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Permanent magnets produce magnetic fields and maintain the field even in the presence of an opposing magnetic field. They are widely used in electric machines, electronics, and medical devices. Part I reviews the conventional manufacturing processes for commercial magnets, including Nd-Fe-B, Sm-Co, alnico, and ferrite in cast and sintered forms. In Part II, bonding, emerging advanced manufacturing processes, as well as magnet recycling methods are briefly reviewed for their current status, challenges, and future directions.

Samarium-cobalt alloys are used in some of the strongest permanent magnets, particularly for applications between about 200 and 550°C, but the utilization of these materials is restricted by their brittleness. Improving their mechanical resilience would allow them to be used more widely and, in some cases, substitute for neodymium-based magnet alloys which are subject to supply-chain risks. We have engineered a series of novel microstructures with bi-modal grain size distributions to achieve unprecedented combinations of mechanical and magnetic properties. Improvements up to 73% are obtained in the flexural strength of Sm2(CoFeCuZr)17 sintered magnets, with negligible impact on the magnetic properties. Our mechanically-robust, high-performance Sm-Co magnets are made without changing the chemical compositions of the materials or their heat treatment procedures, making them highly compatible with existing manufacturing processes.

The Stoner-Wohlfarth is the most used model of magnetic hysteresis, but its computation is time-consuming. We use machine learning to approximate piecewise this model by easy-to-compute analytic functions. Our parametrization is suitable for fast quantitative evaluations and fitting experimental data, which we exemplify., Comment: 5 pages, 4 figures

Hall effect sensors are used widely in areas including position sensing, DC current transformers, and fuel level indicator due to their low costs, high reliability, free of contact bounce, and immune to environmental contaminants [1]. However, the lower measuring accuracy and sensitivity comparing to fluxgate magnetometers limit their application. Improving the sensitivity becomes a crucial issue for Hall effect sensor. The key factor determining sensitivity of Hall effect sensor is high electron mobility. Therefore, GaAs and InAs are often used [2]. Recently, topological insulators (TIs) are discovered with an ultra-high surface conductivity [3]. Unlike normal semiconductor, TIs have gapless surface states, protected by time reversal symmetry, inside the bulk band gap, which prohibits the backscattering on non-magnetic impurities. The surface state of TIs can be broken by introducing magnetic impurities. Magnetic impurities lead to a small surface band gap which can induce phenomena such as the quantum anomalous Hall effect (AHE) [4]. All above features enable TIs suitable materials for developing Hall effect sensor with ultra-high sensitivity. In this work, we investigated the Hall effect sensor fabricated by Mn-doped Bi 2 Te 3 . AHE was found in Mn x Bi 2−x Te 3 material with high Mn concentration. The sensitivity of Mn x Bi 2−x Te 3 Hall effect sensor with different Mn concentration will be discussed.

The effect of variation of composition on the structural, morphological, magnetic and electric properties of Mg1−xNixCrxFe2−xO4 (x = 0.0–0.5) nanocrystallites is presented. The samples were prepared by novel polyethylene glycol (PEG) assisted microemulsion method with average crystallite size of 15–47 nm. The microstructure, chemical, and phase analyses of the samples were studied by the scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray fluorescence (ED-XRF), and X-ray diffraction (XRD). Compositional variation greatly affected the magnetic and structural properties. The high-field regimes of the magnetic loops are modelled using the Law of Approach (LOA) to saturation in order to extract information about their anisotropy and the saturation magnetization. Thermal demagnetization measurements are carried out using VSM and significant enhancement of the Curie temperature from 681 K to 832 K has been achieved by substitution of different contents of Ni–Cr. The dc-electrical resistivity (ρRT) at potential operational range around 300 K is increased from 7.5 × 108 to 4.85 × 109 Ωcm with the increase in Ni–Cr contents. Moreover, the results of the present study provide sufficient evidence to show that the electric and magnetic properties of Mg-ferrite have been improved significantly by substituting low contents of Ni–Cr.

We deposited high quality (Sb1−xBix)2Te3 on mica substrate by molecular beam epitaxy and investigated their magnetotransport properties. It is found that the average surface roughness of thin films is lower than 2 nm. Moreover, a local maxima on the sheet resistance is obtained with x = 0.043, indicating a minimization of bulk conductivity at this composition. For (Sb0.957Bi0.043)2Te3, weak antilocalization with coefficient of -0.43 is observed, confirming the existence of 2D surface states. Moreover Shubnikov-de Hass oscillation behavior occurs under high magnetic field. The 2D carrier density is then determined as 0.81 × 1016 m−2, which is lower than that of most TIs reported previously, indicating that (Sb0.957Bi0.043)2Te3 is close to ideal TI composition of which the Dirac point and Fermi surface cross within the bulk bandgap. Our results thus demonstrate the best estimated composition for ideal TI is close to (Sb0.957Bi0.043)2Te3 and will be helpful for designing TI-based devices.

Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2−xO4/BaTiO3 composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the electrostrain with doping Ga is also observed. Quantitative estimation indicates that magnetoelectric coupling is enhanced for Ga-doped CoGaxFe2−xO4/BaTiO3 composites. Thus, the present work is beneficial to the practical application of composite CoFe2O4/BaTiO3-based multiferroic materials.