High-Field Magnetization Behavior of Mn-Al-C Alloys (original) (raw)
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Spark plasma sintering of Mn–Al–C hard magnets
Journal of Physics: Condensed Matter, 2014
The aim of this work was to study the phase transformations on a Mn 54 Al 44 C 2 ribbon sample obtained by melt spinning. It is expected that the magnetic properties are enhanced for the thin (25m) ribbon samples due to the homogeneity, fine grain size, increased solubility and fine dispersion of precipitates, which are attributes of liquid quenching technology.
Phase Transformation and Magnetic Properties of Mn--Al--C Permanent Magnets
1983
Phase transformation, microstructure and magnetic properties were investigated for Cu-(11-14) mol%Mn-20 mol%Ga. The structures of the magnetic domains were also investigated by Lorentz microscopy and electron holography. Plate-like martensite phase(M , ordered hcp) was observed in as-quenched Cu-12 mol%Mn-20 mol%Ga. Phase transformation from M martensite to phase(hcp) occurred at around 540 K on heating. The phase decomposed into 00 (ordered hcp) and (bcc) phase at around 700 K, then became the single phase at around 840 K. By subsequent slow cooling, phase was observed at room temperature. The results obtained from Lorentz microscopy and electron holography revealed that the twin plates of M martensite and the magnetic domain have one-to-one correspondence, suggesting high magneto-crystalline anisotropy energy of the martensite phase. The saturation magnetization and the Curie temperature increased with Mn content.
Hard magnetic properties of melt-spun Mn-Al-C alloys
The European Physical Journal Conferences
Structural and magnetic characterization of Mnx-yAl100-x-yC2y (x = {50, 55}; y = {0, 1}) meltspun ribbons is reported. To obtain the metastable ferromagnetic τphase, rapidly solidified alloys were annealed either in a vacuum furnace at 823 K or directly in the vibrating sample magnetometer under applied magnetic field. Optimal magnetic properties were demonstrated by Mn54Al44C2 samples proved to be singlephase with a coercivity of 0.19 T measured in both cases. For this composition the structural ɛ→τ phase transformation has been magnetically detected at 786 K, Curie temperature of τphase (Tc = 592 K, Tp = 610 K) has been determined using mean field approximations in ferromagnetic and paramagnetic regions. Rietveld refinement of Xray diffraction spectra was employed to analyse the phase constitution of annealed alloys, lattice parameters as a function of chemical composition and mean grain size for the phases involved.
Journal of Magnetism and Magnetic Materials, 2019
The effect of hot deformation parameters on the magnetic properties of Mn51Al47C2 (at%) alloy was investigated. The hysteresis loops of cylindrical samples hot compressed to 50% of initial height at temperatures of 600 °C , 650 °C and 700 °C with strain rates 0.001 S-1 and 0.1 S-1 were obtained by means of vibrating sample magnetometer. In order to find the effect of strain on the magnetic properties, hot compressed samples to 30%, 45%, 60% and 75% in a specific temperature and strain rate were investigated. It was found that by increasing strain and strain rate, the coercivity increases and the highest coercivity gained at the temperature of 650 °C. Moreover, by further straining, the developed texture changed and higher remanent magnetization was obtained in axial direction for lower strains and in radial direction for higher strains.
Mechanical alloying and theoretical studies of MnAl(C) magnets
Journal of Magnetism and Magnetic Materials
Mn55Al45, Mn55Al44C1, Mn52.2Al45.8C2 and Mn54.2Al43.8C2 were synthesized by the mechanical alloying method. It was the first time that a high purity τ phase up to 99% of weight percentage was obtained in Mn54.2Al43.8C2, which gave the highest saturation magnetization Ms = 570 kAm-1 ever reported by mechanical alloying method up to date. The crystallite size of the τ phase of MnAl(C) alloy decreased with increasing carbon doping, varying from 79 to 159 nm. Additionally, the coercivity (Hc) was found to be inversely proportional to the crystallite size of τ phase. Effect of doping carbon and its position in the τ phase of MnAl(C) alloy were also investigated for the first time by first-principle calculations. It was found that by inserting carbon at the interstitial site in the tetragonal structure, a strong stabilization effect and an expansion of unit cell were observed, which are in good agreement with the experimental results. Moreover, our results indicate that carbon doping reduces the magnetic moment of Mn.
Magnetic properties of the non-oriented ε-phase in Mn–Al–C permanent magnet
Materials Chemistry and Physics, 1999
High magnetic ®eld measurements have been performed on the Mn±Al±C alloy in the temperature range 4.2±283 K in the applied ®eld up to 140 kOe. The obtained results reveal that the 4-phase of the Mn±Al±C alloy is antiferromagnetic with the Ne Âel temperature equal to 97 K. Moreover, the domain structure observations of this alloy con®rm that the 4-phase of the Mn±Al±C alloy is non-magnetic.
Effect of Carbon Addition on Magnetic Order in Mn-Al-C Alloys
IEEE Transactions on Magnetics
Obtaining 100% of metastable τ-phase (L10) in Mn-Al alloys needs addition of carbon and Mn in excess to stabilize the phase. The excess of Mn could lead to partial antiferromagnetic coupling, that would result in a reduction in magnetization, which is in agreement with the experimental results. To clarify this question, (Mn0.55Al0.45)100−xCx alloys, with x between 0 and 2, were rapidly quenched from the melt (by melt-spinning) and annealed at 550 • C. In the as-cast state, the sample is in the hexagonal paramagnetic ε-phase, and after annealing, the sample is in the tetragonal ferromagnetic τ-phase. Different routes for the addition of carbon were used. The structural properties were determined by neutron diffraction, and the magnetic properties by means of VSM measurements and neutron diffraction (ND).
Journal of Applied Physics, 1992
Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable τ (L10) phase formed directly from the melt. Complete solidification to τ phase was interrupted by the competitive evolution of an equilibrium ε phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic τ phase in a Mn0.55Al0.433C0.017 alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034 alloy), a transition in structure development occurred so that the samples exhibited γ2 phase formation as well as τ and ε phases. Both microstructural observations and x-ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable...