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Title: Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets

Abstract

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.

Authors:
; ; ;  [1]; ; ;  [2]
  1. Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)
  2. All-Russia Institute of Aviation Materials (Russian Federation)
Publication Date:
OSTI Identifier:
22617206
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 123; Journal Issue: 2; Other Information: Copyright (c) 2016 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALLOYS; BORON COMPOUNDS; COBALT COMPOUNDS; DYSPROSIUM COMPOUNDS; IRON COMPOUNDS; MAGNETIZATION; NEODYMIUM COMPOUNDS; NOISE; PERMANENT MAGNETS; RARE EARTH COMPOUNDS; SAMARIUM COMPOUNDS; TERNARY ALLOY SYSTEMS; TRANSITION ELEMENT COMPOUNDS; VISCOSITY

Citation Formats

Dmitriev, A. I., E-mail: aid@icp.ac.ru, Talantsev, A. D., E-mail: artgtx32@mail.ru, Kunitsyna, E. I., Morgunov, R. B., Piskorskii, V. P., Ospennikova, O. G., and Kablov, E. N. Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets. United States: N. p., 2016. Web. doi:10.1134/S106377611606011X.
Dmitriev, A. I., E-mail: aid@icp.ac.ru, Talantsev, A. D., E-mail: artgtx32@mail.ru, Kunitsyna, E. I., Morgunov, R. B., Piskorskii, V. P., Ospennikova, O. G., & Kablov, E. N. Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets. United States. doi:10.1134/S106377611606011X.
Dmitriev, A. I., E-mail: aid@icp.ac.ru, Talantsev, A. D., E-mail: artgtx32@mail.ru, Kunitsyna, E. I., Morgunov, R. B., Piskorskii, V. P., Ospennikova, O. G., and Kablov, E. N. 2016. "Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets". United States. doi:10.1134/S106377611606011X.
@article{osti_22617206,
title = {Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets},
author = {Dmitriev, A. I., E-mail: aid@icp.ac.ru and Talantsev, A. D., E-mail: artgtx32@mail.ru and Kunitsyna, E. I. and Morgunov, R. B. and Piskorskii, V. P. and Ospennikova, O. G. and Kablov, E. N.},
abstractNote = {The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.},
doi = {10.1134/S106377611606011X},
journal = {Journal of Experimental and Theoretical Physics},
number = 2,
volume = 123,
place = {United States},
year = 2016,
month = 8
}
  • Major and minor hysteresis loop measurements have been performed on Nd{sub 15.1}Fe{sub 76.9}B{sub 8} sintered magnet. The coercivity as a function of the maximum magnetizing field has been determined. This dependence appeared to be typical of nucleation hardened materials. The domain structure behavior during the magnetization reversal has been observed on the surface parallel to the alignment direction of the sample. Domain structure photographs have been correlated with suitable points on both virgin and demagnetization curves, respectively. It was stated from this observation that the demagnetization process occurs by the nucleation of reversed domains at the grain boundaries.
  • Results of experiments to study the effect of grain size and grain-size distribution on the intrinsic coercivity and the hysteresis loop of sintered Fe-Nd-B magnets are presented. It is shown that the intrinsic coercivity decreases as the average grain size of the magnet is increased. It is also shown that the intrinsic coercivity decreases linearly with the logarithm of the square of the grain size. This is consistent with the predictions made based upon the statistical model developed in Part I. An increase in the sintering temperature leads to an increase in the average grain size, which consequently leads tomore » a narrower hysteresis loop and lower intrinsic coercivity compared to magnets sintered at a lower temperature. It is also shown that a heterogeneous grain-size distribution, such as a bimodal distribution, causes kinks to appear in the second quadrant of the hysteresis loop. By examining magnets with different fractions of large grains, the prediction that the magnitude of the kinks increases with the volume fraction of the large grains, has been verified experimentally.« less
  • In discussing a previous statistical model for the problem of coercivity of nucleation controlled permanent magnets (J. Appl. Phys. {bold 64}, 6406 and 6416 (1988)), its validity to the problem of Fe-Nd-B type magnets is questioned.
  • A statistical model, based upon earlier models of Brown (J. Appl. Phys. 33, 3022 (1962)) and McIntyre (J. Phys. D 3, 1430 (1970)) has been developed to examine the magnetization reversal of domain-wall nucleation controlled permanent magnets such as sintered Fe-Nd-B and SmCo/sub 5/. Using a Poisson distribution of the defects on the surface of the grains, a ''weakest link statistics'' type model has been developed. The model has been used to calculate hysteresis loops for sintered Fe-Nd-B-type polycrystalline magnets. It is shown that the intrinsic coercivity measured for a bulk magnet should vary inversely as the logarithm of themore » surface area of the grain. The effect of demagnetizing field has been incorporated by a mean-field-type approximation, to calculate the overall nucleation field from the intrinsic coercivity. The hysteresis loops theoretically calculated are in excellent agreement with the overall form of those experimentally determined for similar nucleation controlled magnets. The model also predicts that for an inhomogeneous grain size distribution, such as a bimodal distribution, kinks will be observed in the second quadrant of the hysteresis loops.« less
  • In this work we have studied the temperature dependence of several hysteresis parameters measured in PrNdFeB samples that were obtained from melt spun amorphous precursors crystallized by employing different heating rates. Analysis of the spin reorientation temperature by means of thermal evolution of the remanence and of the demagnetization differential susceptibility revealed the presence in all samples of at least two hard 2:14:1 phases (Nd rich and Pr rich, respectively). The demagnetization curves of most samples exhibited a single magnetization reversal process thus indicating that the hard phases were coupled. Despite the multiphase character of the samples, it was possiblemore » to carry out the analysis of the temperature dependence reversal process through micromagnetic and global models, and by accepting a linear variation of the intrinsic properties with the degree of substitution of Nd by Pr. Best fits for both models were obtained when using parameters corresponding to Nd-rich 2:14:1 phases, which indicates that the collective single reversal process is driven by the Nd-rich 2:14:1 grains. {copyright} {ital 1997 American Institute of Physics.}« less