Mn-Based Ferromagnetic Alloys
Magnetic properties of Mn-based alloys and compounds are rich in the variety of their magnetism because the magnetic moment of Mn varies from almost zero to 5 μB depending on its environment and its sign of exchange interaction changes with the distance b
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Mn-Based Ferromagnetic Alloys Yoshifuru Mitsui and Rie Y. Umetsu
Abstract Magnetic properties of Mn-based alloys and compounds are rich in the variety of their magnetism because the magnetic moment of Mn varies from almost zero to 5 lB depending on its environment and its sign of exchange interaction changes with the distance between Mn atoms. Mn-based alloys and compounds with large magnetic anisotropy are recently being focused on with regard to their applications to perpendicular magnetic films and alternate materials of permanent magnets. Although it is generally thought that magnetic anisotropy originates from large spin–orbit interaction due to heavy elements, such as Pt, Pd, and rare earth elements, some Mn-based alloys and compounds indicate comparatively large magnetic anisotropy without such heavy elements. MnAlGe pseudo-twodimensional compound with a Cu2Sb-type structure is thought to be a candidate for perpendicular magnetic films. Clarification of the mechanism of magnetic properties is needed to improve the characteristics desired for applications. MnBi has been considered to be an alternate material for permanent magnet; however, a problem exists in which a single phase of MnBi is difficult to obtain. Among some ingenious fabrication processes, it has been found that solid-state reaction in a magnetic field is effective to improve the reaction. The application of a magnetic field during the reaction enhances not only the fabrication of a single phase of MnBi but also the assembly of the crystal orientation.
Keywords Magnetic anisotropy Magnetic moment Exchange interaction In-field heat treatment
Curie temperature
Y. Mitsui (&) Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan e-mail: [email protected] R. Y. Umetsu Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan © Springer Nature Singapore Pte Ltd. 2019 Y. Setsuhara et al. (eds.), Novel Structured Metallic and Inorganic Materials, https://doi.org/10.1007/978-981-13-7611-5_4
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Y. Mitsui and R. Y. Umetsu
Introduction
Mn-based alloys and compounds have various magnetic properties. Basically, pure Mn has four phases: a, b, c, and d. The a phase has a body-center-cubic-type unit cell containing 58 Mn atoms composing four kinds of Mn sites. Its magnetism is antiferromagnetic having a Néel temperature of 95 K [1]. Although the ground state of the b phase is enhanced Pauli paramagnetism, antiferromagnetic ordering or spin-glass-like-magnetism is induced by substitution of elements, such as Al, Co, Ru, Rh, and Os [2, 3]. The crystal structure is also cubic type with 20 Mn atoms in the unit cell and it has two kinds of inequivalent Mn sites. The c phase is a face-centered-cubic structure and shows paramagnetism at around 1100 K. It is hard to obtain the c phase at room temperature by quenching of pure Mn; however, stabilization is possibly by substitution of certain elements, and the obtained phase exhibits antiferrom
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