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



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 A. Borchers, Brian J. Kirby, Brian B. Maranville, K. W. Sun, M. J. Kramer, V. P. Antropov, D. D. Johnson, R. Skomski, J. Cui, I. Takeuchi


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.
Physical Review B


permanent magnet, exchange spring, polarized neutron reflectivity, energy product
Created August 29, 2016, Updated February 19, 2017