New Type Of Magnetic Research Articles

Experimental Evidence for a New Type of Magnetism

Experimental Evidence for a New Type of Magnetism

Toward 2D Magnets in the (MnBi2 Te4 )(Bi2 Te3 )n Bulk Crystal.

2D magnets and their engineered magnetic heterostructures are intriguing materials for both fundamental physics and application prospects. On the basis of the recently discovered intrinsic magnetic topological insulators (MnBi2 Te4 )(Bi2 Te3 )n , here, a new type of magnet, in which the magnetic layers are separated by a large number of non-magnetic layers and become magnetically independent, is proposed. This magnet is named as a single-layer magnet, regarding the vanishing interlayer exchange coupling. Theoretical calculations and magnetization measurements indicate that, the decoupling of the magnetic layers starts to emerge from n = 2 and 3, as revealed by a unique slow-relaxation behavior below a ferromagnetic-type transition at Tc = 12-14 K. Magnetization data analysis shows that the proposed new magnetic states have a strong uniaxial anisotropy along the c-axis, forming an Ising-type magnetic structure, where Tc is the ordering temperature for each magnetic layer. The characteristic slow relaxation, which exists only along the c-axis but is absent along the ab plane, can be ascribed to interlayer coherent spin rotation and/or intralayer domain wall movement. The present results will stimulate further theoretical and experimental investigations for the prototypical magnetic structures, and their combination with the topological surface states may lead to exotic physical properties.

The model of an anomaly detector for HiLumi LHC magnets based on Recurrent Neural Networks and adaptive quantization

This paper focuses on an examination of an applicability of Recurrent Neural Network models for detecting anomalous behavior of the CERN superconducting magnets. In order to conduct the experiments, the authors designed and implemented an adaptive signal quantization algorithm and a custom Gated Recurrent Unit-based detector and developed a method for the detector parameters selection.Three different datasets were used for testing the detector. Two artificially generated datasets were used to assess the raw performance of the system whereas the dataset intended for real-life experiments and model training was composed of the signals acquired from a new type of magnet, to be used during High-Luminosity Large Hadron Collider project. Several different setups of the developed anomaly detection system were evaluated and compared with state-of-the-art One Class Support Vector Machine (OC-SVM) reference model operating on the same data. The OC-SVM model was equipped with a rich set of feature extractors accounting for a range of the input signal properties.It was determined in the course of the experiments that the detector, along with its supporting design methodology, reaches F1 equal or very close to 1 for almost all test sets. Due to the profile of the data, the setup with the lowest maximum false anomaly length of the detector turned out to perform the best among all five tested configuration schemes of the detection system. The quantization parameters have the biggest impact on the overall performance of the detector with the best values of input/output grid equal to 16 and 8, respectively. The proposed solution of the detection significantly outperformed OC-SVM-based detector in most of the cases, with much more stable performance across all the datasets.

Uniform transverse beam profile with a new type of nonlinear magnet**Supported supported by National Natural Science Foundation of China (11175195)

In this paper, a new type of magnet is proposed and produced to give a uniform transverse beam profile. Compared to octupole magnets, the new type of magnet can provide a similar octupole magnet field in the middle, but the rise rate declines quickly at the edges, so that a beam of the same uniformity is obtained with less particle loss. Besides that, a mechanical structure is added to adjust the width of the middle region to satisfy different transverse dimensions, which would further reduce particle loss. Some numerical simulations have been done with the octupole and the new type of magnet to show the advantages of the new magnet.

Magnetic Flux Density Distribution in the Air Gap of a Ferromagnetic Core With Superconducting Blocks: Three-Dimensional Analysis and Experimental NMR Results

The design of magnetic cores can be carried out by taking into account the optimization of different parameters in accordance with the application requirements. Considering the specifications of the fast field cycling nuclear magnetic resonance (FFC-NMR) technique, the magnetic flux density distribution, at the sample insertion volume, is one of the core parameters that needs to be evaluated. Recently, it has been shown that the FFC-NMR magnets can be built on the basis of solenoid coils with ferromagnetic cores. Since this type of apparatus requires magnets with high magnetic flux density uniformity, a new type of magnet using a ferromagnetic core, copper coils, and superconducting blocks was designed with improved magnetic flux density distribution. In this paper, the designing aspects of the magnet are described and discussed with emphasis on the improvement of the magnetic flux density homogeneity $(\Delta B/B_0)$ in the air gap. The magnetic flux density distribution is analyzed based on 3-D simulations and NMR experimental results.

Spin Density Wave Driven by Quadrupolar Kondo Effect in Two-Channel Kondo Lattice

A new type of magnetism is found in the two-channel Kondo lattice where each non-Kramers doublet is coupled with two conduction bands by the orbital exchange J . The quadrupolar Kondo effect leads to an SDW state in the case of quarter filled bands, i.e., one conduction electron per site. This order is understood from the strong coupling limit with respect to J . Using the continuous-time Monte Carlo method combined with the DMFT at finite temperature T , the phase diagram is constructed in the J – T plane for the quarter filled case.

