Journal articles: '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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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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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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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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11

Khanduri, H., S. A. Khan, S. K. Srivastava, I. Sulania, M. Chandra, J. Link, R. Stern, and D. K. Avasthi. "Irradiation induced enhancement of ferromagnetic τ-phase in MnAl alloy thin films on Si substrate." Materials Research Express 6, no. 5 (February 1, 2019): 056405. http://dx.doi.org/10.1088/2053-1591/ab005a.

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12

Thongsamrit, Wannisa, Thanida Charoensuk, Panissa Saetang, Pongsakorn Jantaratana, Chesta Ruttanapun, and Chitnarong Sirisathitkul. "Effects of Carbon Doping and Annealing Temperature on Magnetic MnAl Powders and MnAl Polymeric Composites." Applied Sciences 11, no. 5 (February 26, 2021): 2067. http://dx.doi.org/10.3390/app11052067.

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Process parameters leading to magnetic polymer composites, an essential ingredient in the additive manufacturing of rare-earth-free magnets, are investigated. The induction melting of manganese (Mn) and aluminum (Al), and subsequent annealing at 450, 500, or 550 °C for 20 min, gave rise to ferromagnetic τ–MnAl phase, as well as other phases. The nonmagnetic Al4C3 and oxide phases were then removed by the magnetic separation. Magnetic powders from the magnetic separation were incorporated in polylactic acid (PLA) matrix via a solution route. The remanent magnetization as high as 4.3 emu/g in the powder form was reduced to 2.3–2.6 emu/g in the composites. The reduction in coercivity was minimal, and the largest value of 814 Oe was obtained when the powder annealed at 450 °C was loaded in the composite. The phase composition and hence magnetic properties were even more sensitive to the carbon (C) doping. Interestingly, the addition of 3% C led to coercivity as high as 1445 Oe in MnAl–C powders without further annealing. The enhanced coercivity was attributed to the domain wall pinning by the AlMn3C phase, and magnetizations are likely increased by this phase.

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13

Xiang, Zhen, Yiming Song, Baiwen Deng, Erbiao Cui, Lunzhou Yu, and Wei Lu. "Enhanced formation and improved thermal stability of ferromagnetic τ phase in nanocrystalline Mn55Al45 alloys by Co addition." Journal of Alloys and Compounds 783 (April 2019): 416–22. http://dx.doi.org/10.1016/j.jallcom.2018.12.350.

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14

Palanisamy, Dhanalakshmi, Shailesh Singh, Chandan Srivastava, Giridhar Madras, and Kamanio Chattopadhyay. "Predicting Pathways for Synthesis of Ferromagnetic τ Phase in Binary Heusler Alloy Al-55 pct Mn Through Understanding of the Kinetics of ε–τ Transformation." Metallurgical and Materials Transactions A 47, no. 12 (September 13, 2016): 6555–68. http://dx.doi.org/10.1007/s11661-016-3756-4.

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15

Kim, Y. J., and J. H. Perepezko. "Formation of a metastable ferromagnetic τ phase during containerless melt processing and rapid quenching in Mn‐Al‐C alloys." Journal of Applied Physics 71, no. 2 (January 15, 1992): 676–80. http://dx.doi.org/10.1063/1.351326.

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16

Huang, J. H., and P. C. Kuo. "Effect of quenching temperature on the formation and magnetic properties of the ferromagnetic τ-phase in MnAlC alloys." Materials Science and Engineering: B 20, no. 3 (July 1993): 292–97. http://dx.doi.org/10.1016/0921-5107(93)90242-f.

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17

BEHERA, LAXMIDHAR, and FRANK SCHWEITZER. "ON SPATIAL CONSENSUS FORMATION: IS THE SZNAJD MODEL DIFFERENT FROM A VOTER MODEL?" International Journal of Modern Physics C 14, no. 10 (December 2003): 1331–54. http://dx.doi.org/10.1142/s0129183103005467.

