Enhanced Mr and (BH)max in anisotropic R2Fe14B∕α-Fe composite magnets via intergranular magnetostatic coupling

Abstract

Composite magnets were prepared by hot pressing followed by hot deformation of blends composed of Nd14Fe79.5Ga0.5B6 or (Nd0.75Dy0.25)14Fe79.5Ga0.5B6 ribbon powders as a high-coercivity component and Fe powder as a high-magnetization component. The addition of 15 wt % α-Fe to (Nd0.75Dy0.25)14Fe79.5Ga0.5B6 increases the remanent magnetization of the hot-deformed magnets from 10.6 to 12.04 kG, while the maximum energy product is also increased from 27.3 to 29.5 MG Oe for hot-deformed magnets with 10 wt % α-Fe addition. Microstructure investigations of the composite magnets revealed the size of the Fe particles in the micrometer range, exceeding by far the size for effective exchange interactions. Despite a less refined microstructure, the particular layered configuration of the composite magnets gives rise to a positive magnetostatic coupling of the grains and therefore a unitary magnetic behavior with enhanced magnetic properties. The cooperative demagnetization process, together with the magnetic coupling of the grains, was pointed out through a smooth demagnetization curve and a sharp single peak of the irreversible susceptibility.

Effect of Mo interlayer on magnetic properties of exchange coupled Sm-Co/Fe bilayers

“…This type of magnets is named as spring exchange magnets. In spring exchange magnets, soft and hard phases are exchange coupled with each other at certain grain sizes which are usually around 10 nm [1][2][3]. In such conditions of soft and hard phases, the hysteresis loop becomes like a single phase magnet.…”

“…Spring exchange magnets have been prepared by mechanical milling [6], melt spinning [1], sputtering [7,8] and by chemical method [9]. Among these techniques sputtering has advantage to have well control on the thickness of soft and hard phases because layer thickness is basic parameter to get strong exchange coupling between the two phases.…”

Spark Plasma Sintered NdFeB-based Nanocomposite Hard Magnets with Enhanced Magnetic Properties

“…The strength of the decoupling is indicated by the second shoulder of dM/dH=f(H) curves located nearby Y axis, which is very small for SPS consolidated nanocomposite magnets, but also by the height of the first peak. In this case, it is hard to believe that only the intergranular exchange coupling is responsible for such behaviour, but most probably a collective process of both exchange and magnetostatic interactions between the powders of the 2 materials forming the nanocomposite (Gabay et al, 2006). The same behavior is observed for Nd16 powders and nanocomposite magnets, as indicated in Fig.…”

Magnetostatically-Coupled Anisotropic Composite Magnets with Enhanced Remanence

“…In the model [1], a magnet was represented by a 3D array of uniformly magnetized cube-shaped elements. Both the magnetization and magnetic field were assumed to be parallel to the common easy magnetization direction z.…”

“…This requirement is set by the short range of magnetic exchange interactions, which are meant to be responsible for the magnetic coupling between the hard and soft magnetic phases. However, recent experiments [1,2] on composite magnets prepared by hot-pressing and hot-deformation of blends of crushed nanocrystalline R 2 Fe 14 B melt-spun ribbons (where R is rare earth) and micron-size iron powders, suggested that the magnetic coupling between the hard and soft phases can also be in much coarser structures. The magnetic coupling in these composite systems is a long-range magnetostatic coupling ensured by a specific layered morphology formed during the hotdeformation process.…”