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1. Theoretical limits for energy density of aligned ferromagnetic nanoparticles in a nonmagnetic matrix for rare-earth-free permanent magnets

   https://doi.org/10.1063/5.0233620  

   Sarker, Shouvik; Rajib, Md Mahadi; Barua, Radhika; Atulasimha, Jayasimha (March 2025, Applied Physics Letters)

   Developing permanent magnets with fewer critical elements requires understanding hysteresis effects and coercivity through visualizing magnetization reversal. Here, we numerically investigate the effect of the geometry of nanoscale ferromagnetic inclusions in a paramagnetic/nonmagnetic matrix to understand the key factors that maximize the magnetic energy product of such nanocomposite systems. Specifically, we have considered a matrix of “3 μm × 3 μm × 40 nm” dimension, which is a sufficiently large volume, two-dimensional representation considering that the ferromagnetic inclusions' thickness is less than 3.33% of the lateral dimensions simulated. Using this approach, which minimizes edge effects to approximate bulk-like magnetic behavior while remaining computationally tractable for simulation, we systematically studied the effect of the thickness of ferromagnetic strips, separation between the ferromagnetic strips due to the nonmagnetic matrix material, different saturation magnetization values, and the length of these ferromagnetic strips on magnetic coercivity and remanence by simulating the hysteresis loop plots for each geometry. Furthermore, we study the underlying micromagnetic mechanism for magnetic reversal to understand the factors that could help attain the maximum magnetic energy densities for ferromagnetic nanocomposite systems in a paramagnetic/nonmagnetic material matrix. In this study, we have used material parameters of an exemplary Alnico alloy system, a rare-earth-free, thermally stable nanocomposite, which could potentially replace high-strength NdFeB magnets in applications that do not require large energy products. However, we project the energy density (BH)max of materials with higher saturation magnetization to have an ideal theoretical limit of (BH)max ∼94 kJ/m3 (∼12 MGOe), which is ∼(35%–40%) of the energy density of Rare-Earth Free Magnets. This energy density could be higher if exchange bias from antiferromagnets, defects, and pinning is included and could stimulate further experimental work on the fabrication and large-scale manufacturing of RE-free PMs with different nanocomposite systems. 

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2. Novel Design of Six-Phase Spoke-Type Ferrite Permanent Magnet Motor for Electric Truck Application

   https://doi.org/10.3390/en15061997  

   Won, Hoyun; Hong, Yang-Ki; Choi, Minyeong; Platt, Jonathan; Bryant, Briana; Choi, Seungdeog; Li, Shuhui; Yoon, Hwan-Sik; Haskew, Timothy A.; Lee, Jongkook; et al (March 2022, Energies)

   This paper proposes a 300 kW 24-slot/10-pole 6-phase stator-shifted fractional-slot concentrated winding spoke-type ferrite permanent magnet machine for electric truck applications. The proposed motor consists of a stator with dual three-phase windings positioned 75 degrees apart to reduce higher-order MMF harmonic order, and a rotor with an inexpensive and high-resistance ferrite permanent magnet in the spoke configuration. The simulated result of the stator-shifted machine is compared with a fabricated stator-shifted machine, and the results show good agreement with each other. To further reduce the torque ripple from 2.5 to 0.9% while maintaining a high maximum torque of 2980 Nm, circular voids with a diameter of 11 mm are embedded in the rotor. The proposed motor is evaluated for irreversible demagnetization, mechanical and thermal stability, and fault tolerant ability. To assess the proposed motor performance, the electric truck simulation model is constructed using MATLAB/Simulink and used to compare with the reported 12-slot/10-pole rare-earth permanent magnet-based machine. Compared to a previously reported six-phase rare-earth permanent magnet based flat-type machine, the proposed motor can save 4.3 kWh of energy with a USD 2512 lower cost while retaining a similar motor performance. 