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In this paper, we investigate the so-called "Sznajd Model" (SM) in one dimension, which is a simple cellular automata approach to consensus formation among two opposite opinions (described by spin up or down). To elucidate the SM dynamics, we first provide results of computer simulations for the spatio-temporal evolution of the opinion distribution L(t), the evolution of magnetization m(t), the distribution of decision times P(τ) and relaxation times P(μ). In the main part of the paper, it is shown that the SM can be completely reformulated in terms of a linear voter model (VM), where the transition rates towards a given opinion are directly proportional to frequency of the respective opinion of the second-nearest neighbors (no matter what the nearest neighbors are). So, the SM dynamics can be reduced to one rule, "Just follow your second-nearest neighbor". The equivalence is demonstrated by extensive computer simulations that show the same behavior between SM and VM in terms of L(t), m(t), P(τ), P(μ), and the final attractor statistics. The reformulation of the SM in terms of a VM involves a new parameter σ, to bias between anti- and ferromagnetic decisions in the case of frustration. We show that σ plays a crucial role in explaining the phase transition observed in SM. We further explore the role of synchronous versus asynchronous update rules on the intermediate dynamics and the final attractors. As compared to the original SM, we find three additional attractors, two of them related to an asymmetric coexistence between the opposite opinions.

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18

KOMORI, TATSUO, and HAJIME TAKAYAMA. "SLOW DYNAMICS IN THE 'GRIFFITHS PHASE' OF THE 3D ± J ISING SPIN GLASS." International Journal of Modern Physics C 07, no. 03 (June 1996): 371–78. http://dx.doi.org/10.1142/s0129183196000314.

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Slow dynamics in the 'Griffiths phase' of the 3D ± J Ising spin glass is studied by means of Monte Carlo simulation, in which the spectra of (logarithms of) relaxation times, P (x) with x = ln τ, are analyzed in detail. At each temperature P (x) exhibits a characteristic crossover behavior at around a certain value xc which in turn tends to diverge toward the spin-glass critical temperature Tc. The contributions to the branch x ≲ xc are interpreted due to the ordinary critical slowing down process associated with Tc (critical dynamics). The behavior of P (x) at x ≲ xc, on the other hand, is consistent with the picture of relaxation processes of large, rare clusters which are related to the Griffiths singularity at the Curie temperature of the corresponding pure ferromagnet (cluster dynamics).

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19

Ma, Xiaobai, Wenyun Yang, Hui Zhao, Shuai Yang, Chao Yun, Zhaochu Luo, Shunquan Liu, et al. "Giant exchange bias in the nanostructured MnAl thin ribbons." Applied Physics Letters 123, no. 1 (July 3, 2023). http://dx.doi.org/10.1063/5.0147078.

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In this study, Mn54Al46 thin ribbons composed of nanostructured ferromagnetic and antiferromagnetic phases were fabricated by a melt spinning method, and a tunable exchange bias field was obtained by precisely controlling the wheel speed and the cooling field. The x-ray diffraction result confirms the existence of the nanostructured Mn-poor ε phase. The pinned ferromagnetic Mn-poor ε phase coupled with the antiferromagnetic Mn-rich ε phase accounts for the exchange bias observed in the sample fabricated at a wheel speed of 65 m/s in which almost no τ phase is formed. Furthermore, the exchange bias field first increases and reaches the most significant reported value of 41 kOe in this system and then decreases with the increase in the cooling field, exhibiting an inversely proportional relationship with the magnetization. The decrease in the exchange bias field is believed to be related to the increased coupling thickness of the ferromagnetic phases with the increase in the cooling field.

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20

Jürries, Florian, Lukas Beyer, Kornelius Nielsch, and Thomas George Woodcock. "Targeted hydrolysis and decrepitation of Mn₃AlC precipitates: a route to a novel precursor of rare earth free MnAl-C permanent magnets." Journal of Physics D: Applied Physics, July 10, 2023. http://dx.doi.org/10.1088/1361-6463/ace5b9.

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Abstract In this work, Mn-Al-C alloys consisting of ε-MnAl and carbides of the types Mn3AlC and Al4C3 were produced and exposed to water at 80°C for 35 days. This led to the hydrolysis and decrepitation of the carbides and ultimately, of the material. The hydrolysis behaviour was studied by combined mass spectrometry, thermogravimetry and differential scanning calorimetry. Microstructural studies with scanning electron microscopy and x-ray diffraction were carried out. X-ray computed tomography was used to study the evolution of cracks on a macroscopic scale. As the Mn3AlC precipitates were present as parallel platelets inside the ε-grains, the hydrolysis resulted in parallel voids separating regions of ε with the same orientation. This ε-skeleton could be easily milled into ε flakes, which could be mechanically aligned so that their <001> directions were parallel. The ε powder was transformed into the ferromagnetic τ phase via heat treatment and is therefore suitable as a novel precursor material for the production of anisotropic τ-MnAl-C-based permanent magnets. Employing such a textured, ε-phase, precursor powder in an extrusion process could result in increased texture quality of the τ-phase with correspondingly enhanced magnetic properties.