Recent developments in the formation and structure of tin–iron oxides by laser pyrolysis

Complex oxides demonstrate specific electric and magnetic properties which make them suitable for a wide variety of applications, including dilute magnetic semiconductors for spin electronics. A tin–iron oxide Sn 1− x Fe x O 2 nanoparticulate material has been successfully synthesized by using the laser pyrolysis of tetramethyl tin–iron pentacarbonyl–air mixtures. Fe doping of SnO 2 nanoparticles has been varied systematically in the 3–10 at% range. As determined by EDAX, the Fe/Sn ratio (in at%) in powders varied between 0.14 and 0.64. XRD studies of Sn 1− x Fe x O 2 nanoscale powders, revealed only structurally modified SnO 2 due to the incorporation of Fe into the lattice mainly by substitutional changes. The substitution of Fe 3+ in the Sn 4+ positions (Fe 3+ has smaller ionic radius as compared to the ionic radius of 0.69 Å for Sn 4+) with the formation of a mixed oxide Sn 1− x Fe x O 2 is suggested. A lattice contraction consistent with the determined Fe/Sn atomic ratios was observed. The nanoparticle size decreases with the Fe doping (about 7 nm for the highest Fe content). Temperature dependent 57Fe Mössbauer spectroscopy data point to the additional presence of defected Fe 3+-based oxide nanoclusters with blocking temperatures below 60 K. A new Fe phase presenting magnetic order at substantially higher temperatures was evidenced and assigned to a new type of magnetism relating to the dispersed Fe ions into the SnO 2 matrix.

Numerical analysis of influences of casting speeds on fluid flow in funnel shape mould with new type EMBr

In present work, a new type of magnet specially designed for the thin slab casting funnel shape mould is adopted. Numerical simulations of the new type electromagnetic brake (EMBr) influences on flow field are carried out. For the computation of magnetic fields, the software ANSYS with finite element method is adopted. For fluid flow, commercial software FLUENT with finite volume method is used to predict steel flow with EMBr, and magnetohydrodynamics model is activated to couple the applied magnetic and flow field. The variation of electromagnetic parameters are studied with the casting speed changing from 5 to 6 m min–1. The results show that, the flow field can be significantly controlled by the new type EMBr. Furthermore, an increase of ∼1000 A n ampere turns is needed to produce larger enough magnetic flux density in the mould region to control the fluid flow for every increment 0·5 m min–1 of casting speed.

Electromagnetic Brake Effects on the Funnel Shape Mold of a Thin Slab Caster Based on a New Type Magnet

In the present work, a new type of magnet specially designed for the thin slab casting funnel shape mold is developed. The unique feature of the new type of magnet lies in the fact that, the inner surfaces of the new magnet facing the mold are irregular to fit the complex funnel shape, while the inner surfaces of the convential magnet are planar. Magnetic fields produced by both the new type and the conventional magnets are computed under the same number of ampere turns for comparison. Keeping the position of the magnet relative to the mold fixed, numerical simulations of the influence of the new and conventional type magnets on the flow field in the mold are made. The commercial software FLUENT is used to predict the behavior of electrically conducting fluid flow under the influence of static magnetic fields. For the computation of magnetic fields, the finite element method (FEM) is adopted, while for fluid flow, the finite volume method (FVM) based on structured body fitted coordinate grids is used. The results show that the new type of magnet can produce larger magnetic flux density in the mold region than the conventional one does with the same current intensity. For the funnel shape mold, the electromagnetic brake (EMBr) due to the new magnet can provide a more uniform downstream velocity profile than that due to the conventional magnet, and almost 40 pct reduction in ampere turns; this fact implies that a lot of electrical energy could be saved.

Tailoring the induced magnetism in carbon-based and non-traditional inorganic nanomaterials

Results of computer simulations based on ab initio methods are presented for the newly observed magnetism found in carbon-based and non-traditional inorganic materials. These results reinforce our previously proposed explanation about the nature and the origin of this "new type of magnetism" which attributes this to electron correlations effects which develop in the presence of defects and doping. These observations suggest possible pathways which can be used to tailor such a defect-induced magnetism with significant implications in nanotechnology.

Quantum spin flop transition in nanowire ferrimagnets

Recently a ferrimagnetic quantum spin chain consisting of Ni and Mn ions has been synthesized to create a new type of magnet with a long life time, based on the Glauber's slow dynamics. Its magnetic properties are well described by the ( s , S ) = ( 1 , 2 ) spin alternating chain model, with single-ion anisotropies D 1 and D 2 at Ni and Mn sites, respectively. Thus we investigate the magnetization process of this model, using the numerical exact diagonalization and finite-size scaling technique. It predicts a new field-induced quantum phase transition between two different Tomonaga–Luttinger liquid phases; TLL1 and TLL2 for some negative values of D 1 and D 2 . This transition corresponds to a quantum version of the spin flop. Some typical phase diagrams are presented.

