Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

Journal Article · Mon May 09 00:00:00 EDT 2016 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4948933· OSTI ID:22591712

Taylor, A. E.; Lumsden, M. D. ^[1]; Christianson, A. D. ^[1]; Hahn, S. E. ^[2]; Fishman, R. S.; Parker, D. S.; McGuire, M. A.; Sales, B. C. ^[3]

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1. Quantum Condensed Matter Division, Neutron Sciences Directorate, Oak Ridge National Lab, Oak Ridge, Tennessee 37831 (United States)
2. Neutron Data Analysis and Visualization Division, Neutron Sciences Directorate, Oak Ridge National Lab, Oak Ridge, Tennessee 37831 (United States)
3. Materials Science and Technology Division, Physical Sciences Directorate, Oak Ridge National Lab, Oak Ridge, Tennessee 37831 (United States)

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 parametrize 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.

• OSTI ID: 22591712
• Journal Information: Applied Physics Letters, Vol. 108, Issue 19; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANTIFERROMAGNETISM
COERCIVE FORCE
CRYSTALS
CURIE POINT
EXCHANGE INTERACTIONS
GROUND STATES
HEISENBERG MODEL
INELASTIC SCATTERING
INTERACTION RANGE
MAGNETIC MOMENTS
NEUTRON DIFFRACTION
NEUTRON REACTIONS
PERMANENT MAGNETS
RARE EARTHS
RESOLUTION
SPIN
SPIN WAVES
SYNTHESIS
TEMPERATURE RANGE 0400-1000 K