The effects of Co on the enhancement of magnetic properties by modifying the intergranular phase in Nd-Fe-B alloys

Abstract

In Nd2Fe14B-based permanent materials, the intergranular phase has a strong influence on magnetic properties. Here, we study the effect of partial substitution of Fe by Co on the microstructure to gain insight into the mechanism of enhancing magnetic properties of (Nd0.8Pr0.2)2.2Fe14−xCoxB (x = 0, 1.75, 2, 2.25) alloys. Our results show that the substitution Co for Fe changes the magnetic properties obviously by tuning the chemistry and distribution of the intergranular phase between hard magnetic grains. In particular, for (Nd0.8Pr0.2)2.2Fe12Co2B (x = 2) alloy, no obvious intergranular phase is observed. And the through-thickness homogeneity and ultrafine microstructure with an average size of ~25 nm is obtained, which produces maximum product ((BH)max) of 141 kJ/m3, 29% higher than that of quaternary alloy. Our findings provide a new idea to design prospective permanent alloys with increased magnetic properties by tuning the distribution and chemical composition of the intergranular phase.

Structural ordering at magnetic seeds with twins at boundaries of a core–shell alloy Mn60Bi40 and tailored magnetic properties

“…So, it favors them usable over a wide range of temperatures, especially, near room temperatures, safely at500 K [3][4][5][6][7]. They have superior erosion resistance to protect stable properties at uses in ambient air [8][9][10][11][12][13][14][15]. In this view, such alloys in general are preferably eco-friendly for uses as small magnets, servo motors, automobiles, recording media, spintronics, MEMS (micro-electro-mechanical systems), microelectronics, biomedical tools, and other possible devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

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

“…Hierarchical microscopic assemblies (or clusters) of randomly aligned anisotropic crystallites of single ferromagnetic (FM) domains have been found to exhibit promising magnetic properties, in terms of coercivity H c , remnant magnetization M r , and energy-density (BH) max in a wide hysteresis loop, owing to the control exerted by collective spin dynamics over magnetocrystalline (K 1 ), shape (H a ), and surface (H s ) anisotropies in individual crystallites [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Geometrical shapes, cleaved facets, configuration of surface spins, lattice defects, and twined boundaries are vital variants required to tailor the nontrivial microscopic features of the collective spin dynamics of single domains, and mutual exchange interactions between tiny modules in a cluster, at a wider length scale in the nanometer-to-submicrometer range.…”

“…Magnetic materials are a clean-energy source, with widetranmging applications such as power generators, electric motors, micro-electro-mechanical systems (MEMS), power electronics, automobiles, medicine, wind turbines, sensors, and magnetic valves [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In particular, the rare-earthfree alloy, Mn 0.45+x Bi 0.55−x , 0 ⩽ x ⩽ 0.10, has been intensively studied as an alternative magnetic material to replace Nd 2 Fe 14 B [5,17] and SmCo 5 [5,14], in view of the relative scarcity and higher costs of the rare earth metals employed in the alloys for these types of powerful magnets [12][13][14]. Here, Mn-3d 5 spins occupy only just under half of the net interstices, x ⩽ 0.10, in a NiAs-type hexagonal crystal lattice (P6 3 /mmc space group) of an F order, which shares a net spin magnetic moment µ s = 3.84 µ B per Mn atom (81.3 emu g −1 ) [13,14].…”

Accelerated discovery of cost-effective Nd–Fe–B magnets through adaptive learning

“…Efforts towards doping (substituting) elements with lower cost, such as La, Ce, and Y to partially replace Nd, and leveraging the temperature stability with Co have been underway for decades. 19–22 La and Ce are more abundant and less costlier than Nd, yet the intrinsic magnetic properties of La 2 Fe 14 B/Ce 2 Fe 14 B (for example, saturation magnetization M r , magnetocrystalline anisotropy field H a , and Curie temperature T C ) are inferior to those of Nd 2 Fe 14 B. 2 As a result, doping of La/Ce invariably leads to degraded magnetic properties, especially at HT.…”

“…22–29 Co, with a very high T C , could significantly improve the temperature stability and therefore benefit HT magnetic properties, although it results in loss of RT magnetic properties as well. 21,30–33 In recent years, investigation of Y as a promising doping species for Nd–Fe–B has picked up momentum. Although Y fails to rise above La and Ce in terms of M r and H a , Y 2 Fe 14 B demonstrates a higher T C than La 2 Fe 14 B or Ce 2 Fe 14 B, as well as a positive temperature coefficient of H a over a wide temperature range, rendering it a promising candidate for enhanced HT magnetic properties.…”