Theoretical characterization of the temperature-dependent saturation magnetization of magnetic metallic materials

Based on the force-heat equivalence energy density principle,a theoretical model for magnetic metallic materials is developed,which characterizes the temperature-dependent magnetic anisotropy energy by considering the equivalent relationship between magnetic anisotropy energy and heat energy;then the relationship between the magnetic anisotropy constant and saturation magnetization is considered.Finally,we formulate a temperature-dependent model for saturation magnetization,revealing the inherent relationship between temperature and saturation magnetization.Our model predicts the saturation magnetization for nine different magnetic metallic materials at different temperatures,exhibiting satisfactory agreement with experimental data.Additionally,the experimental data used as reference points are at or near room temperature.Compared to other phenomenological theoretical models,this model is considerably more accessible than the data required at 0 K.The index included in our model is set to a constant value,which is equal to 10/3 for materials other than Fe,Co,and Ni.For transition metals(Fe,Co,and Ni in this paper),the index is 6 in the range of 0 K to 0.65T_(cr)(T_(cr) is the critical temperature),and 3 in the range of 0.65T_(cr) to T_(cr),unlike other models where the adjustable parameters vary according to each material.In addition,our model provides a new way to design and evaluate magnetic metallic materials with superior magnetic properties over a wide range of temperatures.

Research Progress and Prospects of Magnetic Nanomaterials

Nanomaterials are one of the research and development hotspots in the field of cutting-edge new materials,and also an important strategic emerging industry.Magnetic nanomaterials have broad application prospects in fields such as chemical engineering,new materials,electronic information,and biomedicine.This article introduces the application progress and preparation methods of magnetic nanomaterials,and puts forward suggestions for further optimizing the preparation process of magnetic nanomaterials and developing new magnetic materials with better performance.

Research progress of permanent ferrite magnet materials

Permanent ferrite magnet materials are extensively employed due to their exceptional magnetic properties and cost-effectiveness.The fast development in electromobile and household appliance industries contributes to a new progress in permanent ferrite materials.This paper reviews the deveolpement and progress of permanent ferrite magnet industry in recent years.The emergence of new raw material,the advancement of perparation methods and manufacturing techniques,and the potential applications of permanent ferrite materials are introduced and discussed.Specifically,nanocrystallization plays a crucial role in achieving high performance at a low cost and reducing reliance on rare earth resources,and therefore it could be a promising development trendency.

Leveraging Quantum Computing for the Ising Model to Simulate Two Real Systems: Magnetic Materials and Biological Neural Networks (BNNs)

Quantum computing is a field with increasing relevance as quantum hardware improves and more applications of quantum computing are discovered. In this paper, we demonstrate the feasibility of modeling Ising Model Hamiltonians on the IBM quantum computer. We developed quantum circuits to simulate these systems more efficiently for both closed and open boundary Ising models, with and without perturbations. We tested these various geometries of systems in both 1-D and 2-D space to mimic two real systems: magnetic materials and biological neural networks (BNNs). Our quantum model is more efficient than classical computers, which can struggle to simulate large, complex systems of particles.

Magnetic and magnetocaloric effect of Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass

Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity(RC)was reported.Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K.In addition,we find that the magnetic entropy change(-△S_(M))originates from the sample undergoing a ferromagnetic(FM)to paramagnetic(PM)transition around 20 K.Under a field change from 0 T to 7 T,the value of maximum magnetic entropy change(-△S_(M)^(max))reaches 12.5 J/kg·K,and the corresponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K.The large RC and wide temperature range make the Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass be a promising material for application in magnetic refrigerators.

Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.

Recent progress in high temperature permanent magnetic materials

Permanent magnetic materials capable of operating at high temperature up to 500℃ have wide potential applications in fields such as aeronautics, space, and electronic cars. SmCo alloys are candidates for high temperature applications, since they have large magnetocrystalline anisotropy field （6-30 T）, high Curie temperature （720-920℃）, and large energy product （〉200 kJ.m-3） at room temperature. However, the highest service temperature of commercial 2：17 type SmCo magnets is only 300℃, and many efforts have been devoted to develop novel high temperature permanent magnets. This review focuses on the development of three kinds of SmCo based magnets： 2：17 type SmCo magnets, nanocrystalline SmCo magnets, and nanocomposite SmCo magnets. The oxidation protection, including alloying and surface modification, of high temperature permanent magnets is discussed as well.

