Structural and magnetic properties of hard magnetic system Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19)

The Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19) is a composite, hard magnetic system that is based on the CaCu5-type structure (1:5). It shows both, unique magnetic and microstructural features that are essential for permanent magnets, e.g., exceptional squareness of the 2nd. quadrant of the magnetization loops and microstructural features typically needed for pinning. Samples solidified in alumina crucibles are coarse-grained and often clearly faceted and readily align in a magnetic field. X-ray, SEM, and TEM analyses show a 1:5-type single-phase material when quenched from high temperature, which, after heat treatment, transforms into a laminar coherent nanostructure through the formation of a dense array of extended intercalated regions. These extended intercalated regions are comprised of segments of the Ce2Ni7–type structure (2:7) which segregate into various closely related precipitates forming a nanostructure similar to the SmCo5 - Sm2Co17 composites seen in Sm-Co permanent magnets. Based on TEM and Lorentz microscopy of well-aligned single grain particles, the magnetic domains’ reversal mechanism is regulated by anisotropy fluctuations occurring along the easy direction of magnetization and strong exchange interactions between the matrix and defects (e.g.: stacking faults). Lorentz microscopy suggests the domain wall is not physically pinned by the defect, but rather is offset/deflected when it interacts with the defect. The Lorentz and magnetization data suggest that defects cause a bending of the moment away from the c axis inside the grains.</p

Electrochemistry of Praseodymium in Aqueous Solution Using a Liquid Gallium Cathode

The electrochemistry of liquid Ga electrodes in aqueous media was examined in the presence of praseodymium acetate (PrOAc) as an alternate path for low temperature reduction of rare earth elements (REE). This study investigated the aqueous electrochemistry of Ga with and without REEs (Pr). Cyclic voltammetry experiments showed that in the presence of PrOAc, an order of magnitude increase in cathodic current was observed for the Ga electrode, compared to that in the absence of Pr. Decrease in the reduction current with the increase of scan rate, with and without Pr, suggests catalytic reactions following electron transfer, which was attributed to the Ga2O disproportionation reaction. Chronoamperometric experiments performed in Pr containing solutions formed a precipitate. Over 50% of the Pr ions from the aqueous electrolyte were immobilized in the precipitate; a solid Ga-rich phase. Formation of this precipitate was only possible when Ga oxidation was induced. This condition was achieved by circulation of liquid Ga from the pool via external pump and returned dropwise to the liquid Ga pool. When the collected precipitate was leached in dilute HCl, Pr was released with H2 evolved as a byproduct, and Ga returned to its initial liquid metallic state. These preliminary results show encouraging new routes that could be applied for the recovery of diluted REE leachates, such as those obtained from magnets, coal fly ash, and ores.This is a manuscript of an article published as Engmann, Eugene, Luis A. Diaz, Tedd E. Lister, Olena Palasyuk, and Haiyan Zhao. "Electrochemistry of Praseodymium in Aqueous Solution Using a Liquid Gallium Cathode." Journal of The Electrochemical Society 169, no. 6 (2022): 063519. DOI: 10.1149/1945-7111/ac76e3. Copyright 2022 IOP Publishing Ltd. Posted with permission. DOE Contract Number(s): AC02-07CH11358, AC07-05ID14517; AC07-05ID14517; AC02-07CH11358

Construction of A-B heterolayer intermetallic crystals: Case studies of the 1144-phase TM-phosphides AB(TM)(4)P-4 (TM=Fe, Ru, Co, Ni)

The discovery of the 1144 phase, e.g., CaKFe4As4, creates opportunities to build novel intermetallics with alternative stacking of two parent compounds. Here we formalize the idea by defining a class of bulk crystalline solids with A-B stacking (including 1144 phases and beyond), which is a generalization of heterostructures from few-layer or thin-film semiconductors to bulk intermetallics. Theoretically, four families of phosphides AB(TM)(4)P-4 (TM=Fe, Ru, Co, Ni) are investigated by first-principles calculations, wherein configurational, vibrational, and electronic degrees of freedom are considered. It predicts a variety of stable 1144 phases (especially Ru- and Fe-phosphides). Stability rules are found and structural/electronic properties are discussed. Experimentally, we synthesize high-purity CaKRu4P4 as a proof of principle example. The synthetic method is simple and easily applied. Moreover, it alludes to a strategy to explore complex multicomponent compounds, facilitated by a phase diagram coordinated by collective descriptors.This article is published as Song, B. Q., Mingyu Xu, Vladislav Borisov, Olena Palasyuk, C. Z. Wang, Roser Valentí, Paul C. Canfield, and K. M. Ho. "Construction of A− B heterolayer intermetallic crystals: Case studies of the 1144-phase TM-phosphides AB (TM) 4 P 4 (TM= Fe, Ru, Co, Ni)." Physical Review Materials 5, no. 9 (2021): 094802. DOI: 10.1103/PhysRevMaterials.5.094802. Copyright 2021 American Physical Society Posted with permission. DOE Contract Number(s): [not available

Effects of High Magnetic Fields on Phase Transformations in Amorphous Nd2Fe14B

We briefly summarize the results from a set of experiments designed to demonstrate the effects of high magnetic fields applied during thermal annealing of amorphous Nd2Fe14B produced through melt-spinning. A custom-built differential scanning calorimeter was used to determine the crystallization temperatures in zero-field and in applied fields of 20 kOe and 90 kOe, which guided subsequent heat treatments to evaluate phase evolution. X-ray diffraction was used for phase identification and transmission electron microscopy was employed for observation of the crystallite size and morphology. Magnetization measurements were also used to evaluate the resulting magnetic phases after thermomagnetic processing. While the applied magnetic fields do not appear to affect the crystallization temperature, significant effects on the kinetics of phase evolution are observed and correlated strongly to the magnetic behavior.</p