High-temperature Magnetic Material Research Articles

RETRACTED ARTICLE: Study on the structure and magnetic properties of Gd-doped LTPMnBi

Series samples MnBi1-xGdx (x = 0, 0.04, 0.08, 0.12, and 0.16) were prepared and studied the structure and magnetic properties. The Rietveld refinement results showed that the low-temperature phase MnBi content in these samples is above 78% and the doped atoms occupied the position of Bi in the MnBi crystal structure. The Debye temperature is founding to decrease with increasing doping. The Curie temperature, paramagnetic to ferromagnetic transition temperature, thermal hysteresis, saturation magnetization, and coercive force of the samples change significantly with increasing doping content. Within a temperature range of 300–500 K, a positive coercivity temperature coefficient β existed. This work helps MnBi-Gd as a candidate for high-temperature magnetic material applications and contributes to the development of tailoring magnetic properties.

Thiosemiquinoid Radical-Bridged CrIII2 Complexes with Strong Magnetic Exchange Coupling.

Semiquinoid radical bridging ligands are capable of mediating exceptionally strong magnetic coupling between spin centers, a requirement for the design of high-temperature magnetic materials. We demonstrate the ability of sulfur donors to provide much stronger coupling relative to their oxygen congeners in a series of dinuclear complexes. Employing a series of chalcogen donor-based bis(bidentate) benzoquinoid bridging ligands, the series of complexes [(TPyA)2Cr2(RL4-)]2+ (OLH4 = 1,2,4,5-tetrahydroxybenzene, OSLH4 = 1,2-dithio-4,5-dihydroxybenzene, SLH4 = 1,2,4,5-tetrathiobenzene, TPyA = tris(2-pyridylmethyl)amine) was synthesized. Variable-temperature dc magnetic susceptibility data reveal the presence of weak antiferromagnetic superexchange coupling between CrIII centers in these complexes, with exchange constants of J = -2.83(3) (OL4-), -2.28(5) (OSL4-), and -1.80(2) (SL4-) cm-1. Guided by cyclic voltammetry and spectroelectrochemical measurements, chemical one-electron oxidation of these complexes gives the radical-bridged species [(TPyA)2Cr2(RL3-•)]3+. Variable-temperature dc susceptibility measurements in these complexes reveal the presence of strong antiferromagnetic metal-semiquinoid radical coupling, with exchange constants of J = -352(10) (OL3-•), - 401(8) (OSL3-•), and -487(8) (SL3-•) cm-1. These results provide the first measurement of magnetic coupling between metal ions and a thiosemiquinoid radical, and they demonstrate the value of moving from O to S donors in radical-bridged metal ions in the design of magnetic molecules and materials.

Crystal structures and magnetic performance of nanocrystalline Sm-Co compounds

A variety of intermetallic compounds in the binary Sm-Co system were reviewed, and the contents were focused on the crystal structures, magnetic properties and the nanoscale effects. The representative nanocrystalline Sm-Co compounds were introduced in details, the diagrams for their lattice structures and the atomic sites and occupancies were provided. Moreover, the magnetic properties of the nanocrystalline Sm-Co compounds were compared with those of the conventional polycrystalline counterparts. It showed that the nanocrystalline Sm-Co compounds exhibit special phase stability and remarkably enhanced magnetic performance, which are promising candidates for the matrix phases to develop permanent magnets, particularly the advanced high-temperature magnetic materials.

Effect of surface modification on mechanical properties and thermal stability of Sm–Co high temperature magnetic materials

The effects of different surface modifications on the mechanical properties and thermal stability of Sm–Co high temperature magnets are reported in this paper. The fracture toughness was increased by 76% for the specimens modified with the Ni plating from sulfamate electrolyte. Compared to the uncoated magnets, the thermal stability of the modified magnets was improved by 143% in high vacuum condition for aging at 500 °C up to 3000 h and by 761% in air for aging at 500 °C up to 2700 h. Microstructures of the specimens with and without surface modifications were studied using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), showing different fracture patterns. The improvements in mechanical properties were made by closing the infinite crack-origin sites on the surface of the magnets with ductile metal. The striking improvement in thermal stability was achieved by sealing the magnet body with corrosion resistive metal to limit oxidation. The adhesive bond strength between the magnet and the modified surface plays an important role in these improvements. The nickel plating from sulfamate electrolyte provides epitaxial growth of Ni from the surface of the Sm–Co magnet, which results in a stronger bond strength in between the Ni and the base material than that of the Sm–Co base material itself. Improved mechanical properties and thermal stability will benefit the development of compact, high power density electric propulsion devices for NASA's space missions.

Formation and magnetic properties of Co–Fe-based bulk metallic glasses with supercooled liquid region

A new Co–Fe-based ferromagnetic bulk metallic glass (BMG) was synthesized by copper mould casting method. The thermal stability and crystallization processes were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The soft magnetic behavior was studied by DC magnetic measurements. The high glass formation ability was interpreted in terms of the effective suppression of nucleation and growth of the intermetallic compounds which appear in the multicomponent system during solidification. The high thermal stability indicates that the new Co–Fe-based BMG could be used as high-temperature magnetic material. The low coercivity which was as low as 8 A/m for the as-cast sample was found in the Co–Fe-based metallic glass cylinder with a diameter of 1.5 mm.

Application of high temperature magnetic materials

The trend in both military and commercial markets for greater affordability has prompted the electromechanical designer toward higher speed and higher operating temperature devices. New magnetic materials are essential for the success of many of these power generation, distribution, and utilization systems. This manuscript briefly describes some of the applications for advanced high temperature magnets.