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21

Rosier, T. M., Y. He, and N. A. El-Masry. "Microstructural and Magnetotransport (EHE) Properties of Epitaxial τ-MnAl on (100)GaAs Substrates by Pulsed Laser Deposition." MRS Proceedings 403 (1995). http://dx.doi.org/10.1557/proc-403-695.

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AbstractWe report on the crystal quality and magnetotransport properties (EHE) of epitaxial (001) τ-MnA1/GaAs(100) grown by the laser ablation deposition technique. Films (10–30 nm thick) were grown by two methods: (1) ablating a τ-MnAl target, prepared in-house; (2) alternate deposition of ultra thin layers of Mn and Al (˜6 periods) followed by annealing at different temperatures. For both deposition approaches ultrathin coherent epitaxial τ-MnAl films have been grown at temperatures in the range 250–420°C that is below the ε-phase transformation temperature. Reflection high energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HRTEM) were used to characterize the crystalline quality of the deposited films. The Extraordinary Hall Effect measurements (EHE) indicate that the deposited films are perpendicularly magnetized showing coercivity up to 6 kOe at room temperature. The epitaxial growth of thin film ferromagnetic materials on lattice matching semiconductor substrates offers the possibility of integrating magnetic and semiconducting devices.

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22

Sorescu, Monica, S. A. Schafer, and E. T. Knobbe. "Synthesis of Magnetite Particles by Pulsed Alexandrite Laser Processing of Metallic Glass Precursors." MRS Proceedings 397 (1995). http://dx.doi.org/10.1557/proc-397-393.

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ABSTRACTSamples of Fe78B13Si9 and Fe81B13.5Si3.5C2 metallic glasses were irradiated with a pulsed alexandrite laser (λ=750 nm, τ=60 μs) using different laser fluences. Kinetics of laser-induced phase transformations and fluence dependence of magnetic properties were studied by scanning electron microscopy (SEM) and Mössbauer spectroscopy. Low laser fluences were found to induce changes in magnetic texture and onset of crystallization. High laser fluences, however, correlated with additional oxidation effects and the formation of stoichiometric Fe3O4 particles in the irradiated alloy system. An activation energy of 11.9 eV was estimated for the laser-driven synthesis of magnetite nanoparticles. Pulsed alexandrite laser processing is an intriguing alternative technique for the controlled synthesis of iron oxide phases from ferromagnetic glass precursors.

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23

Shtender, Vitalii, Henry Stopfel, Daniel Hedlund, Dennis Karlsson, Rajasekhar Pothala, Björn Skårman, Fredrik Olsson, et al. "Influence of nano-VC on the structural and magnetic properties of MnAlC-alloy." Scientific Reports 11, no. 1 (July 14, 2021). http://dx.doi.org/10.1038/s41598-021-93395-2.

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AbstractAlloys of Mn55Al45C2 with additions of VC nano-particles have been synthesized and their properties evaluated. The Mn55Al45C2(VC)x (x = 0.25, 0.5 and 1) alloys have been prepared by induction melting resulting in a high content of the ferromagnetic τ-phase (> 94 wt.%). Powder X-ray diffraction indicates that nano-VC can be dissolved in the alloy matrix up to 1 at.%. On the other side, metallography investigations by scanning electron microscopy and scanning transmission electron microscope show inclusions of the nanosized additives in the microstructure. The effect of nano-VC on the grain and twin boundaries has been studied by electron backscattering diffraction. The magnetization has been measured by magnetometry up to 9 T while the domain structure has been studied using both magnetic force microscopy as well as Kerr-microscopy. For nano-VC contents above 0.25 at.%, a clear increase of the coercive force is observed, from 57 to 71 kA/m. The optimum appears to be for 0.5 at.% nano-VC which shows a 25% increase in coercive force without losing any saturation magnetization. This independent increase in coercivity is believed to originate from the nano-VC reducing the overall magnetic domain size. Overall, we observe that addition of nano-VC could be an interesting route to increase the coercive force of MnAl, without sacrificing saturation magnetization.

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Journal articles on the topic 'Ferromagnetic τ Phase'

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