Recent developments in hard magnetic bulk materials

Abstract

The importance of newly developed permanent magnetic materials in many electromechanical, magnetomechanical and electronic applications is attributed to the drastic improvement in microstructure related properties, such as the remanence, the magnetic energy density product and the coercive field. The influence of the microstructure on the magnetic properties of the magnets will be discussed, where special emphasis is laid on rare earth permanent magnets. Highest performance, anisotropic Nd-Fe-B magnets with J r > 1.5 T, (B H) max > 450 kJ m −3 and J H c > 750 kA m −1 , which are produced by the powder metallurgy route, show a strong influence of composition and processing parameters on the magnetic properties. The magnetic properties of Sm(Co, Cu, Fe, Zr) z sintered magnets, which are used nowadays for high temperature applications between 300 and 500 • C, are determined by the cellular precipitation microstructure, which is developed during a complex heat treatment and by the microchemistry. Special hard magnetic powder materials, such as Sm 2 Fe 17 N 3 and nanocrystalline, composite Nd 2 Fe 14 B/(α-Fe, Fe 3 B) materials have been developed especially for usage in bonded magnetic materials, which show the strongest annual increase in the production of permanent magnets. The phenomenon of the enhancement of remanence, occurring in single phase and composite Nd 2 Fe 14 B based magnets with isotropic grain alignment, is attributed to intergrain exchange interactions.

Structure and properties of sintered MM–Fe–B magnets

“…4 According to the literatures, the (BH) max of Ba-ferrite and Sr-ferrite is about 5 MGOe, rare earth permanent magnet is in the range of 14∼60 MGOe. [5][6][7][8] Therefore, MMFeB magnets may fill the vacancy of (BH) max between ferrite and NdFeB.…”

Microstructural studies and micromagnetic analysis of nanocrystalline NdFeCoMB (M = Ga, Ge) melt-spun ribbon

“…In the past two decades the improvement of various magnetic properties of this alloy such as saturation magnetization (M s ), maximum energy product (BH) max , intrinsic coercive field ( i H c ), and Curie temperature have been achieved by applying various processing routes and the addition of various alloying elements. [1,2] There are two major processing routes for the production of Nd-Fe-B-based magnets; one is the powder metallurgy route for producing anistoropic sintered magnets and the other is the rapid solidification route for producing isotropic bonded magnets. Fidler et al [2,3] presented a typical category for the additives; type 2 elements such as Ga, Al, Cu, and Ge with low solubility in the Nd 2 Fe 14 B phase, which concentrate in Nd-rich phase and improve the wettability of the phase at grain boundaries and the decoupling of Nd 2 Fe 14 B grains.…”

“…[1,2] There are two major processing routes for the production of Nd-Fe-B-based magnets; one is the powder metallurgy route for producing anistoropic sintered magnets and the other is the rapid solidification route for producing isotropic bonded magnets. Fidler et al [2,3] presented a typical category for the additives; type 2 elements such as Ga, Al, Cu, and Ge with low solubility in the Nd 2 Fe 14 B phase, which concentrate in Nd-rich phase and improve the wettability of the phase at grain boundaries and the decoupling of Nd 2 Fe 14 B grains. Type 2 elements play an important role in controlling the final magnetic properties by modifying the microstructure.…”

“…Type 1 elements such as Co, Ni, Dy, and Tb modify the intrinsic magnetic properties by substituting in the Nd 2 Fe 14 B phase. [2][3][4][5] Liquid phase sintering of microcrystalline sintered Nd-Fe-B magnets and hot-compaction and deformation in nanocrystalline Nd-Fe-B magnets take place due to the existence of intergranular Nd-rich phase. This phase is mainly observed as a triple junction phase or a surrounding intergranular ultrathin layer (1 to 2 nm) in sintered Nd-Fe-B magnets.…”

[M(N3)2(H2O)2]⋅(bpeado): Unusual Antiferromagnetic Heisenberg Chain (M=Mn) and Ferromagnetic Ising Chain (M=Co) with Large Coercivity and Magnetic Relaxation (bpeado=1,2‐Bis(4‐pyridyl)ethane‐N,N′‐dioxide)

“…The large H C b of 37.5 kOe can be expected to contribute to the quite large H C powder of 17.5 kOe, which is comparable to the values for very hard magnets such as SmCo 5 or Nd 2 Fe 14 B (44 and 19 kOe, respectively, at room temperature). [25] For molecular-based materials, such a value is still quite unusual. [4, 13b, 26] Only a few molecular-based materials have hitherto been found to display such large H C values, for example, 27.8 kOe observed for [MnTBrPP]A C H T U N G T R E N N U N G [TCNE] (FI) at 2 K, [26a] 17.8 kOe for [FeA C H T U N G T R E N N U N G (dca) 2 ] (dca = dicyanamide) (FO) at 2 K, [26b] and 21.7 kOe for the Co chain compound […”