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd0.5Pr0.5FeO3 single crystal* *Project supported by the National Natural Science Foundation of China (Grant Nos. 12074242 and 51862032), the Ministry of Science and Higher Education of Russia (theme “Spin” No. AAAA-A-18-118020290104-2), and the Government of the Russian Federation (Grant No. 02.A03.21.0006)

The single crystals of Nd0.5Pr0.5FeO3 were successfully grown by optical floating zone method. Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal. The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure. At high temperatures (T > 66 K), it shows the typical characteristics of Γ 4(G x , A y , F z ) state. With the decrease of the temperature, it undergoes a first-order spin reorientation transition from Γ 4(G x , A y , F z ) to Γ 2(F x , C y , G z ) state in the temperature window of 45–66 K under an applied magnetic field of 0.01 T. As the temperature drops to ∼ 17 K, a new magnetic interaction mechanism works, which results in a further enhancement of magnetization. The T–H phase diagram of Nd0.5Pr0.5FeO3 single crystal was finally constructed.

Understanding defect-mediated cubic to hexagonal topotactic phase evolution in SrMnO3 thin films and associated magnetic and electronic properties

The coupling between the oxygen stoichiometry and strain-induced lattice distortions has huge bearings on the electronic and magnetic properties of $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ (SMO). In this paper we have observed oxygen stoichiometry-mediated epitaxial tetragonal to nonepitaxial-oriented hexagonal topotactic phase transition of $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ thin film on $\mathrm{SrTi}{\mathrm{O}}_{3}$ (100) substrate. The oxygen stoichiometric hexagonal SMO films are oriented in nature, while the oxygen-deficient epitaxially strained $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ films are tetragonal in nature. It is observed that oxygen vacancy is obligatory to hold on the epitaxial strain in $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin film, while oxygenated stoichiometric cubic $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films are observed to be strain free. The structural phase and stoichiometry are found to govern the nature and mechanism of magnetic interactions in these films. The emergence of unusual weak ferromagnetism in oxygen stoichiometric hexagonal SMO films established a root towards the local structural distortion as confirmed through the Raman spectroscopy and extended x-ray absorption fine structure measurements. This work proves for us the idea that the oxygen deficiency is not the necessary effect of strain; rather, it is the cause of strain for topotactic SMO film.

Magnetic two‐dimensional layered crystals meet with ferromagnetic semiconductors

AbstractThe existence of intrinsic ferromagnetic semiconductors (FMSs) in two‐dimensional (2D) materials has been a long‐term concern and pursuit. Recent breakthroughs in the 2D FMSs, such as CrGeTe3 and CrX3 (X = Cl, Br, I) from bulk down to monolayer, have stimulated intensive researches on new physical phenomena and creative concepts. This minireview mainly summarizes recent progress of 2D intrinsic FMSs in theoretical side, and focuses on the ongoing strategies proposed to enhance ferromagnetism, involving the mechanisms of magnetic exchange interaction and the significance of magnetic anisotropy. Meanwhile, spin‐related multifunctionality with ultrathin FMSs and their van de Waals heterostructures in magnetoelectric, valleytronic, and nondissipative electronic technology are introduced, as well as the current challenges and the prospects in this field are discussed.image

Optical properties of S2 and S3 excited states of protonated schiff-base retinal chromophores in TPA, ECD and ROA.

The electronic transitions of the protonated Schiff base of 1l-cis-retinal (PSB11) and protonated Schiff bases of all-trans retinal (PSBT) for the second or higher electronic excited states are hard to be observed experimentally, due to weak intensities of electronic state excitations. In this paper, we propose visualizations method to investigate these weak electronic state transitions of PSB11 and PSBT, using two-photon absorption (TPA), electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra. Because of the resonance excitations of PSB11 and PSB11 in TPA, the transition intensity of the third electronic state is significantly enhanced, which are much larger than that of S1 and S2 electronic transitions. The charge transfer and electron-hole coherence of these electronic transitions in each step in TPA are visualized with charge difference density and transition density matrix. Also, the strong absorptions of S1 and S2 electronic excited states are observed with ECD spectra, and the physical mechanism of electric and magnetic interactions for these electronic transitions are revealed by visualization method. The large intensity of ROA at S3 excited state results from transition electric and magnetic dipole interactions, not from transition electric dipole and transition electric quadrupole interactions. Our results provide a new visualization method to study the optical properties of biological system using TPA and ECD spectra.