Metal magnetic memory testing for early damage assessment in ferromagnetic materials

In order to investigate the physical mechanism of metal magnetic memory testing, both the influences of earth magnetic field and applied stress on magnetic domain structure were discussed. Static tension and fatigue tests for low carbon steel plate specimens were carried out on hydraulic servo testing machine of MTS810 type and magnetic signals were measured during the processes by the type of EMS-2003 instrument. The results indicate that the initial magnetic signals of specimens are different before loading. The magnetic signals curves are transformed from initial random to regular pattern due to the effect of two types of loads. However, the shape and distribution of magnetic signal curves in the elastic region are different from that of plastic region in tension test. While in fatigue test those magnetic signals curves corresponding to different cycles are similar. The H_p(y) value of magnetic signals on the fracture zone increases dramatically at the breaking transient time and positive-negative magnetic poles occur on the two parts of fracture zone.

Synthesis and measurement of structural and magnetic properties of K-doped LaCoO_3 perovskite materials

Polycrystalline La1-xKxCoO3 （0≤ x ≤ 0.2） rare earth cobaltates have been synthesized by a solution combustion method using glycine as a fuel. The synthesized ceramic materials were characterized by powder X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FTIR）, and magnetic measurements and studied for physical properties, such as photoeatalytic activity. FTIR measurements in conjunction with XRD showed that phases beyond 10% K doping are accompanied by small amounts of impurities. Chemical titrations show the presence of Co^4＋ and account for the Co^3＋-Co^4＋ mixed-valency of the system. The parent LaCoO3 shows spin-glass transition at low temperatures, whereas doped samples show transition from spin-glass behavior to paramagnetic ordering on progressive doping of K. ＂Mixed-conductor＂ nature of these ceramics positions them as viable candidates for solid oxide fuel cell （SOFC） applications.

Thermo-magnetic analysis of thick-walled spherical pressure vessels made of functionally graded materials

This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressure vessel is subject to axisymmetric mechanical and thermal loadings within a uniform magnetic field. The material properties of the FGM are considered as the power-law distribution along the thickness. Navier’s equation, which is a second-order ordinary differential equation, is derived from the mechanical equilibrium equation with the consideration of the thermal stresses and the Lorentz force resulting from the magnetic field. The distributions of the displacement, strains, and stresses are determined by the exact solution to Navier’s equation. Numerical results clarify the influence of the thermal loading, magnetic field, non-homogeneity constant, internal pressure, and angular velocity on the magneto-thermo-elastic response of the functionally graded spherical vessel. It is observed that these parameters have remarkable effects on the distributions of radial displacement, radial and circumferential strains, and radial and circumferential stresses.

Magnetically responsive porous materials for efficient adsorption and desorption processes

Magnetically responsive porous materials possess unique properties in adsorption processes such as magneticinduced separation and heat generation in alternating magnetic fields, which greatly facilitates recycling procedures, favors long-term operation, and improves desorption rate, making conventional adsorption processes highly efficient. With increasing interest in magnetic adsorbents, great progress has been made in designing and understanding of magnetically responsive porous materials varying from monoliths to nanoscale particles used for adsorption including oil uptake, removal of hazardous substances from water, deep desulfurization of fuels, and CO2 capture in the past few years. Therefore, a review summarizing the advanced strategies of synthesizing these magnetically responsive adsorbents and the utilization of their magnetism in practical applications is highly desired. In this review, we give a comprehensive overview of this emerging field, highlighting the strategies of exquisitely incorporating magnetism to porous materials and subtly exploiting their magnetic responsiveness. Further innovations for fabricating or utilizing magnetic adsorbents are expected to be fueled. The potential opportunities and challenges are also discussed.

Electrochromic & magnetic properties of electrode materials for lithium ion batteries

Progress in electrochromic lithium ion batteries （LIBs） is reviewed, highlighting advances and possible research di- rections. Methods for using the LIB electrode materials＇ magnetic properties are also described, using several examples. Li4Ti5Ol2 （LTO） film is discussed as an electrochromic material and insertion compound. The opto-electrical proper- ties of the LTO film have been characterized by electrical measurements and UV-Vis spectra. A prototype bi-functional electrochromic LIB, incorporating LTO as both electrochromic layer and anode, has also been characterized by charge- discharge measurements and UV-Vis transmittance. The results show that the bi-functional electrochromic LIB prototype works well. Magnetic measurement has proven to be a powerful tool to evaluate the quality of electrode materials. We introduce briefly the magnetism of solids in general, and then discuss the magnetic characteristics of layered oxides, spinel oxides, olivine phosphate LiFePO4, and Nasicon-type Li3Fez（PO4）3. We also discuss what kind of impurities can be detected, which will guide us to fabricate high quality films and high performance devices.

