Academic literature on the topic 'Ferromagnetic τ Phase'

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Journal articles on the topic "Ferromagnetic τ Phase"

1

Palmer, Shane, John Martin, Paul Lindquist, and Peter Müllner. "Transformation Pathways of Ferromagnetic Mn-Al-Ga-Ni." Magnetochemistry 9, no. 5 (May 11, 2023): 128. http://dx.doi.org/10.3390/magnetochemistry9050128.

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This study investigates the impact of alloying Mn-Al-Ga with 3 at.-% Ni and the stability and formation mechanisms of the τ phase and the resulting magnetic properties. The stabilizing effect of Ga on the τ phase was verified, and the ternary alloy’s magnetization was measured up to M2T=482kA/m−1. The phase transformation from γ2 to τ in ternary Mn-Al-Ga was demonstrated microscopically. The solubility limit of Ni into the τ phase was exceeded at 3 at.-% and a primitive cubic κ phase formed. The Ni addition stabilized the τ phase. The highest magnetization at 2 T for the Mn52Al39.4Ga5.6Ni3 alloy was M2T=416kA/m−1 . A new transformation pathway was demonstrated by first annealing the Mn-Al-Ga-Ni alloy at 800 °C for 24 h, which forms a nearly single κ phase, which is followed by a second anneal at 500 °C for 24 h at which the phase τ formed with some remaining κ phase. This is a new transformation mechanism since it involves a phase reaction from κ to τ. The energy product of the Mn-Al-Ga-Ni alloy exceeded that of the ternary Mn-Al-Ga alloy by a factor of 4.5. The κ-phase particles in the Mn-Al-Ga-Ni alloy hinder magnetic domain boundary motion, thus providing a method for magnetic hardening and increasing the energy product.
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2

Yanar, C., J. M. K. Wiezorek, V. Radmilovic, and W. A. Soffa. "Characterization of Interphase Interfaces Developed During the Ordering Transformation (ε (A3) →τ (L10)) In Manganese-Aluminum Alloys." Microscopy and Microanalysis 6, S2 (August 2000): 364–65. http://dx.doi.org/10.1017/s1431927600034310.

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Alloys based on the ferromagnetic τ-phase, which may be established in the Mn-Al system for near equiatomic composition [1], exhibit high magnetocrystalline anisotropy and coercivity and are of interest for advanced permanent magnet applications [2], Their technologically important properties depend strongly on the microstructure and defect structure development associated with the transformation from the disordered hexagonal (A3) ε-phase to the ordered tetragonal (L10) τ-phase. The structure, morphology and chemistry of the (ε/τ) interphase interfaces have been studied by methods of optical and electron microscopy (OM, SEM and TEM) in order to determine the nature of this technically important and scientifically interesting phase transformation. The optimization of processing-property relationships for this class of ferromagnetic materials requires a detailed understanding of the mechanisms facilitating the ordering process.The τ-phase nucleates at prior ε-grain boundaries (ε-GB) and exhibits a serrated, faceted growth morphology (FIG. l).
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3

Pacheco, Victor, Björn Skårman, Fredrik Olsson, Dennis Karlsson, Hilmar Vidarsson, and Martin Sahlberg. "Additive Manufacturing of MnAl(C)-Magnets." Alloys 2, no. 2 (May 15, 2023): 100–109. http://dx.doi.org/10.3390/alloys2020007.

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Permanent magnets are becoming more and more relevant for modern society. As the most widely used permanent magnets contain rare-earth elements, the increased dependence on these strategic elements is worrisome, and the pursuit for rare-earth free alternatives has become a strategic goal in many countries. The metastable and ferromagnetic τ-phase that forms in the MnAl(C) system is one of the most promising alternatives, and since its discovery, major efforts have been made to improve its performance and realize its full potential. One major factor that has prevented a widespread commercialization of MnAl(C) permanent magnets is their relatively low coercivity. Here, we demonstrate that additive manufacturing, using laser powder bed fusion, can be used to produce MnAl in its high-temperature polymorph (ε, hcp), which can be subsequently transformed, through post-heat treatments to the ferromagnetic τ-phase. Although we successfully obtained a preferential orientation of the ε-phase with <001> parallel to the build direction, this did not translate into a strong preferential orientation in the τ-phase, thus indicating that the phase transformation occurs by the migration of incoherent interfaces. The MnAl(C) samples are characterized by a density of ≈4.4 g/cm3, a saturation magnetization of 39.3 Am2/kg, a coercivity of 168 kA/m, and a remanence of 17.5 Am2/kg.
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4

Morisako, A., M. Matsumoto, and M. Naoe. "Synthesis of ferromagnetic τ phase of Mn‐Al films by sputtering." Journal of Applied Physics 61, no. 8 (April 15, 1987): 4281–83. http://dx.doi.org/10.1063/1.338445.

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5

Maccari, F., A. Aubert, S. Ener, E. Bruder, I. Radulov, K. Skokov, and O. Gutfleisch. "Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering." Journal of Materials Science 57, no. 10 (March 2022): 6056–65. http://dx.doi.org/10.1007/s10853-022-07002-4.