Field-dependent anisotropic magnetic coupling in layered ferromagnetic Fe3−xGeTe2

Two-dimensional layered itinerant ferromagnetic ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ is considered as a candidate for applications in heterostructure-based spintronics because of its near-room-temperature Curie temperature and highly tunable characteristic of ferromagnetism. Moreover, the strong anisotropic magnetism of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ is another great advantage for fabricating magnetic storage devices. However, many relevant properties of its anisotropy still remain poorly understood, especially the basic mechanism of anisotropic magnetic interaction. In this work, we focus on the study of magnetic coupling in single-crystal ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ ($x\ensuremath{\approx}0.28$) by the anisotropic magnetization, magnetic entropy change, and critical behavior. Our results confirm that the magnetization is angle dependent $[M(\ensuremath{\varphi})]$, in which the easy magnetic axis is along the $c$ axis while it exhibits absolute isotropic property in the $ab$ plane. The magnetic entropy change $[\mathrm{\ensuremath{\Delta}}{S}_{M}]$ also reveals an anisotropic feature between $H//c$ and $H//ab$. By fitting the field-dependent parameters of $\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$, it gives the critical exponents $\ensuremath{\beta}=0.361(3), \ensuremath{\gamma}=1.736(7)$, and $\ensuremath{\delta}=5.806(8)$ for $H//c$, while $\ensuremath{\beta}=0.714(3), \ensuremath{\gamma}=1.243(7)$, and $\ensuremath{\delta}=2.741(1)$ for $H//ab$. The critical exponents with $H//c$ belong to the theoretical prediction of three-dimensional Heisenberg model, which suggest a short-range magnetic coupling. However, the critical exponents with $H//ab$ are close to those of mean-field model, which indicates a long-range magnetic coupling. The determined critical exponents suggest that the anisotropic magnetic coupling of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ is strongly dependent on orientations of the applied magnetic field.

Electron Spin Resonance Properties of CrI3 and CrCl3 Single Crystals

ABSTRACTDeveloping functional, cleavable two-dimensional materials for use in next generation devices has recently become a topic of considerable interest due to their unique properties. Of particular interest, transition metal halides CrI3 and CrCl3 have shown to be good contenders for tunable and cleavable magnetic materials due to their unique magnetic properties in the monolayer. Here, electron spin resonance spectroscopy is used to pinpoint the atomic origins and underlying mechanisms of magnetic interactions as a function of temperature (5-500 K) and microwave frequency (9.43, 120 GHz) on CrI3 and CrCl3 bulk single crystals. ESR signals from CrI3 due to Cr3+ were observed to decay at 460 K, while ESR signals from CrCl3 remain up to 500 K. In the case of CrCl3, the temperature dependences of signal behavior, line width and g-value show characteristic signatures of ferromagnetic fluctuations at around 40 K, near to the antiferromagnetic phase transition at 17 K.

Unusual interfacial magnetic interactions for τ-MnAl with Fe(Co) atomic layers.

The interfacial magnetic interaction and coupling mechanism for τ-MnAl with Fe(Co) atomic layers have been studied using first principles calculations. The stable surface and interface were firstly determined by the surface energy of τ-MnAl and interface energy of τ-MnAl/Fe(Co) films, respectively. Their magnetic coupling interactions were investigated by varying the Fe(Co) atomic layer numbers. It is noted that both Fe and Co exhibited ferromagnetic coupling with τ-MnAl. Interestingly, an unusual oscillation phenomenon of magnetic coupling for τ-MnAl with Fe(Co) atomic layers was observed depending on the layer thickness of Fe(Co). Moreover, Fe and Co showed different oscillation modes. The energy difference between antiferromagnetic and ferromagnetic states is larger for τ-MnAl/Fe and τ-MnAl/Co when the Fe(Co) layer numbers are even and odd, respectively. Their mechanisms were analyzed based on the band structures and the confinement of electrons in quantum wells. It is found that the magnetic coupling oscillation in τ-MnAl/Fe originated from both the spin up Δ1 band and spin down Δ5 band at the [capital Gamma, Greek, macron] points. Comparatively, the oscillation of τ-MnAl/Co is due to the spin up band at the X[combining macron] point. The present results could provide insight to further understand interfacial exchange interactions among magnetic layers.

