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MnBi magnetic material: A critical review

The paper summarizes the results concerning the MnBi alloys, powders and bulk magnets investigated during past 67 years. The look on the difficulties inhibiting the development of this material is given and the proposals that might allow overcoming the difficulties and push again the efforts of research towards the goal of 12 MGOe for the energy product (BH)max of MnBi bulk magnets are discussed. | Communications in Physics Vol. 29 No. 4 2019 pp. 441-454 DOI 10.15625 0868-3166 29 4 14326 MnBi MAGNETIC MATERIAL A CRITICAL REVIEW NGUYEN VAN VUONG Institute of Materials Science Vietnam Academy of Science and Technology 18 Hoang Quoc Viet Cau Giay Hanoi Vietnam Ĩ E-mail vuongnv@ims.vast.ac.vn Received 21 August 2019 Accepted for publication 12 September 2019 Published 25 October 2019 Abstract. Manganese Bismuth MnBi - the ferromagnetic material attracting a great interest of the world magnetic society last years. The absence of rare-earth elements in compositions the large magnetocrystalline anisotropy the room-temperature moderate but high-temperature reasonable magnetization plus the positive temperature coefficient of coercivity and the moderate Curie temperature make MnBi bulk magnets very potential for high-temperature magnet application. This bright future is a little gray because the research results in the past were not as expected. The paper summarizes the results concerning the MnBi alloys powders and bulk magnets investigated during past 67 years. The look on the difficulties inhibiting the development of this material is given and the proposals that might allow overcoming the difficulties and push again the efforts of research towards the goal of 12 MGOe for the energy product BH max of MnBi bulk magnets are discussed. Keywords MnBi low-temperature phase magnetization coercivity energy product bulk magnets. Classification numbers 61.05.cp 75.30.Gw 75.50.Ww 75.60.Ej. 2019 Vietnam Academy of Science and Technology 442 MnBi MAGNETIC MATERIAL A CRITICAL REVIEW I. INTRODUCTION The rare-earth-free low-cost MnBi magnets with the energy product BH mai competitive with NdFeB bonded magnets in room-temperature RT as well with NdFeB sintered magnets in high-temperature 150 - 200 C applications attract great attentions of scientific community. However despite the spent efforts the current best BH max value of MnBi bulk magnets is only 8.4 MGOe 1 a half of the .