Twins – A weak link in the magnetic hardening of ThMn12-type permanent magnets

Abstract

Nd2Fe14B-type materials exhibit the highest energy product around room temperature and hence dominate the high-performance permanent magnet market. Intensive research efforts aim at alternative material systems containing less critical elements with similar or better magnetic properties. Nd-and Sm-based compounds with a ThMn12-type structure exhibit intrinsic properties comparable or even superior to Nd2Fe14B. However, it has not been possible to achieve technically relevant coercivity and remanent magnetization in ThMn12-based bulk sintered magnets. Using SmFe11Ti as a prototypical representative, we demonstrate that one important reason for the poor performance is the formation of twins inside micro-crystalline grains. The nature of the twins in SmFe11Ti was investigated in twinned "single crystals" and both bulk and thin film poly-crystalline samples, using advanced electron microscopy and atom probe tomography as well as simulations and compared with benchmark Nd2Fe14B. Both micro-twins and nano-twins show a twin orientation of 57±2 • and an enrichment in Sm, which could affect domain wall motion in this 2 material. Micromagnetic simulations indicate that twins act as nucleation centers, representing the magnetically weakest link in the microstructure. The relation between twin formation energies and geometrical features are briefly discussed using molecular dynamic simulations.

Intrinsically High Magnetic Performance in Core–Shell Structural (Sm,Y)Fe12‐Based Permanent Magnets

“…[1][2][3][4] ThMn 12 -type SmFe 12 -based permanent magnets have been recognized as the promising one of potential candidates because of their intrinsically high temperature stability of magnetic properties. [5][6][7][8][9][10][11] However, because of the metastable enhanced pinning effect of domain walls of magnetic hardening shells. [24,25] For the ThMn 12 -type alloys, Tozman et al recently proposed the first core-shell structure composed of Gd-rich shell and Gd-lean core in the (Sm,Gd)Fe 12 -based alloys.…”

“…[ 1–4 ] ThMn 12 ‐type SmFe 12 ‐based permanent magnets have been recognized as the promising one of potential candidates because of their intrinsically high temperature stability of magnetic properties. [ 5–11 ] However, because of the metastable characteristics, it still remains a challenge to achieve the single phase structure of SmFe 12 system in bulk magnets. [ 11,12 ]…”

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characteristics, it still remains a challenge to achieve the single phase structure of SmFe 12 system in bulk magnets. [11,12] It has been proven that a certain amount of additives of non-magnetic stable elements M (M = Ti, V, Cr, Si, Al, Ga, etc.) could effectively improve the stability of Sm(Fe, M) 12 phases.

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Structure and Magnetic Properties of Intermetallic Rare-Earth-Transition-Metal Compounds: A Review

“…The microstructure must allow reaching the highest possible coercivity and remanent induction and a magnetization loop close to a rectangular one. The achievement of each of these objectives is facilitated by the existence of a granular microstructure [ 2 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”

Effect of transition metal doping on magnetic hardness of CeFe$_{12}$-based compounds

“…Of particular interest are rare-earth compounds such as Nd 2 Fe 14 B [1] and SmCo 5 [2] showing extremely high values of magnetocrystalline anisotropy. However, the high volatility of rare earth prices that became clearly evident during the so-called rare-earth crisis of 2011 [3] has mobilized the international research community to search for a new generation of hard magnetic materials with reduced rare-earth content [4][5][6][7][8][9][10]. These explorations, although mostly performed by experimental methods, are complemented by the efforts of groups conducting first-principles calculations of intrinsic properties and magnetic simulations at the microstructural level.…”