427 research outputs found
Hard and semi-hard Fe-based magnetic materials
No full textIron (Fe) is the most important ferromagnetic element, not only for its high magnetic moment and high Curie temperature but for its abundance as well. Fe-based magnetic materials are therefore widely applied in technologies and industries, with most of the applications for soft magnetic materials, because of the low magnetocrystalline anisotropy (MCA) of Fe. However, it is possible to realize magnetic hardening in Fe-based materials as we have learned from the early carbon steel permanent magnets although their coercivity was modest. Recent efforts to search for rare-earth-free hard magnetic materials have shown more promising evidences for achieving high MCA in Fe-based materials. In this paper, we review the history and the recent developments of Fe-based hard and semi-hard magnetic materials with a focus on mechanisms of high MCA in Fe-based phases and the related crystal and electronic structures. We have tabulated and discussed the structures and the magnetic properties of the Fe-based binary or ternary systems containing p-block and d-block elements, with many of them showing considerable MCA. Furthermore, it is important to know and to understand that the MCA in Fe-based magnetic materials can be tailored/enhanced through chemical and/or structural modifications that will lead to “artificially engineered” hard and semi-hard magnetic materials for advanced permanent magnets in the future.This is a manuscript of an article published as Mohapatra, Jeotikanta, Xubo Liu, Pramanand Joshi, and J. Ping Liu. "Hard and semi-hard Fe-based magnetic materials." Journal of Alloys and Compounds (2023): 170258.
DOI: 10.1016/j.jallcom.2023.170258.
Copyright 2023 Elsevier B.V.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
Thermal stability of anisotropic bonded magnets prepared by additive manufacturing
No full textIn this research, anisotropic NdFeB + SmFeN hybrid and NdFeB bonded magnets are additively printed in a polyphenylene sulfide (PPS) polymer binder. Printed NdFeB + SmFeN PPS bonded magnets displayed excellent magnetic properties (Br [remanence] = 6.9 kG [0.69 T], Hcj [coercivity] = 8.3 kOe [660 kA/m], and BHmax [energy product] = 9.9 MGOe [79 kJ/m3]) with superior corrosion resistance and thermal stability. The anisotropic NdFeB bonded magnet shows a high coercivity of 14.6 kOe (1162 kA/m) with a BHmax of 8.7 MGOe (69 kJ/m3). The coercivity and remanence temperature coefficients for NdFeB + SmFeN hybrid bonded magnets are −0.10%/K and −0.46%/K, and for NdFeB bonded magnets are −0.14%/K and −0.53%/K in the range of 300–400 K, indicating that the hybrid bonded magnets are thermally stable. The average flux aging loss for hybrid magnets was also determined to be very stable over 2000 h at 448 K (175°C) in air with 2.04% compared to that of NdFeB magnets with 3.62%.This article is published as Gandha, Kinjal, Mariappan Parans Paranthaman, Haobo Wang, Xubo Liu, and Ikenna C. Nlebedim. "Thermal stability of anisotropic bonded magnets prepared by additive manufacturing." Journal of the American Ceramic Society 106, no. 1 (2023): 166-171.
DOI: 10.1111/jace.18609
Copyright 2022 The Author(s).
Attribution 4.0 International (CC BY 4.0).
Posted with permission.
