Preparation and Magnetic Properties of MnBi Alloy and its Hybridization with NdFeB

Abstract

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature (T c ) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio M r /M s > 0.8. The exchange coupling was high, and the coercivity i H c of the magnets was ~11-13 kOe. The maximum value of the energy product (BH) max was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

On the Balance between Magnetization and Coercivity of MnBi Green Powders and Magnets Prepared Thereof

“…It revealed that the realization of this balance is, in the case of MnBi bulk magnets, crucially required and contributes an important role in enhancing the energy product (BH)max of MnBi bulk magnets. It has been proved that to have this balance, the route of producing MnBi bulk magnets should be carefully controlled to i) prepare alloys with the spontaneous magnetization Ms higher 8 kG; ii) grind alloys into powders owning the relation iHc(in kOe) > Mr(in kG); iii) warrantee the high alignment degree  of the bulk magnet greater 50; iv) use the compaction pressure Popt around 1700 psi to reach the magnet mass density  around 8.5 g/cm 3 . These listed values are the guide ones for controlling the route of producing high-performance MnBi bulk magnets with (BH)max towards the theoretical limit.…”

“…All the ball mill were done by 6 mm hard steel balls with the weighing ratio of balls:powders of 10:1. The composition phases of alloys and ball-milling powders were carried out by using D8 advance Brucker X-ray diffractometer (XRD) with Cu-K radiation with the scattering angle 2 scan in the range from 20 to 80 degrees by the scanning step of 0.05° for 2 s. The phase composition were analyzed by means of Rietveld refinement of XRD patterns for all the obtained diffraction peaks by using the Crystal Impact -Software for Chemists and Material Scientists and, in some cases, by the method of the instant determination of MnBi LTP content presented in the previous work [3]. The morphology of powders was studied by using the Field Emission Scanning Electron Microscopy FESEM Hitachi S-4800.…”

“…into powders. The LTLEBM powder was embedded in an epoxy resin to create an isotropic bonded magnet with  = 6.8 g/cm 3 . This powder was also used to prepare the bulk magnet using the hot compaction method under 18kG aligning field with the pressure of 2200 psi.…”

Effects of compression on magnetic properties of MnBi prepared by liquid-phase sintering

“…One of the difficulties in synthesizing highperformance LTP-MnBi is caused by the dissociation of Mn because of the peritectic interaction between Mn and Bi as seen in the Mn-Bi phase diagram. The peritectic reaction results in the interruption of LTP-MnBi formation, and there will always be an excess of Bi upon this reaction [8]. There is an attempt to separate the excess Bi using a magnetic field.…”

Effect of Mn grinding time on structural, chemical, and magnetic properties of the Manganese Bismuth prepared by sintering in vacuum

“…The essential for getting different magnetic performances is the peritectic reaction during MnBi synthesis [6]. The MnBi can be prepared by various approaches, such as arc-melting [7], melt-spinning [8], chemical reaction [9], and sintering [4]. The sintering technique employs a diffusion process that can synthesize high-purity LTP-MnBi [10].…”