Magnetic-field-enhanced reactive synthesis of MnBi from Mn nanoparticles

Si, Peng; Yang, Yingchang; Yao, Lulu; Qian, Hui-Dong; Ge, Hongliang; Park, J.; Chung, Kookchae; Choi, Chul-Jin

doi:10.1016/j.jmmm.2018.12.077

Cited by 23 publications

(14 citation statements)

References 23 publications

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“…As given in table 2, a low value of M s = 20.5 emu g −1 obtained at 300 K in the master alloy has increased to 72.5 emu g −1 for a sample annealed for 96 h at 573 K. A marginally lower 70.0 emu g −1 is measured at 325 K, and 67.4 emu g −1 is recorded at 350 K, with a small thermal coefficient, β = (∂M s /∂T)M s −1 ∼ = −0.14% K −1 , in terms of heat induced spin relaxations. These are better M s values in comparison to other reported high H c values (compared in table 3) achieved using refined alloys of small crystallites [9,26,27,[28][29][30][31], which usually lose M s on canted (or SPM) surface spins.…”

Section: Magnetic Properties Of Mncontrasting

confidence: 47%

“…In a micromagnetic model, Bi-p 3 interlocks Mnd 5 (of unpaired spins) in a hybrid spring magnet on hybridized p-d electrons, which advances its thermal stability and anisotropic magnetic properties, as observed for the annealed samples. In general, Bi-p 3 spins occur in opposition to Mn-d 5 in a ferrimagnet, Mn 0.5+x Bi 0.5−x , x ⩽ 0.05, which successfully describes its highly variable M s = 22 to 81 emu g −1 , as observed at 295 K when prepared using different routine methods [14,[28][29][30][31]. Any excess Mn clots in an AFM blister (i.e.…”

Section: Discussionmentioning

confidence: 80%

“…Further, MnBi nanocrystals deduced by co-reducing Mn 2+ /Bi 3+ salts in a liquid bath exhibit M s = 49.0 emu g −1 and H c = 15.0 kOe [28,29]. A reactive sintering of the Mn and Bi small particles of a Mn 0.55 Bi 0.45 alloy yields a lower H c ⩽ 8.0 kOe [30]. A larger H c = 16.3 kOe, but a far lower M s = 22.0 emu g −1 , occurs in the composite alloy of MnBi-Bi generated by a calciothermic Mn-Bi 2 O 3 reduction in Ar gas [31].…”

Section: Introductionmentioning

confidence: 96%

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Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

Sharma¹,

Ram²,

Pradhan³

2020

Nanotechnology

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The binary alloy Mn0.5+xBi0.5−x, x ⩽ 0.05, is a promising rare-earth-free magnetic material, with high-energy-density (a critical characteristic for electric motors and power electronics), low cost, and significant magnetic properties for multiple uses at room temperature. In this article, we report how a free Bi, when precipitated over Mn0.5+xBi0.5−x (x ⩽ 0.05) of small crystallites, diffuses back into a stable Mn0.5+xBi0.5−x, x → 0, via a peritectic reaction, which facilitates preferential growth of small core–shell crystallites with multiple facets, having the potential for tailored magnetic properties. This growth travels slowly in the anisotropic channels of vacancies on annealing the reactive nanopowder at a critical 573 K temperature in Ar gas. Thus, an initial crystallite size of D ∼ 27 nm grows to only 38 nm in a reaction extended over a period of 96 h. A transient phase, x > 0, which has Bi vacancies, primarily grows in the (101) and (110) facets, filling the vacancies over a 6.41% larger crystal density. If any excess Mn is present, it segregates over a saturated phase, combines with free Bi, and ultimately forms a stable alloy phase. The small crystallites contain an inbuilt surface Bi-layer (shell), with a 1–2 nm thickness, in a core–shell of nanoplates (20–60 nm width), as shown in the high resolution transmission electron microscope images. In the proposed microscopic model, with hybridized Mn-d5 and Bi-p3 electrons (also spins), the magnetic properties are readily controlled. Thus, at 300 K, a maximum coercivity Hc = 9.850 kOe (14.435 kOe at 350 K) develops (Hc = 5.010 kOe in the initial) in critical single domains (D ∼ 33 nm). A net 72.5 emu g−1 magnetization occurs, with an enhanced TC = 641.5 K (600.5 K at x ∼ 0.05) on an order of enhanced anisotropy constant K1, demonstrating the significant effects of this core–shell structure of small crystallites.

