Advanced Magnetic Materials for Energy and Power Conversion Applications: Advances in Characterization, Processing, and Design of Magnetic Materials
Sponsored by: TMS Functional Materials Division, TMS: Magnetic Materials Committee
Program Organizers: Richard Beddingfield, GE; Daniel Salazar, BCMaterials; Alex Leary, NASA Glenn Research Center; Huseyin Ucar, California Polytechnic University,Pomona; Yongmei Jin, Michigan Technological University; Arcady Zhukov, University of the Basque Country
Thursday 2:00 PM
March 18, 2021
Room: RM 25
Location: TMS2021 Virtual
Session Chair: Daniel Salazar, BCMaterials
2:00 PM Invited
Magnetic Domain Tomography: Rudolf Schaefer1; 1Ifw Dresden
The magnetic domains in bulk, non-transparent magnetic specimens are not accessible by simply cleaving the sample as the domains would immediately adapt to the new surface. Therefore, in the past, domain analysis on bulk materials was usually performed by surface domain observation and by using arguments from domain theory to infer the inner domains. In recent years, however, there was impressive progress in the development of magnetic tomographic imaging, which has the potential to disclose the complete domain structure. In this presentation those novel methods, which comprise full-field soft x-ray spectromicroscopy, hard x-ray tomography, off-axis electron holography, and neutron dark-field microscopy, are reviewed. Emphasise will be on Libovicky tomography [1], which is applied to reveal the true three-dimensional structure of characteristic domain patterns in ironlike material. [1] R. Schäfer and S. Schinnerling: Tomography of basic magnetic domain patterns in ironlike bulk material. Phys. Rev. B 101, 214430 (2020)
2:30 PM
A Refinement Program to Characterize Single Crystal Magnetic Diffuse Scattering from Neutron Diffraction Experiments: Zachary Morgan1; Feng Ye2; 1Michigan Technological University; 2Oak Ridge National Laboratory
A model-free program for analyzing the diffuse scattering of single crystals due to magnetic disorder is showcased. The recently developed program for users of single crystal diffraction instruments at Oak Ridge National Laboratory is capable of extracting real-space magnetic moment correlations from neutron diffraction experiments. In particular, the high quality instruments provide a wide range of sample environments that enable the study of short range ordering in magnetic materials under high and low temperatures, pressures, and magnetic fields. An example of a refinement is shown with iron manganese oxide mineral bixbyite which is a geometrically frustrated antiferromagnetic crystal. The optimized program is fast and user-friendly allowing users to efficiently characterize the underlying disordered structures of magnetic crystals ultimately aiding in the development of emerging and advanced magnetic materials.
2:50 PM
Scale-up Production on MnBi Magnet with High Performance: Wei Tang1; Gaoyuan Ouyang1; Xubo Liu1; Baozhi Cui1; Kevin Dennis1; Jun Cui2; 1Ames Laboratories; 2Iowa State University
This work presents a new roadmap towards the large-scale fabrication of MnBi magnets. Feedstock powder was fabricated by melt-spun ribbons through prolonged annealing and low energy ball milling processes. The feedstock powders obtained Hcj of 12.3 kOe and maximum energy product, (BH)max, of 13.2 MGOe. Bulk magnets were made through magnetic alignment, pre-pressing, cold isostatic pressing, and warm-sintering. Our study revealed that a non-ferromagnetic second phase must be present at the grain boundary to retain the high Hcj in the bulk magnet. The second phase was introduced by either in-situ or ex-situ method. Additionally, the warm-sintering with a magnetic field further improved the magnetic properties of bulk magnets. A bulk magnet with Hcj of 6.4 and 18.7 kOe, and (BH)max of 8.9 and 7.5 MGOe at 25 and 150ºC, respectively, was obtained. The newly developed technical routes could commercially produce high purity powder and bulk magnets with high magnetic performance.
3:10 PM Invited
Exchange-coupled Ferromagnetism in Self-assembled Co-Pt Nanochessboards: Jerrold Floro1; 1University of Virginia
Eutectoid decomposition of bulk Co-Pt alloys in the A1 phase, with composition near 60% Pt, can result in formation of the unique nanochessboard structure. The nanochessboard is a self-assembled, 2+1D-periodic stacking of magnetically hard L10 nanorods embedded in a soft L12 matrix, all separated by coherent interfaces. Lateral lengthscales of the chessboard range from 20-40 nm. As such, the chessboard is a fascinating structure in which to examine exchange coupling, since it exhibits intermediate complexity between epitaxial bilayers and nanocrystalline aggregates. This talk will show how ferromagnetic exchange-coupling depends on lengthscale, quantify the role of hierarchical structure on the coercivity, and discuss insights into the exchange coupling and magnetization reversal mechanisms obtained from micromagnetics simulations. Recent attempts to synthesize nanochessboards in the advantageous Fe-Pt system will also be discussed. Support of the National Science Foundation through grants DMR-1105336 and DMR-1709914 is gratefully acknowledged.
