Large Energy Product Enhancement in Perpendicularly Coupled MnBi/CoFe Magnetic Bilayers

Published

August 29, 2016

Author(s)

T. R. Gao, L. Fang, S. Fackler, S. Maruyama, X. H. Zhang, L. L. Wang, T. Rana, P. Manchanda, A. Kashyap, K. Janicka, A. L. Wysocki, A. T. N'Diaye, E. Arenholz, Julie Borchers, Brian Kirby, Brian B. Maranville, K. W. Sun, M. J. Kramer, V. P. Antropov, D. D. Johnson, R. Skomski, J. Cui, I. Takeuchi

Abstract

Finding rare-earth free alternatives to Nd and Sm based permanent magnets has emerged as an urgent technological challenge due to the global economic impact of price instability of rare-earth elements. Among possible candidates, MnBi is one of the few compounds with appreciable intrinsic magnetocrystalline anisotropy. Unfortunately, its low magnetization intrinsically limits the maximum energy product needed for many applications. Here, we demonstrate substantial enhancement in the energy product of MnBi based magnets by forming robust ferromagnetic exchange coupling between MnBi and a thin Co layer in a unique perpendicular coupling configuration, which provides increased resistance to magnetization reversal. The measured nominal energy product of 200 kJ/m³ at room temperature is the largest value attained for permanent magnets free of expensive raw materials. Our finding shows that exchange-coupled MnBi/Co magnets are a viable option for pursuing rare-earth-free magnets with energy products approaching those containing rare earth elements.

Citation

Physical Review B

Volume

94

Issue

6

Pub Type

Journals

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Keywords

permanent magnet, exchange spring, polarized neutron reflectivity, energy product

Citation

Gao, T. , Fang, L. , Fackler, S. , Maruyama, S. , Zhang, X. , Wang, L. , Rana, T. , Manchanda, P. , Kashyap, A. , Janicka, K. , Wysocki, A. , N'Diaye, A. , Arenholz, E. , Borchers, J. , Kirby, B. , Maranville, B. , Sun, K. , Kramer, M. , Antropov, V. , Johnson, D. , Skomski, R. , Cui, J. and Takeuchi, I. (2016), Large Energy Product Enhancement in Perpendicularly Coupled MnBi/CoFe Magnetic Bilayers, Physical Review B, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=918650 (Accessed October 27, 2025)