Micromagnetics of rare-earth efficient permanent magnets

Fischbacher, Johann; Kovacs, Alexander; Gusenbauer, Markus; Oezelt, Harald; Exl, Lukas; Bance, Simon; Schrefl, T.

doi:10.1088/1361-6463/aab7d1

Cited by 95 publications

(59 citation statements)

References 171 publications

(277 reference statements)

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“…Magnetic anisotropy constants and FA as a function of temperature for the system of 10 × 10 × 7 unit cells. Inset show FA(T ) for each system size, (Lx, Ly, Lz) = (6, 6, 4),(8,8,6),(10,10,7), and the extrapolation data (Lx ∝ N 1/3 → ∞).…”

mentioning

confidence: 99%

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

Toga¹,

Nishino²,

Miyashita³

et al. 2018

Phys. Rev. B

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We examine the anisotropic properties of the exchange stiffness constant, A, for rare-earth permanent magnet, Nd2Fe14B, by connecting analyses with two different scales of length, i.e., Monte Carlo (MC) method with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a continuous magnetic model. The atomistic MC simulations are performed on the spin model of Nd2Fe14B constructed from ab-initio calculations, and the LLG micromagnetics simulations are performed with the parameters obtained by the MC simulations. We clarify that the amplitude and the thermal property of A depend on the orientation in the crystal, which are attributed to the layered structure of Nd atoms and weak exchange couplings between Nd and Fe atoms. We also confirm that the anisotropy of A significantly affects the threshold field for the magnetization reversal (coercivity) given by the depinning process.

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mentioning

confidence: 99%

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

Toga¹,

Nishino²,

Miyashita³

et al. 2018

Phys. Rev. B

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“…Permanent micromagnets are a sintered mix of rareearth element powders and are typically coated for protection or passivation 29 . The micromagnets in this work are cubes and magnetized to N52 grade (SM Magnetics Co.).…”

Section: Permanent Micromagnetsmentioning

confidence: 99%

“…At the same time, market demand from the hard disk drive industry and others has pushed the development of rare-earth permanent magnets. High anisotropy, small size, high remanence, and a large variety of coatings for automotive, medical, and consumer products have led to diverse commercial availability 29 . At first glance, the benefits of combining these technologies into a sensor are low power consumption, a small size, and low cost.…”

Section: Introductionmentioning

confidence: 99%

100 pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer

et al. 2020

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Magnetic sensing is present in our everyday interactions with consumer electronics and demonstrates the potential for the measurement of extremely weak biomagnetic fields, such as those of the heart and brain. In this work, we leverage the many benefits of microelectromechanical system (MEMS) devices to fabricate a small, low-power, and inexpensive sensor whose resolution is in the range of biomagnetic fields. At present, biomagnetic fields are measured only by expensive mechanisms such as optical pumping and superconducting quantum interference devices (SQUIDs), suggesting a large opportunity for MEMS technology in this work. The prototype fabrication is achieved by assembling micro-objects, including a permanent micromagnet, onto a postrelease commercial MEMS accelerometer using a pick-and-place technique. With this system, we demonstrate a room-temperature MEMS magnetic gradiometer. In air, the sensor's response is linear, with a resolution of 1.1 nT cm −1 , spans over 3 decades of dynamic range to 4.6 µT cm −1 , and is capable of off-resonance measurements at low frequencies. In a 1 mTorr vacuum with 20 dB magnetic shielding, the sensor achieves a 100 pT cm −1 resolution at resonance. This resolution represents a 30-fold improvement compared with that of MEMS magnetometer technology and a 1000-fold improvement compared with that of MEMS gradiometer technology. The sensor is capable of a small spatial resolution with a magnetic sensing element of 0.25 mm along its sensitive axis, a >4-fold improvement compared with that of MEMS gradiometer technology. The calculated noise floor of this platform is 110 fT cm −1 Hz −1/2 , and thus, these devices hold promise for both magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

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“…Micromagnetic simulations can be a vital tool to improve the understanding of permanent magnets and their macroscopic properties. Widely used measures to determine the quality of permanent magnets are the nucleation field H n , the coercive field H c and the energy density product BH max 9 . Here we denote the critical value of the external field at which the magnetization starts to switch irreversibly as nucleation field H n 10 .…”

Section: Introductionmentioning

confidence: 99%

Extracting local nucleation fields in permanent magnets using machine learning

et al. 2020

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Microstructural features play an important role in the quality of permanent magnets. The coercivity is greatly influenced by crystallographic defects, like twin boundaries, as is well known for MnAl-C. It would be very useful to be able to predict the macroscopic coercivity from microstructure imaging. Although this is not possible now, in the present work we examine a related question, namely the prediction of simulated nucleation fields of a quasi-three-dimensional (rescaled and extruded) system constructed from a two-dimensional image. We extract features of the image and analyze them via machine learning. A large number of extruded systems are constructed from 10 × 10 pixel sub-images of an Electron Backscatter Diffraction (EBSD) image using an automated meshing procedure. A local nucleation field is calculated by micromagnetic simulation of each quasi-three-dimensional system. Decision trees, trained with the simulation results, can predict nucleation fields of these quasi-three-dimensional systems from new images within seconds. As for now we cannot quantitatively predict the macroscopic coercivity, nevertheless we can identify weak spots in the magnet and see trends in the nucleation field distribution.

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Micromagnetics of rare-earth efficient permanent magnets

Cited by 95 publications

References 171 publications

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnet Nd2Fe14B

100 pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer

Extracting local nucleation fields in permanent magnets using machine learning

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