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Title: Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

Abstract

Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.

Authors:
 [1];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1252153
Alternate Identifier(s):
OSTI ID: 1252115
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 108; Journal Issue: 19; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ferromagnetic materials; spin waves; antiferromagnetism; curie point; exchange interactions

Citation Formats

Christianson, Andrew D., Hahn, Steven E., Fishman, Randy Scott, Parker, David S., McGuire, Michael A., Sales, Brian C., Lumsden, Mark D., Williams, T. J., and Taylor, A. E. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi. United States: N. p., 2016. Web. doi:10.1063/1.4948933.
Christianson, Andrew D., Hahn, Steven E., Fishman, Randy Scott, Parker, David S., McGuire, Michael A., Sales, Brian C., Lumsden, Mark D., Williams, T. J., & Taylor, A. E. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi. United States. doi:10.1063/1.4948933.
Christianson, Andrew D., Hahn, Steven E., Fishman, Randy Scott, Parker, David S., McGuire, Michael A., Sales, Brian C., Lumsden, Mark D., Williams, T. J., and Taylor, A. E. Mon . "Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi". United States. doi:10.1063/1.4948933. https://www.osti.gov/servlets/purl/1252153.
@article{osti_1252153,
title = {Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi},
author = {Christianson, Andrew D. and Hahn, Steven E. and Fishman, Randy Scott and Parker, David S. and McGuire, Michael A. and Sales, Brian C. and Lumsden, Mark D. and Williams, T. J. and Taylor, A. E.},
abstractNote = {Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.},
doi = {10.1063/1.4948933},
journal = {Applied Physics Letters},
number = 19,
volume = 108,
place = {United States},
year = {2016},
month = {5}
}

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Cited by: 10 works
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Figures / Tables:

FIG. 1. FIG. 1.: (Color online) The crystal structure of MnBi. The Mn atoms (small, blue) occupy the 2a position, while the Bi atoms (large, red) occupy the 2c position. The other half of the interstitial positions (Wyckoff symbol 2d), shown as open circles, can be occupied by Mn impurities. Charac- terizationmore » measurements of the samples used suggested that 1(1) % of the interstitial sites were so occupied by Mn atoms5. The spin arrangement shown is for the low-temperature range (T < 90 K). At all temperatures, MnBi is ferromagnetic, how- ever above T = 140 K, the spins point atlong the c-axis, while from T = 140 K to 90 K, the spins rotate away from the c- axis such that below 90 K the spins lie entirely in the ab-plane. The exchange parameters (J1 through J6) determined in this work are shown between the relevant Mn ions.« less

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    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.