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Abstract Mn–Al–C is intended to be one of the “gap magnets” with magnetic performance in-between ferrites and Nd-Fe-B. These magnets are based on the metastable ferromagnetic $$\tau$$ τ -phase with L1$$_0$$ 0 structure, which requires well controlled synthesis to prevent the formation of secondary phases, detrimental for magnetic properties. Here, we investigate the formation of $$\tau$$ τ -phase in Mn–Al–C using Spark Plasma Sintering (SPS) and compare with conventional annealing. The effect of SPS parameters (pressure and electric current) on the phase formation is also studied. Single $$\tau$$ τ -phase is obtained for annealing 5 min at $$500~^\circ \hbox {C}$$ 500 ∘ C with SPS. In addition, we show that the initial grain size of the $$\epsilon$$ ϵ -phase is influencing the $$\tau$$ τ -phase transformation and fraction at a given annealing condition, independently of the annealing method used. A faster transformation was observed for smaller initial $$\epsilon$$ ϵ -grains. The samples obtained by SPS showed comparable magnetic properties with the conventional annealed ones, reaching coercivity of 0.18 T and saturation magnetization of 114 Am$$^2$$ 2 /kg in the optimized samples. The similarity in coercivity is related to the microstructure, as we reveal the presence of structure defects like twin boundaries and dislocations in both materials. Graphical abstract
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6

Kobayashi, Ryota, Yoshifuru Mitsui, Rie Y. Umetsu, Kohki Takahashi, Masaki Mizuguchi, and Keiichi Koyama. "Magnetic-Field-Induced Enhancement of Phase Transformation in Ferromagnetic τ-Mn-Al." Journal of the Japan Institute of Metals and Materials 83, no. 6 (June 1, 2019): 181–85. http://dx.doi.org/10.2320/jinstmet.j2018057.

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7

Ochando-Pulido, Javier Miguel, Gassan Hodaifa, María Dolores Víctor-Ortega, and Antonio Martínez-Ferez. "A Novel Photocatalyst with Ferromagnetic Core Used for the Treatment of Olive Oil Mill Effluents from Two-Phase Production Process." Scientific World Journal 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/196470.

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Photocatalytic degradation of olive oil mill wastewater from two-phase continuous centrifugation process was studied. A novel photocatalyst with ferromagnetic properties was characterized and investigated. The degradation capacity of the photocatalytic process of olive oil washing wastewater (OMW) and mixture of olives and olive oil (1 v/v) washing wastewaters (MOMW) was demonstrated. At lab-scale, the %COD removal and residence time (τ) for MOMW and OMW were 58.4% (τ=2 h) and 21.4% (τ=3 h), respectively. On the other hand, at pilot scale, 23.4%CODremoval, 19.2% totalphenolsremoval, and 28.1% total suspendedsolidsremovalwere registered at the end of the UV/TiO2process for OMW, whereas 58.3%CODremoval, 27.5% totalphenolsremoval, and 25.0% total suspendedsolidsremovalfor MOMW. Also, before the UV/TiO2reaction, a pH-T flocculation operation as pretreatment was realized. The overall efficiency of the treatment process for MOMW was up to 91% ofCODremoval, in contrast with 33.2% ofCODremovalfor OMW.
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8

Martínez-Sánchez, Hugo, Juan David Gámez, José Luis Valenzuela, Hernan Dario Colorado, Lorena Marín, Luis Alfredo Rodríguez, Etienne Snoeck, et al. "Optimized Route for the Fabrication of MnAlC Permanent Magnets by Arc Melting." Molecules 27, no. 23 (November 30, 2022): 8347. http://dx.doi.org/10.3390/molecules27238347.

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The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ-MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε-MnAlC ingot that completely transformed into τ-MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε-MnAlC alloy that is formed by two types of ε-phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ-MnAlC alloy exhibited a remanent magnetization of 42 Am2/kg, a coercive field of 0.2 T and a maximum energy product, (BH)max, of 6.07 kJ/m3, which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε-MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ-MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ-MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.
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9

Li, Pu, Jung Goo Lee, Xing Long Dong, and Chul Jin Choi. "Preparation and Characteristics of MnAlC Nanoparticles by Plasma Arc-Discharge." Materials Science Forum 675-677 (February 2011): 307–10. http://dx.doi.org/10.4028/www.scientific.net/msf.675-677.307.

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MnAlC nanoparticles were synthesized by plasma arc-discharge method. Heat treatment of these nanoparticles at temperature from 400 to 600 °C resulted in the formation of the ferromagnetic τ-phase. Most of the nanoparticles had nearly spherical shape, smooth surface and core/shell structure. The shells of the nanoparticles mainly consisted of Al2O3 and a small amount of Mn oxides. Though the saturation magnetization of MnAlC nanoparticles was lower than that of bulk samples due to the effect of nonmagnetic phases (β, γ2 and Mn3AlC) and the oxide shell, the highest coercivity, up to 5.6 kOe in the MnAlC magnets, was achieved when annealed at 500 °C for 30 min.
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10

Baruchel, J., C. Patterson, and J. P. Guigay. "Neutron diffraction investigation of the nuclear and magnetic extinction in MnP." Acta Crystallographica Section A Foundations of Crystallography 42, no. 1 (January 1, 1986): 47–55. http://dx.doi.org/10.1107/s0108767386099919.

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The absolute values of the reflecting powers ρ are measured for the 200 and 2 ± τ, 0, 0 set of magnetic and nuclear reflections in the helimagnetic phase of a good-quality crystal of MnP as a function of its thickness. Severe and very different extinction effects are observed for the magnetic and nuclear reflections (y magnetic ~ 0.4, y nuclear ~ 0.02 for the largest thickness). This corresponds to the spectacular result that the magnetic reflecting powers ρ ± are twice as big as the nuclear one ρN , in spite of the fact that the scattering cross sections |F ±|2 are about ten times smaller than the nuclear |FN |2. The nuclear results appear consistent with dynamical theory while the magnetic ones are not. They can be explained by Zachariasen's type II secondary extinction model based on the chirality domain pattern. The same measurements were performed in the ferromagnetic phase, yielding y ferro ≃ 0.03. A model using the relative sizes of the ferromagnetic and chirality domains is presented.
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