The effect of magnetic field on perturbation evolution in homogeneously sheared flows

The goal of this paper is to identify and characterize the fundamental mechanisms that contribute toward flow stabilization in sheared plasma flows. Toward that end, we investigate the evolution of velocity and magnetic field perturbations in homogeneously sheared magnetohydrodynamic (MHD) flows subjected to an imposed streamwise magnetic field. The influences of magnetic field strength ($B_{0}$) and perturbation wavevector orientation ($\unicode[STIX]{x1D6FD}$) are characterized using linear analysis and direct numerical simulations. The linear analysis of ideal MHD indicates that the perturbation evolution is governed by four processes: pressure redistribution, kinetic energy production, kinetic–magnetic energy exchange and magnetic energy production due to magnetic stretching. The interplay between these processes can be characterized by the ratio of shear-to-magnetic timescales ($R_{A}\equiv V_{A}\unicode[STIX]{x1D705}/S$) and $\unicode[STIX]{x1D6FD}$, where $V_{A}$, $\unicode[STIX]{x1D705}$ and $S$ are Alfvén wave speed, initial wavenumber and mean flow shear, respectively. For cases with low values of $\boldsymbol{R}_{\boldsymbol{A}}~(\ll \mathbf{1})$, a three-stage perturbation evolution is seen. At the first stage, pressure redistribution and production dominate leading to hydrodynamic-type behaviour. In the second stage, the onset of magnetic stretching process leads to an increase in magnetic energy. At late stages, production subsides and the dynamics is dominated by harmonic exchange between velocity and magnetic fields. For cases of $\boldsymbol{R}_{\boldsymbol{A}}\approx \mathbf{1}$, the magnetic field reacts rapidly enough that hydrodynamic and magnetic production stages occur simultaneously followed by harmonic exchange. In the case of $\boldsymbol{R}_{\boldsymbol{A}}\gg 1$, all three stages occur simultaneously leading to harmonic exchange between kinetic and magnetic energies without any perturbation growth. For all cases considered, the late stage harmonic exchange results in equipartition between perturbation magnetic and kinetic energies. For a given $R_{A}$, the effect of increasing $\unicode[STIX]{x1D6FD}$ is to reduce the intensity of coupling and progressively slow down the three stages of evolution. For spanwise wavevector perturbations, the velocity–magnetic field interaction mechanism vanishes and there is no effect of pressure or magnetic field on individual velocity components.

Ultrafine nanocrystalline NdFeB prepared by cryomilling with HDDR process

In this work, the NdFeB ribbons (Nd13.5Fe73Co7·5B6) were first subjected to the hydrogenation disproportionation (HD) to prepare disproportionation NdFeB precursor and subsequently cryomilled for different times. The submicron NdFeB particles with ultrafine nanocrystalline were finally obtained after desorption recombination (DR) process. The results indicated that with the increase of the cryomilling time, Nd2Fe14B grains were refined to nanoscale, but the coercivity decreased due to the strong exchange coupling between the nano-grains. The optimized nanocrystalline NdFeB particles have a size of 40 nm or less and present a coercivity of 6.63 kOe after cryomilling for 10 h followed by DR treatment at 800 °C for 10 min. To further improve the magnetic properties, Ca was added into HD powders in the course of cryomilling process to protect the powders from oxidation and a noticeable coercivity of 9.49 kOe was obtained. Finally, the mechanism of magnetic interactions and coercivity enhancement were discussed.

Crystal structure and magnetic properties of Ti-doped Bi0.84La0.16FeO3 at morphotropic phase boundary

We have studied the crystal structure and magnetic properties of Bi0.84La0.16Fe1-xTixO3 (x = 0.02–0.1) at the morphotropic phase boundary of R3c, Imma, and Pbam phases. The results of Rietveld-refined X-ray diffraction patterns reveal the existence of multi-phase structures, including R3c + Imma for x = 0.02–0.06 and Imma + Pbam for x = 0.08–0.1. The studies of Raman scattering spectra indicate a structural transformation through the disappearance of typical R3c modes. This strongly influences the magnetic properties that are dependent on the crystalline phase ratio. In particular, the magnetic coercivity of x = 0.04–0.06 drastically changes when the Imma phase is dominant. A mechanism of magnetic interactions occurring at the phase boundary is proposed to explain the features of magnetic hysteresis loops of the compounds.