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3. Characterization of nanostructure ferrite material on gallium nitride on SiC substrate for millimeter wave integrated circuit

   https://doi.org/10.1063/1.4977231  

   O’Keefe, Brian; Liang, Tinghao; Afsar, Mohammad_N; Koomson, Valencia_J (February 2017, AIP Advances)

   In this paper, for the first time, the characterization of spin-casted thick Barium nano-hexaferrite film on GaN-on-SiC substrate over a broad frequency range of 30-110 GHz is presented. Real and imaginary parts of both permittivity and permeability of the ferrite/polymer film are computed from transmittance data obtained by using a free space quasi-optical millimeter wave spectrometer. The spin-casted composite film shows strong resonance in the Q band, and mixing the powder with polymer slightly shifts the resonance frequency lower compared to pure powder. The high temperature compatibility of GaN substrate enables us to run burn-out tests at temperatures up to 900°C. Significant shortening phenomenon of resonance linewidth after heat treatment was found. Linewidth is reduced from 2.8 kOe to 1.7 kOe. Experiment results show that the aforementioned film is a good candidate in applications of non-reciprocal ferrite devices like isolators, phase shifters, and circulators. 

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4. Review on mechanical, thermal, and magnetic performance of high-temperature thermoplastic bonded magnetic composites

   https://doi.org/10.1016/j.jmmm.2025.173394  

   Arigbabowo, Oluwasola K; Tate, Jitendra S; Khadka, Mandesh; Geerts, Wilhelmus J; Karkhanis, Pratik U (July 2025, Journal of magnetism and magnetic materials)

   Zheng, Hao (Ed.)

   Thermoplastic bonded magnetic composites combine the cost-effectiveness, low mass density, and manufacturing flexibility of conventional thermoplastics with the unique characteristics of magnetic powders/ fillers to form multifunctional magneto polymeric composites that offer superior properties to conventional materials. At elevated temperatures, the magnetic properties change significantly, and the polymer matrix no longer secures the magnetic particles and can rotate freely with respect to an externally applied magnetic field. This often happens at temperatures significantly below the melting point of the polymer. To extend the thermal window of bonded magnets beyond 175 ◦C (the typical temperature of rotors in motors and generators), poly- mers such as polyetheretherketone (PEEK), polyetherimide (PEI), or other high-temperature thermoplastics have been considered suitable binders for magnetic fillers. Another suggested approach is using a surface treatment to increase the adhesion between the polymer matrix and magnetic particles. In this review, the fabrication pro- cesses to make bonded magnets by injection molding and fused filament fabrication were discussed as well as their thermal, mechanical, and magnetic performance obtained via analytical and materials characterization methods. The magnetic properties of bonded permanent magnets manufactured via different techniques were discussed in terms of the most important single magnetic parameter known as “the maximum energy product- (BH)max, which can serve as a performance index for manufacturing bonded magnets. The energy product normalized on cost or mass density are used to provide insight on the performance of bonded magnets for ap- plications driven by cost or inertia. Finally, applications of high-performance thermoplastic-based magnetic composites that can be viable for stringent engineering devices such as sensors, actuators, motors, and generators were highlighted. 

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5. A Compact Electropermanent Magnet Valve Geometry for Switching of Magnetorheological Fluid Using Particle Jamming

   Gallentine, James; Kumar, Nithin S; Barth, Eric J (September 2024, In Fluid Power Systems Technology, vol. 88193, p. V001T01A024. American Society of Mechanical Engineers)

   Electropermanent magnetic (EPM) valves consist of two permanent magnets, one with high coercivity and one with relatively low coercivity, which are able to rapidly redirect the flux within a magnetic circuit. When combined with magnetorheological (MR) fluid, they provide the ability to rapidly switch flow in a hydraulic circuit on or off. EPM valves contain no moving parts and draw no power except when changing state. These facts, along with their scalability, make them an attractive option for distributed flow control in small hydraulic systems. Current examples of EPM valves are often restricted to relatively low-pressure or low-flow operation. Miniaturization of small-scale hydraulic robots, both soft and rigid, is limited by the availability of sufficiently lightweight, compact, and efficient components which are capable of directing fluid at pressures greater than 700 kPa. This research proposes an EPM valve which leverages the magnetic properties of MR fluid to channel magnetic flux through the fluid. To evaluate the proposed geometry, an exploratory prototype was constructed and evaluated using a test-bench capable of evaluating the valve as a flow resistance. Simulations were conducted to evaluate the design and validate the use of simulation for future design iteration. To be of use in robotic systems, this valve needs to be capable of rapidly switching relatively high pressures while maintaining a highly compact and easily manufactured form factor. Due to its size and low power consumption, it is suitable for distributed hydraulic control in miniature systems such as hydraulically-actuated robots, including soft robots. 

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