New pulsed-magnets for 100 T, long-pulse and diffraction measurements

Development of non-destructive pulsed magnet aiming at 100 T-generation beyond 80 T-field is our mission. For that purpose, we have been developing a new coil system, socalled "dual coil system" and succeeded in generation of 85 T. This magnet will open the nondestructive 100 T-field in the near future. New type of magnet with longer pulse duration also has been developed. This magnet has a gap between the inner coil and the outer one where liquid nitrogen can flow. Therefore, the magnet can be cooled down by liquid nitrogen rapidly. The repetition time has been reduced to 15 minutes for 60 T-field with the duration of about 30 msec. By means of this rapid-cooling technique, a magnet for X-ray diffraction measurement has been made. This magnet consists of split coils with a split gap of 5 mm and a duration time of about 30 msec. This magnet allows us to carry out X-ray diffraction measurement under pulsed high field. The maximum field of the magnet is found to be 38 T, which is limited by utilized energy of the capacitor bank.

Development of Magnetic Force-Assisted New Gene Transfer System Using Biopolymer-Coated Ferromagnetic Nanoparticles

Development of a simple method for converting the lipid envelope of an inactivated virus to a gene transfer vector was achieved a couple years ago in the medical school of Osaka University. Hemagglutinating virus of Japan (HVJ; Sendai virus) envelope (HVJ-E) vector was constructed by incorporating plasmid DNA into inactivated HVJ particles. This HVJ envelope vector introduced plasmid DNA efficiently and rapidly into various cell lines, including cancer cells and several types of primary cell culture. In the present study, efficiency of gene transfer was found to be greatly enhanced by application of a magnetic field. Therefore, we developed a new type of magnet for magnetically enhancing and targeting gene transfection system by using vectors associated with ferromagnetic particles coated with positively/negatively charged biopolymers, which can help to enhance and target gene delivery with higher efficiency. For the transfection experiment in vitro, the HVJ-E vector was mixed with ferromagnetic particles coated with biopolymer and this mixture was added to cultured cells which were set up under the permanent magnet. The effect of the dose of the ferromagnetic particles on the transfection efficiency was discussed. In order to clarify the effect of magnetic field gradient on the accumulation possibility of the magnetic particles and the accuracy of the targeted site in the blood vessels, calculation of the applied magnetic force for the ferromagnetic particles inside the blood vessel was also performed

Surprising electronic–magnetic properties of closed packed organized organic layers

Cooperative effects generate new electronic and magnetic properties in closed packed organized organic layers. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin specific electron transmission. For many thiolated molecules self-assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism that is caused by the formation of closed packed layers of organic molecules on metal. In particular, charge transfer occurs between the substrate and the adsorbed layer. This charge is responsible for the appearance of magnetism.

New electronic and magnetic properties of monolayers of thiols on gold

AbstractNew electronic and magnetic properties are induced by the adsorption of close‐packed monolayers of thiols on gold. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin‐specific electron transmission. For many thiolated molecules self‐assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism, induced by the formation of a closed packed layer of organic molecules on metal. The adsorption results in charge transfer between the substrate and the adsorbed layer, which is the origin of this magnetism.

異方性Ｎｄ‐Ｆｅ‐Ｂ系フレキシブルボンド磁石の作製とモータへの適用

Isotropic Nd-Fe-B-based ring-shaped resin-bonded magnets have been generally used in small motors and actuators for PCs and their peripherals. However, development of a new type of magnet with superior magnetic properties is essential for a further reduction of the size of such motors. Although usage of anisotropic Nd-Fe-B powder made by the HDDR process is a promising method of preparing anisotropic magnets to replace the conventional isotropic magnets, its high coercivity of over 1.2 MA/m, which is required for thermal stability of the magnetic flux comparable with that of conventional isotropic Nd-Fe-B magnets, makes it difficult to magnetize the prepared magnets. Therefore, magnets prepared from anisotropic HDDR powder have not been used to create ring-shaped magnets for small motors up to now. To overcome the above difficulty, we developed a new technology that makes it possible to prepare axially oriented ring-shaped magnets for small motors. This paper reports a method of preparing axially oriented ring-shaped magnets for small motors from anisotropic HDDR powder. To use this process, it is possible to product an anisotropic Nd-Fe-B-based flexible bonded magnet. These flexible bonded magnets are able to keep a high efficiency, like a radially oriented magnet. And, their magnet powders are covered with elastomer.

Possibility of type II magnetism in some mixed magnets and spin glasses

A phenomenological Ginzburg-Landau free energy is introduced to describe mixed magnets or spin glasses with two order parameters, the bulk magnetisation and the spin glass order parameter. The susceptibility has a cusp at the onset of the spin glass phase. To the two order parameters are associated two coherence lengths and, depending on their ratio, two types of mixed magnetic states can occur: (i) the conventional mixed magnetism with macroscopic domains, and (ii) a new type of magnetism for which the energy of the domain walls becomes negative, in strong analogy with type II superconductivity. It is argued that MnSi and the alloys PdMn and PdFe in limited ranges of concentration are magnets of the second type.