Effects of Mn Ion Implantation on XPS Spectroscopy of GaN Thin Films

Gallium nitride (GaN) thin film was deposited onto a sapphire substrate and then implanted with 250 keV Mn ions at two different doses of 2 × 1016 ions/cm2 and 5 × 1016 ions/cm2. The as-grown and post-implantation-thermally-annealed samples were studied in detail using x-ray photoelectron spectroscopy (XPS). The XPS peaks of Ga 3d, Ga 2p, N 1s, Mn 2p and C 1s were recorded in addition to a full survey of the samples. The doublet peaks of Ga 2p for pure GaN were observed blue-shifted when compared with elemental Ga, and appeared further shifted to higher energies for the implanted samples. These observations point to changes in the bonds and the chemical environment of the host as a result of ion implantation. The results revealed broadening of the N 1s peak after implantation, which is interpreted in terms of the presence of N-Mn bonds in addition to N-Ga bonds. The XPS spectra of Mn 2p recorded for ion-implanted samples indicated splitting of Mn 2p 1/2 and Mn 2p 3/2 peaks higher than that for metallic Mn, which helps rule out the possibility of clustering and points to substitutional doping of Mn. These observations provide a framework that sheds light on the local environment of the material for understanding the mechanism of magnetic exchange interactions in Mn:GaN based diluted magnetic semiconductors.

Transformation from conducting ferromagnetic to insulating diamagnetic in vanadium doped ZnO nanoparticles

A simple cost effective approach of solution combustion method is chosen to prepare the vanadium doped ZnO nanoparticles. X-ray diffraction and Raman spectroscopy affirm the single phase formation of ZnO and evolution of secondary phase upon increasing vanadium concentration. Further lattice irregularity due to vanadium substitution is clearly manifested. Morphological aspects explored using SEM and TEM implies the alteration of hexagonal grain boundaries to spherical ones. A systematic study on the grain boundary reformation of the ZnO nanograins due to vanadium is undertaken using structural, morphological and spectroscopic characterizations. Electrical studies illustrate the individual contributions of grain and grain boundary towards the resistance of the material. Magnetization decreases with increasing vanadium concentration. Possible interplay between defect/doping and conductivity is proposed so as to explain the underlying mechanism of magnetic interactions.

Effect of washing process on the magnetic properties of Nd-Fe-B nanoparticles prepared by reduction-diffusion method

Nd-Fe-B nanoparticles with a particle size below 50nm and excellent magnetic properties were obtained via a novel route which makes use of both spray drying and reduction-diffusion processes. Uniform Nd-Fe-B particles were formed by the optimization of Ca amount as a reducing agent and additional washing by milling in ethanol media. Especially, we implemented a two-step washing process which contributed to the excellent magnetic properties with high remanence and coercivity. After the removal of CaO by novel washing process, the maximum energy product (BH)max of the particles showed 22.1MGOe. This value is superior to those reported in reduction-diffusion process. We used Henkel plot to assume the mechanism of magnetic interactions of the Nd-Fe-B nanoparticles.

Transition Metal Adsorbed-Doped ZnO Monolayer: 2D Dilute Magnetic Semiconductor, Magnetic Mechanism, and Beyond 2D.

As an improvement over organic or inorganic layered crystals, the synthetic monolayer ZnO(M) inherits semiconductivity and hostability from its bulk, yet it acts as a promising host for dilute magnetic semiconductors. Here, we report the electronic and magnetic properties of ZnO(M) doped with one 3d transition metal ion and simultaneously adsorbed with another 3d transition metal ion. Two sequences are studied, one where the dopant is fixed to Mn and the adsorbate is varied from Sc to Zn and another where the dopant and adsorbate are reversed. First-principles results show that the stable adsorbed−doped systems possess a lower bandgap energy than that of the host. System magnetic moments can be tuned to |5 – x|μB, where x refers to the magnetic moment of the individual 3d atom. An interplay between superexchange and direct exchange yields a ferromagnetic system dually adsorbed−doped with Mn. In addition to a novel material design route, the magnetic interaction mechanism is found beyond two dimensions, having been identified for its three-dimensional bulk and zero-dimensional cluster counterparts.