Anisotropic nanocrystalline MnBi with high coercivity at high temperature

Yang, Jyh‐Shinn; Yang, Yunbo; Chen, X. G.; Ma, Xiaobai; Han, Jiayu; Yang, Yingchang; Guo, Shuai; Yan, Aru; Huang, Q.; Wu, Mei; Chen, D. F.

doi:10.1063/1.3630001

Cited by 121 publications

(97 citation statements)

References 15 publications

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“…Signatures of this coupling have been reported in the temperature dependence of the lattice constants of MnBi [22,26,27]. While the hexagonal NiAs structure type describes the powder xray diffraction results at all temperatures, anomalies in both the a and c lattice parameters occur at temperatures near the spin reorientation.…”

Section: Introductionmentioning

confidence: 95%

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

et al. 2014

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Structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi are reported. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature TSR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropy of the atomic displacement parameters for Bi with increasing temperature above TSR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. The identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.

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Section: Introductionmentioning

confidence: 95%

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

et al. 2014

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“…MnBi is an attractive alternative to the permanent magnets containing rare earth elements, especially the ones for medium temperature applications (423-473 K) such as Nd-Fe-B-Dy and Sm-Co. MnBi has attractive temperature properties: its coercivity increases with increasing temperature, reaching a maximum of 2.6 T at 523 K [1][2][3][4]. The high coercivity is attributed to MnBi's large magnetocrystalline anisotropy (1.6 × 10 6 J m −3 ) [5].…”

Section: Introductionmentioning

confidence: 99%

Thermal stability of MnBi magnetic materials

Cui

Choi

et al. 2014

J. Phys.: Condens. Matter

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MnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase material for exchange coupling nanocomposite magnets. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. MnO formation is irreversible and harmful to magnet performance. In this paper, we report our efforts toward developing MnBi permanent magnets. To date, high purity MnBi (>90%) can be routinely produced in large quantities. The produced powder exhibits 74.6?emu?g?1 saturation magnetization at room temperature with 9?T applied field. After proper alignment, the maximum energy product (BH)max of the powder reached 11.9?MGOe, and that of the sintered bulk magnet reached 7.8?MGOe at room temperature. A comprehensive study of thermal stability shows that MnBi powder is stable up to 473?K in air. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. AbstractMnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase material for exchange coupling nanocomposite magnets. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. MnO formation is irreversible and harmful to magnet performance. In this paper, we report our efforts toward developing MnBi permanent magnets. To date, high purity MnBi (>90%) can be routinely produced in large quantities. The produced powder exhibits 74.6 emu g −1 saturation magnetization at room temperature with 9 T applied field. After proper alignment, the maximum energy product (BH) max of the powder reached 11.9 MGOe, and that of the sintered bulk magnet reached 7.8 MGOe at room temperature. A comprehensive study of thermal stability shows that MnBi powder is stable up to 473 K in air.

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“…4 Therefore, there have been intense research efforts in identifying and developing novel rare-earth free high-anisotropy magnets. Some of the non-rare-earth-element-based permanent magnet materials of current interest are the manganese-based ferromagnetic materials including MnBi, 5,6 MnAl, 7 and MnGa. [8][9][10] Among these three magnets, Mn y Ga is particularly interesting because its magnetic properties can be tuned by varying y to fit specific magnetic and magnetoelectronic applications.…”

Section: Introductionmentioning

confidence: 99%

Magnetism and electron transport of MnyGa (1 < y < 2) nanostructures

Huh

Kharel

Shah

et al. 2013

Journal of Applied Physics

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Nanostructured Mn y Ga ribbons with varying Mn concentrations including Mn 1.2 Ga, Mn 1.4 Ga, Mn 1.6 Ga, and Mn 1.9 Ga were prepared using arc-melting and melt-spinning followed by a heat treatment. Our experimental investigation of the nanostructured ribbons shows that the material with y ¼ 1.2, 1.4, and 1.6 prefers the tetragonal L1 0 structure and that with y ¼ 1.9 prefers the D0 22 structure. We have found a maximum saturation magnetization of 621 emu/cm 3 in Mn 1.2 Ga which decreases monotonically to 300 emu/cm 3 as y reaches 1.9. Although both the L1 0 -and D0 22 -Mn y Ga samples show a high Curie temperature (T c ) well above room temperature, the value of T c decreases almost linearly from 702 K for Mn 1.9 Ga to 551 K for Mn 1.2 Ga. All the ribbons are metallic between 2 K and 300 K but the Mn 1.2 Ga also shows a resistance minimum near 15 K. The observed magnetic properties of the Mn y Ga ribbons are consistent with the competing ferromagnetic coupling between Mn moments in the regular L1 0 -MnGa lattice sites and antiferromagnetic coupling with excess Mn moments occupying Ga sites. V C 2013 AIP Publishing LLC. [http://dx

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Anisotropic nanocrystalline MnBi with high coercivity at high temperature

Cited by 121 publications

References 15 publications

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

Thermal stability of MnBi magnetic materials

Magnetism and electron transport of MnyGa (1 < y < 2) nanostructures

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Anisotropic nanocrystalline MnBi with high coercivity at high temperature

Cited by 121 publications

References 15 publications

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

Thermal stability of MnBi magnetic materials

Magnetism and electron transport of MnyGa (1 &lt; y &lt; 2) nanostructures

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Product

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Magnetism and electron transport of MnyGa (1 < y < 2) nanostructures