Materials Science Centre, Indian Institute of Technology, Kharagpur-721 302, India.
Nanotechnology. 2023 Jun 1;34(33). doi: 10.1088/1361-6528/acd34c.
The MnBi alloys is a model series of rare-Earth free magnets for surge of technologies of small parts of automobiles, power generators, medical tools, memory systems, and many others. The magnetics stem primarily at unpaired Mn-3dspins (a 4.23moment) align parallel via an orbital moment 0.27of Bi-5d6spin a crystal lattice. Thus, using a surplus Mn (over Bi) in a MnBitype alloy designs a spin-rich system of duly tailored properties useful for magnetics and other devices. In this view, we report here a strategy of a refined alloy powder MnBican grow into small crystals of hexagonal (h) plates at seeds as annealed in magnetic fields (in Hgas). So, small h-plates (30 to 50 nm widths) are grown up at (002) facets, wherein the edges are turned down in a spiral (≤2.1 nm thicknesses) in a core-shell structure. The results are described with x-ray diffraction, lattice images and magnetic properties of a powder MnBi(milled in glycine) is annealed at 573 K for different time periods, so to the Mn/Bi order at the permeable facets (seeds). Duly annealed samples exhibit an enhanced magnetization,→ 70.8 emu g, with duly promoted coercivity→ 10.810 kOe (15.910 kOe at 350 K), energy-product 14.8 MGOe, and the crystal-field-anisotropy,→ 7.6 × 10erg cm, reported at room temperature. Otherwise,should decline at any surplus 3d-Mn spins order antiparallel at the antisites. Enhanced Curie point 658.1 K (628 K at MnBialloy) anticipates that a surplus Mn does favor the Mn-Bi exchange interactions. Proposed spin models well describe the spin-dynamics and lattice relaxations (on anneals) over the lattice volume (with twins) and spin clusters.
MnBi 合金是一类无稀土永磁体的模型系列，可用于汽车零部件、发电机、医疗工具、存储系统等众多技术领域的发展。该磁体主要由未配对的 Mn-3d 自旋（4.23 磁矩）通过晶体晶格中 0.27 的 Bi-5d6 自旋轨道矩平行排列而成。因此，在 MnBi 型合金设计中使用过量的 Mn（相对于 Bi）可以形成具有适当特性的富含自旋的系统，从而可用于磁性和其他器件。在这种情况下，我们在此报告了一种细化合金粉末 MnBi 的策略，使其在磁场（在 Hgas 中）退火后能够生长成小的六方（h）片状晶体。因此，小的 h 片状晶体（30 至 50nm 宽度）在（002）晶面上生长，其边缘呈螺旋状下降（<2.1nm 厚度），形成核壳结构。通过 X 射线衍射、晶格图像和磁性对在不同时间段退火的 MnBi（在甘氨酸中研磨）粉末的研究，描述了 Mn/Bi 在可渗透晶面（种子）处的有序性。适当退火的样品表现出增强的磁化强度，→70.8emu/g，矫顽力相应提高，→10.810kOe（在 350K 时为 15.910kOe），能量积 14.8MGOe，以及在室温下报道的晶体场各向异性，→7.6×10erg/cm。否则，在反位处任何过量的 3d-Mn 自旋的反平行有序都会导致其降低。居里点 658.1K（MnBi 合金为 628K）表明，过量的 Mn 有利于 Mn-Bi 交换相互作用。所提出的自旋模型很好地描述了自旋动力学和晶格弛豫（在退火时）在晶格体积（孪晶）和自旋团簇上的变化。
