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This work reports the first demonstration of in situ magnetic-field-assisted Directed Energy Deposition (DED) for fabricating phase-separated Alnico permanent magnets. A custom Halbach array of N52 NdFeB magnets generated an in-plane magnetic flux density of ∼1250 G during deposition, influencing melt-pool convection and solidification. Using optimized DED parameters (1000 W laser power, 450 mm/s scan speed, 300 μm layer thickness), both cuboid and ring-shaped geometries were produced. Field-assisted cuboids exhibited distinct dogbone morphologies attributed to magnetohydrodynamic flow, while ring geometries showed enhanced dimensional uniformity and improved phase homogeneity. X-ray diffraction confirmed suppression of spinodal decomposition in the as-processed state and formation of α1 (Fe–Co–rich) and α2 (Ni–Al–rich) phases after heat treatment. Magnetometry revealed improved coercivity and magnetic anisotropy in field-assisted samples, achieving an energy product of (BH)max = 0.53 MGOe. These findings establish magnetic-field-assisted DED as a scalable pathway for engineering the microstructure of nanocomposite magnetic materials.
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The EB Correlation in Resolved Polarized Images: Connections to the Astrophysics of Black Holes
Abstract We present an in-depth analysis of the newly proposed correlation function in visibility space, between the E and B modes of linear polarization, hereafter the EB correlation, for a set of time-averaged general relativistic magnetohydrodynamical simulations compared with the phase map from different semianalytic models and the Event Horizon Telescope (EHT) 2017 data for M87*. We demonstrate that the phase map of time-averaged EB correlation contains novel information that might be linked to black hole (BH) spin, accretion state, and electron temperature. A detailed comparison with a semianalytic approach with different azimuthal expansion modes shows that to recover the morphology of real/imaginary part of the correlation function and its phase, we require higher orders of azimuthal modes. To extract the phase features, we use Zernike polynomial reconstruction developing an empirical metric to break degeneracies between models with different BH spins that are qualitatively similar. We use a set of geometrical ring models with various magnetic and velocity field morphologies, showing that both the image space and visibility-based EB -correlation morphologies in magnetically arrested disk simulations can be explained with simple fluid and magnetic field geometries as used in ring models. Standard and normal evolutions by contrast are harder to model, demonstrating that the simple fluid and magnetic field geometries of ring models are not sufficient to describe them owing to higher Faraday rotation depths. A qualitative comparison with the EHT data demonstrates that some of the features in the phase of EB correlation might be well explained by the current models for BH spins and electron temperatures, while others require larger theoretical surveys.
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- PAR ID:
- 10465892
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 955
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/acdc96
