The microstructure, high performance magnetic hardness and magnetic after-effect of an α- FeCo/Pr₂Fe₁₄B nanocomposite magnet with low Pr concentration

Abstract

In this paper, a systematic investigation of the microstructure, high performance magnetic hardness as well as novel magnetic memory effect of the Pr(4)Fe(76)Co(10)B(6)Nb(3)Cu(1) nanocomposite magnet fabricated by conventional melt-spinning followed by annealing at temperatures ranging from 600 to 700 degrees C in Ar gas for nanocrystallization are presented and discussed. Transmission electron microscopy (TEM) observation confirms an ultrafine structure of bcc-Fe(Co) as a magnetically soft phase and Pr(2)Fe(14)B as a hard magnetic phase with a spring-exchange coupling in order to form the nanocomposite state. Electron diffraction analysis also indicates that the Co atoms together with Fe atoms form the Fe(70)Co(30) phase with a very high magnetic moment (2.5 mu(B)), leading to a high saturation magnetization of the system. High magnetic hardness is obtained in the optimally heat-treated specimen with coercivity H(c) = 3.8 kOe, remanence B(r) = 12.0 kG, M(r)/M(s) = 0.81 and maximum energy product (BH)(max) = 17.8 MG Oe, which is about a 25% improvement in comparison with recent results for similar compositions. High remanence and reduced remanence are the key factors in obtaining the high performance with low rare-earth concentration (only 4 at.%). High-resolution TEM analysis shows that there is a small amount of residual amorphous phase in the grain boundary, which plays a role of interphase to improve the exchange coupling. Otherwise, in terms of magnetic after-effect measurement, a magnetic memory effect was observed for the first time in an exchange-coupled hard magnet.

Investigation on intergranular exchange coupling effect in Pr9Fe85.5B5.5 ribbons

“…[2][3][4][5][6][7] The effect of exchange coupling varies widely due to its strong dependence on the intrinsic interfacial nature, grain size, exchange coefficient, and magnetocrystalline anisotropy. [8][9][10][11][12][13][14][15][16] Actually, exchange coupling exists not only between soft-hard grains resulting in a strong resistance against magnetization reversal in soft grains 1 but also between hard-hard grains leading to more uniform magnetization behaviors. 17 The intergranular exchange coupling effect, even investigated extensively, remains unclear to some degree due to its complicated feature in nanocomposite magnets.…”

“…It is believed that exchange coupling at interface is enhanced owing to the amorphous grain boundaries. [9][10][11] In sample C, owing to the higher quenching rate in melt spinning, the content of residual interfacial amorphous phase is a little more than in sample B. According to Scherrer formula, it is estimated that the average grain sizes of Pr 2 Fe 14 B in samples A, B, and C are 21.9, 17.5, and 16.8 nm, respectively, and those of a-Fe are 18.7, 16.4, and 15.3 nm, respectively.…”

High and Ultra-High Coercive Materials in Spring-Exchange Systems—Review, Simulations and Perspective

“…There are real spring-exchange magnets such as sintered powder composites [ 39 , 40 , 41 ], core-shell nanoparticles [ 42 ], and multi-layer systems [ 43 , 44 ] that are known in the literature. In all cases, the expected decrease in coercivity with an increase in soft component was observed.…”

“…In all cases, the expected decrease in coercivity with an increase in soft component was observed. However, the spring-exchange mechanism allowed for enhancing the | BH | max parameter by 80% for FePt-Co core-shell nanoparticles [ 42 ], 30% for a SmCo-Co thin layer system [ 44 ], and 25% for a α-FeCo/Pr 2 Fe 14 B nanocomposite [ 39 ]. Moreover, progress has been reported for hard–soft ferrite systems, with the | BH | max reaching a value of nearly 30 kJ/m 3 [ 40 ].…”

Preparation and properties of nanoparticles by chemical reactions with assistance of physics factors

“…Nanoparticles may be the most studied In contrast to many complicated and expensive physical routes such as meltspinning [1][2][3], evaporation [4], sputtering [5], deformation [6], and solid state reactions [7], aqueous chemical techniques are simple and inexpensive for making nanoparticles [8,9].…”