DOE Contract Number(s): AC02-07CH11358; AC05-00OR22725
DCASE 2024 Task 9: Language-Queried Audio Source Separation | Development Set
No full text<p><strong>== Description == </strong></p>
<p>The development set is composed of audio samples from FSD50K [1] and Clotho v2 [2] datasets. FSD50K contains over 51k audio clips (~100 hours) manually labeled using 200 classes drawn from the AudioSet Ontology. For each audio clip in the FSD50K dataset, we generated one automatic caption for each audio clip by prompting ChatGPT (GPT-4) with its sound event tags. All audio files should be converted to mono 16 kHz audio for training LASS models. </p>
<p>Clotho v2: <a href="../records/4783391">https://zenodo.org/records/4783391</a></p>
<p>FSD50K: <a href="../records/4060432">https://zenodo.org/records/4060432</a></p>
<p>Automatic captions generated for FSD50K:</p>
<ul>
<li>fsd50k_dev_auto_caption.json</li>
<li>fsd50k_eval_auto_caption.json</li>
</ul>
<p>Prompt for generating captions:</p>
<blockquote>
<p>I will give you a number of lists containing sound events. Please write an one-sentence audio caption to describe these sounds.</p>
<p>Make sure you are using grammatical subject-verb-object sentences. Directly describe the sounds and avoid using the word “heard”. Please don't describe the temporal order of these sound events. The caption should be less than 20 words.</p>
</blockquote>
<p>In addition to the development set, participants are free to use any external data (including private data) but are not allowed to use audio in Freesound uploaded between April and October 2023. Participants must specify all external resources utilized in their submission in the technical report.</p>
<p><strong>== References ==</strong></p>
<p>[1] Fonseca E, Favory X, Pons J, et al. FSD50k: an open dataset of human-labeled sound events. IEEE/ACM Transactions on Audio, Speech, and Language Processing, 2021, 30: 829-852.</p>
<p>[2] Drossos K, Lipping S, Virtanen T. Clotho: An audio captioning dataset. IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). 2020: 736-740.</p>
<p><strong>== Contact ==</strong></p>
<p>Xubo Liu, [email protected]</p>
Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering
No full textSamarium-cobalt (Sm-Co) sintered magnets have high magnetic energy densities, great resistance to demagnetization and corrosion, and excellent thermal stability in a wide temperature range (–50–550 °C). However, the utilization of these magnets is restricted by their brittleness. Based on micromechanical and the Zener pinning model, Sm-Co sintered magnets with improved mechanical properties have been designed and fabricated via microstructure engineering. A small amount of fine Sm2O3 particulates (0–3 wt%) has been incorporated into Sm2(CoFeCuZr)17 sintered magnets to refine the grain size by up to approximately 50% (from 45 to 22 µm) and narrow the grain size distribution. Doping with 3 wt% Sm2O3 increased the flexural strength by 62% while maintaining magnetic performance. Both grain-refined unimodal microstructure and heterogeneous laminated coarse/fine grain microstructure were formed by strategically designed assemblies of Sm2O3-added Sm-Co powder feedstock mixtures. The technology is compatible with existing magnet manufacturing processes. Numerical micromechanics simulation indicates that the fracture is dominated by intragranular mode. The mechanical strength is mainly enhanced by the additive-induced grain refinement, while the small amount of Sm2O3 addition has a small direct positive contribution. These magnets will be more cost-effective, efficient, and robust for various functional applications.This is a manuscript of an article published as Cui, Baozhi, Xubo Liu, Ikenna C. Nlebedim, and Jun Cui. "Mechanically robust high magnetic-performance Sm-Co sintered magnets through microstructure engineering." Journal of Alloys and Compounds 926 (2022): 166869.
DOI: 10.1016/j.jallcom.2022.166869.
Copyright 2022 Elsevier B.V.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
Designed materials with the giant magnetocaloric effect near room temperature
No full textThe coupling between structural and magnetic degrees of freedom is crucial for realization of interesting physical phenomena associated with magneto-structural transformations resembling austenite-to-martensite transitions. Despite substantial efforts in design and discovery of materials with strong magnetocaloric effects, majority of viable candidates are composed of non-earth-abundant and toxic elements, while others involve challenging syntheses and post processing. Guided by advanced density functional theory calculation, we report a new family of compounds, i.e., Mn0.5Fe0.5NiSi1-xAlx [x = 0.045–0.07] exhibiting a giant magnetocaloric effect (MCE) that is tunable near room temperature. Their MCE functionality arises from a distinct magneto-structural transformation between a paramagnetic hexagonal Ni2In-type phase and ferromagnetic orthorhombic TiNiSi-type phase that can be actuated by magnetic field and/or pressure. As the transition is sensitive to external hydrostatic pressure, the same materials should also exhibit a strong barocaloric response in addition to the giant MCE.This is a manuscript of an article published as Biswas, Anis, Arjun K. Pathak, Nikolai A. Zarkevich, Xubo Liu, Yaroslav Mudryk, Viktor Balema, Duane D. Johnson, and Vitalij K. Pecharsky. "Designed materials with the giant magnetocaloric effect near room temperature." Acta Materialia 180 (2019): 341-348. DOI: 10.1016/j.actamat.2019.09.023. Posted with permission.</p
Engineering microstructure to improve coercivity of bulk MnBi magnet
No full textMnBi is a candidate material for high-temperature magnets because of its increasing coercivity with increasing temperatures up to 255 °C. However, most efforts in fabricating bulk MnBi magnets have run into the problem of preserving the coercivity (Hcj) of its feedstock powders. About 70% of powder's Hcj would be lost during the densification process. Our micromagnetic modeling shows that the coercivity mechanism of the MnBi bulk magnet is controlled by nucleation of the reversal magnetization domains, and the large Hcj loss that occurred during the powder consolidation process can be attributed to the inter-grain magnetic coupling. To attain a high Hcj, the grains in the MnBi bulk magnet must be separated with a non-magnetic grain boundary phase (GBP). To validate this GBP hypothesis, we engineered MnBi bulk magnets with two different types of GBP. The first type of GBP was created in-situ by precipitating excessive Bi from the grains; the second type was created ex-situ by coating silicates on the feedstock powders before the consolidation. While both GBP work, the ex-situ approach resulted in a better Hcj due to a more uniform GBP distribution. The Hcj loss was reduced from 70% to 15%, and the (BH)max of a warm sintered bulk magnet reached 8.9 MGOe.This is a manuscript of an article published as Tang, Wei, Gaoyuan Ouyang, Xubo Liu, Jing Wang, Baozhi Cui, and Jun Cui. "Engineering microstructure to improve coercivity of bulk MnBi magnet." Journal of Magnetism and Magnetic Materials 563 (2022): 169912.
DOI: 10.1016/j.jmmm.2022.169912.
Copyright 2022 Elsevier B.V.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
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Fast Latent Factor Models with Massive Correlated Data
No full textThe increasing prevalence of correlated and functional data has become a critical component of scientific discovery. Probabilistic latent factor models, renowned for their ability to model hidden patterns in full or reduced-dimensional spaces, are prevalent in modeling correlated and functional data. Furthermore, the probabilistic framework enables modeling noise and uncertainty quantification, particularly suitable for noisy observations from experiments or computer simulations. However, the computational complexity associated with factor models for modeling correlated and functional data remains a big challenge. This dissertation first introduces several fast computational approaches, including the fast Fourier transform, generalized Schur algorithm, and Kalman filter for computing the discrete Fourier transform, solving linear systems with a Toeplitz matrix of coefficients, and estimating linear dynamical systems, respectively. These algorithms reduce the computational order of solving distinct linear systems from cubic to pseudolinear order with respect to the size of the covariance matrix without approximation. Built upon these algorithms, we develop scalable approaches for latent factor models with the factors following Gaussian processes, which enable fast predictions and uncertainty quantification. We demonstrate our approaches in various applications, including estimating latent interaction functions of particle or agent-based systems, and estimating materials properties from microscopy videos. Furthermore, we implement these approaches in open-sourced software packages.