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Section: Magnetic Properties Of Mncontrasting

confidence: 47%

Section: Discussionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 96%

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Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

Sharma¹,

Ram²,

Pradhan³

2020

Nanotechnology

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“…It presents profound engineering properties at small clusters of single magnetic domains (SMDs) in three major forms; bulk, thin films, and nano-architects (NAs). Traditionally, it is believed to form and exist of a line compound Mn 50 Bi 50 of crystallites at equal Mn/Bi atoms [9][10][11][12][13][14][15][16][17]. Then, a question arises how a Mn/Bi ratio keeps as the atoms converge at surfaces at NAs in small clusters [19,22].…”

Section: Introductionmentioning

confidence: 99%

A core–shell magnet Mn₇₀Bi₃₀ grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties

2023

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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-3d5 spins (a 4.23 B moment) align parallel via an orbital moment 0.27 B of Bi-5d106s2p3 in a crystal lattice. Thus, using a surplus Mn (over Bi) in a Mn70Bi30 type 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 Mn70Bi30 can grow into small crystals of hexagonal (h) plates at seeds as annealed in magnetic fields (in H2 gas). 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 Mn70Bi30 (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, Ms  70.8 emu/g, with duly promoted coercivity Hc  10.810 kOe (15.910 kOe at 350 K), energy–product 14.8 MGOe, and the crystal-field-anisotropy, K1  7.6x107 erg/cm3, reported at room temperature. Otherwise, Ms should decline at any surplus 3d5-Mn spins order antiparallel at the antisites. Enhanced Curie point 658.1 K (628 K at Mn50Bi50 alloy) 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.

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“…Consequently, the addition of secondary elements or materials, such as Ga (e.g., Mn 55 Bi 44 Ga) [ 12 ], Sn (e.g., MnBi 1- x Sn x ) [ 13 ], NaCl or C [ 14 ], and nanoparticles [ 15 ], to MnBi has been investigated in efforts to increase the H c . Furthermore, magnetic field annealing has been used to enhance the magnetic properties for permanent magnet applications [ 16 , 17 , 18 , 19 , 20 , 21 ].…”

Section: Introductionmentioning

confidence: 99%

Effects of Mg and Sb Substitution on the Magnetic Properties of Magnetic Field Annealed MnBi Alloys

et al. 2020

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Rare-earth-free permanent magnets have attracted considerable attention due to their favorable properties and applicability for cost-effective, high-efficiency, and sustainable energy devices. However, the magnetic field annealing process, which enhances the performance of permanent magnets, needs to be optimized for different magnetic fields and phases. Therefore, we investigated the effect of composition on the crystallization of amorphous MnBi to the ferromagnetic low-temperature phase (LTP). The optimal compositions and conditions were applied to magnetic field annealing under 2.5 T for elemental Mg- and Sb/Mg pair-substituted MnBi. The optimum MnBi composition for the highest purity LTP was determined to be Mn56Bi44, and its maximum energy product, (BH)max, was 5.62 MGOe. The Mg-substituted MnBi exhibited enhanced squareness (Mr/Ms), coercivity (Hc), and (BH)max values up to 0.8, 9659 Oe, and 5.64 MGOe, respectively, whereas the same values for the Sb/Mg pair-substituted MnBi were 0.76, 7038 Oe, and 5.60 MGOe, respectively. The substitution effects were also investigated using first-principles calculations. The density of states and total magnetic moments of Mn16Bi15Mg and Mn16Bi15Sb were similar to those of pure Mn16Bi16. Conversely, the Sb-substituted MnBi resulted in a dramatic enhancement in the anisotropy constant (K) from a small negative value (−0.85 MJ/m3) to a large positive value (6.042 MJ/m3).

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Magnetic-field-enhanced reactive synthesis of MnBi from Mn nanoparticles

Cited by 23 publications

References 23 publications

Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

A core–shell magnet Mn₇₀Bi₃₀ grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties

Effects of Mg and Sb Substitution on the Magnetic Properties of Magnetic Field Annealed MnBi Alloys

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Magnetic-field-enhanced reactive synthesis of MnBi from Mn nanoparticles

Cited by 23 publications

References 23 publications

Small core–shell Mn0.5Bi0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

Small core–shell Mn0.5Bi0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

A core–shell magnet Mn70Bi30 grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties

Effects of Mg and Sb Substitution on the Magnetic Properties of Magnetic Field Annealed MnBi Alloys

Contact Info

Product

Resources

About

Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

Small core–shell Mn_0.5Bi_0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

A core–shell magnet Mn₇₀Bi₃₀ grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties