Single-Crystal Permanent Magnets: Extraordinary Magnetic Behavior in the Ta-,Cu-, and Fe-Substituted CeCo₅ Systems

Journal Article · 24 January 2019 · Physical Review Applied

DOI: https://doi.org/10.1103/PhysRevApplied.11.014052 · OSTI ID:1494934

Lamichhane, Tej N. ^[1]; Onyszczak, Michael T. ^[2]; Palasyuk, Olena ^[1]; Sharikadze, Saba ^[2]; Kim, Tae -Hoon ^[1]; Lin, Qisheng ^[1]; Kramer, Matthew J. ^[1]; McCallum, R. W. ^[1]; Wysocki, Aleksander L. ^[1]; Nguyen, Manh Cuong ^[1]; Antropov, Vladimir P. ^[1]; Pandey, Tribhuwan ^[3]; Parker, David ^[3]; Bud’ko, Sergey L. ^[1]; Canfield, Paul C. ^[1]; Palasyuk, Andriy ^[1]

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1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
2. Iowa State Univ., Ames, IA (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

To reduce material and processing costs of commercial permanent magnets and to attempt to fill the empty niche of energy products, 10–20 MGOe, between low-flux (ferrites, alnico) and high-flux (Nd₂Fe₁₄B- and SmCo₅-type) magnets, we report the synthesis, structure, magnetic properties, and modeling of Ta-, Cu-, and Fe-substituted CeCo₅. Using a self-flux technique, we grow single crystals of Ce_15.1Ta_1.0Co_74.4Cu_9.5, Ce_16.3Ta_0.6Co_68.9Cu_14.2, Ce_15.7Ta_0.6Co_67.8Cu_15.9, Ce_16.3Ta_0.3Co_61.7Cu_21.7, and Ce_14.3Ta_1.0Co_62.0Fe_12.3Cu_10.4. X-ray-diffraction analysis shows that these materials retain a CaCu₅ substructure and incorporate small amounts of Ta in the form of “dumbbells,” filling the 2e crystallographic sites within the one-dimensional hexagonal channel with the 1a Ce site, whereas Co, Cu, and Fe are statistically distributed among the 2c and 3g crystallographic sites. Scanning-electron-microscopy, energy-dispersive-x-ray-spectroscopy, and scanning-transmission-electron-microscopy examinations provide strong evidence of the single-phase nature of the as-grown crystals, even though they readily exhibit significant magnetic coercivities of approximately 1.6 kOe to approximately 1.8 kOe caused by Co-enriched, nanosized structural defects and faults that can serve as pinning sites. Heat treatments at 1040°C for 10 h and hardening at 400°C for 4 h lead to the formation of a so-called composite crystal with a bimodal microstructure that consists of a Ta-poor matrix and Ta-rich laminal precipitates. Formation of the composite crystal during the heat treatment creates a three-dimensional array of extended defects within a primarily single-grain single crystal, which greatly improves its magnetic characteristics. Possible causes for the formation of the composite crystal may be associated with Ta atoms leaving matrix interstices at lower temperatures and/or matrix degradation induced by decreased miscibility at lower temperatures. Furthermore Fe strongly increases both the Curie temperature and magnetization of the system resulting, in (BH)_max ≈ 13 MGOe at room temperature.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1494934
• Alternate ID(s): OSTI ID: 1492120
• Report Number(s): IS-J--9882
• Journal Information: Physical Review Applied, Journal Name: Physical Review Applied Journal Issue: 1 Vol. 11; ISSN 2331-7019; ISSN PRAHB2
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English