Study on Vector Magnetic Properties of Magnetic Materials Using Hybrid Hysteresis Model

This paper presents a method to study the vector magnetic properties of magnetic materials under alternating and rotational magnetic field using 2-D vector hybrid hysteresis model.Combining Preisach model and Stoner-Wohlfarth(S-W)model,the vector hybrid hysteresis model is established for magnetic materials.The alternating and rotational hysteresis properties are calculated under different excitation frequency,respectively.And the computed results are compared with the experimental measurement ones.It is shown that the vector model can simulate the alternating and rotational magnetic properties effectively under low magnetization fields and low excitation frequency.

Hopkinson Effect in Soft Magnetic Materials

The μi-T curves of the alloy Fe73.5Cu1 Nb3Si13.5B9 in the amorphous state and in the nanocrys-talline state have been investigated. For comparison, μi-T curves of the other two kinds of typical soft magnetic alloys also have been measured. It was found that a sharp Hopkinson peak appeared at the Curie point for each amorphous and crystalline alloy but there was no Hopkinson peak for the nanocrystalline alloy at the Curie point of the residual amorphous phase. This phenomenon has been explained in terms of the characteristic temperature dependence of the effective magnetic anisotropy.

Magnetic two-dimensional van derWaals materials for spintronic devices

Magnetic two-dimensional(2D)van derWaals(vdWs)materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin,charge,and energy valley,which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future.This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress.Next,the proximity-effect,current-induced magnetization switching,and the related spintronic devices(such as magnetic tunnel junctions and spin valves)based on magnetic 2D vdWs materials are presented.Finally,the development trend of magnetic 2D vdWs materials is discussed.This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.

Development of magnetocaloric materials in room temperature magnetic refrigeration application in recent six years

Some magnetocaloric materials were used successfully in magnetic refrigeration application and became one of the critical parts of magnetic refrigeration technology whose delightful progresses were made worldwide in the past 30 years. At the same time, the research on giant magnetocaloric materials will accelerate the development of room temperature magnetic refrigeration. In this paper, the new theoretical and experimental investigations on magnetic materials in room temperature application were described, including Gd and its binary and ternary intermetallic compounds, Mn-based compounds, La(Fe13-xMx)-based compounds and manganites. Based on the analysis of hysteresis, corrosion, cost and heat process, the comparison between different families of magnetic materials was discussed. Further research of room temperature magnetic refrigerant was suggested.

Study on Gd-Al-Dy System Magnetic Refrigeration Materials

d-Al-Dy system materials were prepared by the technique of powder sintering. Twolayers gradient function materials with compositions of (Gd_0.9Dy_0.1)_3Al_2 and Gd_3Al_2 respectively were studied. The results show that the Curie temperature (Tc) of the monolayer material decreases with the increment of Dy content. The Tc values of the twolayer gradient function material agree well with the layer numbers and corresponding to Dy content. For the Tc gradiently changed twolayers Gd-Al-Dy system material, its ΔSm changes smoothly with temperature. Therefore, the magnetic refrigeration is improved.

Relationship between magnetic Barkhausen noise and the stresses, the hardness and the phase content of ferromagnetic materials

Magnetic Barkhausen Noise (MBN) is a phenomenon of electromagnetic energy emission due to the movement of magnetic domain walls inside ferromagnetic materials when they are locally magnetized by an alternating magnetic field. According to Faraday’s law of electromagnetic induction, the noise can be received by the coil attached to the surface of the material being magnetized and the noise carries the message of the characteristics of the material such as stresses, hardness, phase content, etc. Based on the characteristic of the noise, research about the relationship between the welding stresses in the welding assembly and the noise, the fatigue damage of the plate structure and the noise, and the influence of heat treatment and the variation of phase content to the noise are carried out in this paper.

Thermodynamical Evaluation on Magnetocaloric Effect of Magnetic Refrigerating Materials Near Room Temperature

The relationship between isothermal magnetic entropy change DELTA S andadiabatic temperature change DELTA T_(ad) was deduced according to the principles of thermodynamics.The MCE and the engineering application were discussed for Gd and several new kinds of magneticrefrigerating materials near room temperature, Gd_5Si_2Ge_2, MnFeP_(0.45)As_(0.55) and LaFe_(11.2)Co_(0.7)Si_(1.1). Isothermal entropy change is proportional to adiabatic temperature change with afactor of T/C (T is temperature, C is heat capacity). When the comparison of magnetacoloric effectis made for two different materials, we should consider isothermal entropy change as well asadiabatic temperature change.

MATHEMATICAL MODELS ARISING FROM A SURVEY OF FERROMAGNETIC MATERIALS UNDER MAGNETISATION

This paper focuses on mathematical models describing the mechanical behavior of ferromagnetic materials under magnetization. Through combination of the electromagnetic field theory with the theory of elastic mechanics, several nonlinear systems of fourth order partial differential equations were deduced. By making further assumption, the first-order approximation of the above equations was established, of which the solutions are good enough for engineering application.