3:40 PM Invited
Neutron Diffraction: A Key Tool to Unravel the Magnetic Behaviour in Heusler Alloys: Jose Maria Porro1; 1BCMaterials & Ikerbasque
Neutron diffraction is a powerful tool that allows to depict not only the atomic site occupancies in magnetic metal alloys, but also the magnetic site densities in each atomic position within the lattice. In this talk a combination of powder neutron diffraction, in polycrystalline samples, and non-polarized/polarized single crystal neutron diffraction measurements, in single crystals, will be discussed for a series of ferromagnetic Heusler alloys. More concretely, a series of six-element NiMnGaCoCuFe ferromagnetic shape memory alloys is studied using the aforementioned techniques. Based on the atomic site occupancies and additional measurements of the saturation magnetization, the influence of the structure and atomic ordering on the magnetism in these materials is analysed. The most promising candidate to present magnetic actuation at high temperatures was grown as single crystal and studied by single crystal neutron diffraction, obtaining a full map of the spin densities in the unit cell of the crystal.
4:10 PM
Magnetic Field-assisted HDDR Processing of NdFeB Powders: Michael Kesler1; Xubo Lui2; Ikenna Nlebedim2; Matthew Kramer2; Michael McGuire1; 1Oak Ridge National Laboratory; 2Ames Laboratory
The production of bonded magnets is the largest domestic permanent magnet industry and there is a need for a domestic supply of high-performance powders for their applications. Hydrogenation-disproportionation-desorption-recombination (HDDR) is an effective process for producing iso- and anisotropic powders for bonded magnet applications. Enhancing the powder performance would reduce the volume of costly rare earths needed for a given application. Applying magnetic fields to gaseous reactions provides the potential to improve these processes via the Zeeman affect, resulting in higher reactivity of the gaseous environment. Here we report the design and construction of a custom built HDDR reaction vessel for use in a 12.7 cm bore 9 Tesla superconducting magnet. We summarize results of our studies of the effects of high magnetic field applied during HDDR processing on the microstructure and magnetic properties of NdFeB-based alloys.
4:30 PM
Magnetic Domain Observation by Soft X-ray Magnetic Circular Dichroism Microscopy of Nd-Fe-B-Ga Sintered Magnets Under High Magnetic Field and High Temperature: Andres Martin Cid1; Shintaro Kobayashi2; David Billington2; Kentaro Toyoki2; Yoshinori Kotani2; Yukio Takada3; Takashi Sato3; Yuji Kaneko3; Akira Kato4; Taisuke Sasaki5; Tadakatsu Ohkubo5; Kazuhiro Hono5; Satoshi Hirosawa5; Motohiro Suzuki2; Tetsuya Nakamura6; 1Japan Synchrotron Radiation Research Institute (JASRI), SPring-8; 2Japan Synchrotron Radiation Research Institute (JASRI), SPring-8; 3Toyota Central R&D Labs, Inc; 4Advanced Material Engineering Division, Toyota Motor Corporation; 5National Institute for Materials Science; 6Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University
The addition of Ga to Nd-Fe-B sintered magnets has been reported to induce much larger coercivity enhancements than standard Nd-Fe-B sintered magnets after a post-sintered annealing process. This enhancement is connected to an improved grain boundary with a reduced amount of Fe and the presence of the antiferromagnetic Nd6(Fe,Ga)14 phase, although the role of this phase has not been yet clarified. In this work, we show the observation by soft X-ray magnetic circular dichroism microscopy of the magnetic domain reversal process of a Nd-Fe-B-Ga sintered magnet at several temperatures below and above the Néel temperature (TN) of the Nd6(Fe,Ga)14 phase (~130 °C) up to 200 °C. We found that some grains exhibit a change from single-domain to multi-domain reversal when increasing the temperature above the TN. This experimental result is possibly the beginning to clarify the relationship between the coercivity and the magnetism of the Nd6(Fe,Ga)14 phase.