Chapter 1 reviews Gaussian processes with scalar-valued and vectorized outputs, and outlines the computational challenges of Gaussian processes. We review three computational methods that facilitate the development of new fast algorithms, including the fast Fourier transform, the generalized Schur algorithm, the Kalman filter, and Rauch-Tung-Striebel smoother. Chapter 2 introduces the marginalization technique for integrating out latent variables and presents a probabilistic framework for learning interaction laws in particle systems. We model the interaction function by Gaussian processes with exponential covariances. By reformulating the inference problem through state-space representations, we develop a new algorithm for computing the covariance matrix and vector multiplication with linear complexity without approximation. By integrating a conjugate gradient algorithm, we scalably compute the predictive distribution of particle interaction functions with massive particle trajectory data. Chapter 3 discusses latent factor representation of microscopy videos, where the factor loadings are given by the two-dimensional Fourier basis, and the covariances of the factors are Toeplitz matrices that encode physical processes. We develop a maximum marginal likelihood estimator that removes the need for selecting Fourier modes in estimation and introduces a fast approach for inversion and the log determinant of Toeplitz matrices based on the generalized Schur algorithm. We implement the tools in an open-source MATLAB package with details provided in Chapter 4. Finally, we outline future directions in Chapter 5
Site Occupancy Preference and Magnetic Properties in Nd<sub>2</sub>(Fe,Co)<sub>14</sub>B
No full textPartial replacement of Fe by Co is an effective method to increase Curie temperature (TC), which improves the thermal stability of magnetic properties in Nd2Fe14B-based permanent magnets. The correlation between Fe substitution and magnetic properties has been studied in Nd2(Fe,Co)14B via a first-principles calculation. The calculated Fe substitution energies indicate that the Co atoms avoid the 8j2 site, which agrees with the experiments. The Co atoms are ferromagnetically coupled with Fe sublattice and show magnetic moments of about 1.2 to 1.7 μB at different crystallographic sites, less than that of Fe (2.1–2.7 μB), resulting in the decrease in total magnetization at ground state (0 K) with increasing Co content. The effective exchange interaction parameter, derived from the energy difference between varied magnetic structures, increases from 7.8 meV to 17.0 meV with increasing Co content from x = 0 to x = 14 in Nd2Fe14−xCoxB. This change in the effective exchange interaction parameter is responsible for the enhancement of TC in Nd2(Fe,Co)14B. The total magnetization at 300 K, derived from mean-field theory, shows a peak maximum value at x = 1 in Nd2Fe14−xCoxB. The phenomenon results from the interplay between the reduction of the magnetic moment in the Fe(Co) sublattice and the enhancement of TC with increasing Co content
Coercivity of (Fe<sub>0.7</sub>Co<sub>0.3</sub>)<sub>2</sub>B Nanowire and Its Bonded Magnet
No full text(Fe0.7Co0.3)2B are potential permanent magnets material due to its large saturation magnetization and high Curie temperature. However, it has moderate magnetocrystalline anisotropy (MCA) and low coercivity. One way to improve its coercivity is to combine the contributions from magnetocrystalline- and magnetic-shape anisotropy by preparing (Fe0.7Co0.3)2B nanowires. We study the effects of size, morphology, and surface defects on the hard magnetic properties of nanowires using micromagnetic simulation. The hard magnetic properties of (Fe0.7Co0.3)2B nanowire-bonded magnets are estimated, including the role of inter-wire magnetostatic interaction. By considering the existence of local reductions in MCA energy of up to 30% on the surface layer of nanowires, the anisotropic bonded magnet with a 65% vol. of (Fe0.7Co0.3)2B nanowires would have typical remanence, Br= 7.6–8.4 kG, coercivity, Hci= 9.6–9.9 kOe, and maximum energy product, (BH)m = 14–17.8 MGOe. Developing effective technology for synthesizing nanowires and fabricating corresponding bonded magnets is promising for manufacturing practical magnets based on the magnetic phase with a relatively low or moderate MCA, such as (Fe0.7Co0.3)2B
Supplementary material 3 from: Liu Q, Guo Y, Yang Y, Mao J, Wang X, Liu H, Tian Y, Hao Z (2024) Geometric morphometric methods for identification of oyster species based on morphology. Biodiversity Data Journal 12: e115019. https://doi.org/10.3897/BDJ.12.e115019
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