Free Permanent Magnets Research Articles

Role of Disordered Precursor in L10 Phase Formation in FePt-Based Nanocomposite Magnet

In order to prove the usefulness of having a structurally disordered precursor to the formation of FePt L10 phase and to facilitate the co-existence of exchange coupled hard and soft magnetic phases with optimized magnetic properties in various conditions of annealing, a Fe-Pt-Zr-B melt spun alloy has been synthesized and detailed structural and magnetic investigations have been undertaken to probe its phase evolution during annealing. The dynamics of formation of the hard magnetic L10 phase during the gradual disorder–order phase transformation has been monitored by using a complex combination of X-ray diffraction methods and 57Fe Mössbauer spectroscopy methods, over a wide range of annealing temperatures. Multiple phases co-existing in the annealed sample microstructures, observed in XRD, have been reconfirmed by the Mössbauer spectra analysis and, moreover, accurate quantitative data have been acquired in what concerns the relative abundance of each of the observed crystalline phases in every stage of annealing. It is shown that the formation of the hard magnetic phase, emerging from the chemically disordered precursor, is gradual and occurs via complex mechanisms, involving the presence of a disordered Fe-Zr-B-rich intergranular region which contributes to an increase in the abundance of the L10 phase for higher annealing temperatures. Magnetic measurements have confirmed the good performances of these alloys in terms of coercivity and remanence. These results contribute to the development of these alloys as the next generation of rare earth, free permanent magnets.

Challenges toward development of rear‐earth free FeCo based permanent magnet

AbstractAmong the various permanent magnets reported to date, FeNdB exhibits the highest magnetic performance, but reducing the use of the rare‐earth elements is necessary to avoid exhaustion of rare‐earth elements. The key to improve the performance of permanent magnets is to increase magnetization and coercivity. FeCo has a very large magnetization, but has a very small coercivity caused by the extremely small magnetic anisotropy due to the cubic crystal structure, so that FeCo has long been unsuitable for permanent magnets. However, recent reports have revealed that the transformation of the crystal structure from cubic to tetragonal causes large magnetic anisotropy. In 2017, the author reported that a large coercivity can be obtained by fabricating tetragonal FeCo nanodots. This article reviews recent progress of rear‐earth free permanent magnets especially for the tetragonal FeCo based alloys.

Enhancement of Hard Magnetic Properties in Fraktal-Like Nano and Mesoscopic Grains.

The paper refers to Monte Carlo magnetic simulations for fractal-like nano and mesoscopic grains. The analyzed objects differed in the size, surface development, magnetic anisotropy and the spin values attributed to the system nodes inside the fractal. Such an approach allowed us to determine their magnetization processes as well as optimization characteristics in the direction to enhancement of hard magnetic properties. As it was shown, the size effects depend on the chosen value of magnetic anisotropy. In the case of fractals with ultra-high coercivity, the decreasing of their size leads to deterioration of coercivity, especially for the high surface to volume ratio. Opposite effects were observed for soft magnetic fractals when the nanostructure caused an appearance of the coercive field, and the maximum of energy product was predictably significantly higher than for conventional rare earths’ free permanent magnets.

Applying high‐throughput computational techniques for discovering next‐generation of permanent magnets

AbstractThe uncertainty in rare‐earth market resulted in worldwide efforts to develop rare‐earth‐lean/free permanent magnets. In this paper, we discuss about this problem and analyse how advances in computational and theoretical condensed matter physics could be essential in the development of a new generation of high‐performance permanent magnets via high‐throughput computational technique for material design. Additionally, we show that an adaptive genetic algorithm based methodology could be a useful tool for finding new magnetic phases. In particular, we apply such approach to Fe0.75Sn0.25 compound recovering well‐known experimental results and also finding new low‐energy magnetic metastable structures. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Temperature/Pressure on Lattice Dynamics of FeNi

Tetratenite phase of L10 (CuAu) FeNi is identified as a hard ferromagnet in spite of that common FeNi alloys are classified as a soft magnet. Due to its strong magnetic anisotropy and large coercivity, tetrataenite phase of L10 FeNi is under investigation as a rare earth free advanced permanent magnet. Our computed equilibrium lattice constant and c/a ratio for tetratenite phase of L10 (CuAu) FeNi are in 10 % deviation with the other available results. The vibrational and electronic properties of L10 FeNi at finite temperatures/pressures are studied using the first-principles plane wave self-consistent method under the framework of density functional theory. Conclusions based on the phonon dispersion curves, phonon density of states and electronic band structure along with total and projected density of states at finite temperatures/pressures are outlined.

TỔ CHỨC DẠY HỌC THEO GÓC BÀI “SỰ RƠI TỰ DO”, CHƯƠNG TRÌNH VẬT LÍ TRUNG HỌC PHỔ THÔNG VÀ BÀI “NAM CHÂM VĨNH CỬU”, CHƯƠNG TRÌNH VẬT LÍ TRUNG HỌC CƠ SỞ THEO ĐỊNH HƯỚNG PHÁT TRIỂN NĂNG LỰC HỌC SINH

TỔ CHỨC DẠY HỌC THEO GÓC BÀI “SỰ RƠI TỰ DO”, CHƯƠNG TRÌNH VẬT LÍ TRUNG HỌC PHỔ THÔNG VÀ BÀI “NAM CHÂM VĨNH CỬU”, CHƯƠNG TRÌNH VẬT LÍ TRUNG HỌC CƠ SỞ THEO ĐỊNH HƯỚNG PHÁT TRIỂN NĂNG LỰC HỌC SINH