Orientation by solidification in a magnetic field A new process to texture SmCo compounds used as permanent magnets (original) (raw)
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Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound
Scientific Reports, 2015
Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology.
Materials Characterization, 2018
The present paper proposes a method of graded materials preparation under a low horizontal magnetic field during directional solidification. The external horizontal magnetic field was applied to the mushy zone of the directionally solidified Al-10 wt% Cu and Al-18 wt% Si samples, which was perpendicular to the growth direction. Experimental results demonstrate that the applied horizontal magnetic field produces a gradient size distribution of the primary α(Al) grains in Al-10 wt% Cu alloys and a gradient fraction distribution of primary Si particles in Al-18 wt% Si alloys. 3D numerical simulations indicate that the formation of graded structure should be attributed to the migration of primary phase driven by the thermoelectric magnetic force (TEMF). The formation of segregation channel should be attributed to the TEM convection (TEMC) in the mushy zone. Further, in situ synchrotron X-ray radiography observations of the initial transient of directional solidification show that the primary α(Al) phases were migrated approximately along the direction perpendicular to the magnetic field. These results suggest that the TEM effects can greatly change the growth of primary grains and the solidification structure, and the application of an external horizontal magnetic field would be beneficial to fabricate the graded material during directional solidification.
Structural and magnetic investigation of Co-rich Sm–Co unidirectionally solidified alloys
Journal of Alloys and Compounds, 2007
Sm(Co, Fe, Cu, Zr) z alloys, with various degrees of crystallographic and magnetic texture, were synthesized by a route based on floating zone melting and unidirectional solidification. The phase composition, the microstructure and magnetisation curves of these materials were investigated by scanning electron microscopy, X-ray diffraction and magnetisation measurements. The trials undertaken by systematically varying the process parameters (heating power, floating zone velocity) allowed us to determine for each particular start composition the solidification regimes which yield materials with 1:5-and/or 2:17-type phases, free of Co metal precipitates, as well as with the crystallographic c-axis, easy magnetisation direction, respectively, oriented parallel or perpendicular to the temperature gradient main direction. The effect of solutionizing and ageing treatments on the microstructure and magnetic properties of the textured alloys was also investigated.
Acta Materialia, 2014
Six alloys were directionally solidified at low growth speeds (1-5 lm s À1) under a weak transverse magnetic field (60.5 T). The results show that the application of a weak transverse magnetic field significantly modified the solidification structure. Indeed, it was found that, along with the refinement of cells/dendrites, the magnetic field caused the deformation of liquid-solid interfaces, extensive segregations (i.e., freckles and channels) in the mushy zone, and a change in the mushy zone length. Further, in situ monitoring of the initial transient of the directional solidification was carried out by means of synchrotron X-ray radiography. It was observed that dendrite fragments and equiaxed grains were moved approximately along the direction perpendicular to the magnetic field. This result shows that a thermoelectric magnetic force (TEMF) acted on the liquid or the solid during directional solidification under a weak magnetic field. The TEMF during directional solidification under a transverse magnetic field was investigated numerically. The results reveal that a unidirectional TEMF acted on the solid and induced thermoelectric magnetic convection (TEMC) in the liquid. Modification of the solidification structure under a weak magnetic field is attributed to TEMC-driven heat transfer and interdendritic solute transport and TEMF-driven motion of dendrite fragments.
High performance isotropic Sm–(Co,Fe)–C and Sm–(Co,Fe,Mn)–C magnets by melt spinning
Journal of Applied Physics, 2008
The magnetic properties and microstructure of melt-spun ribbons with a composition Sm x ͑Co 1−y M y ͒ 100−x−z C z for M = Fe or Fe+ Mn and x = 10-15, y = 0-0.375, and z =0-6 have been studied systematically. The results indicate a strong dependence of the microstructure on the addition of C. The grain size decreases from few 100 nm to below 20 nm with addition of C. On the other hand, addition of Fe and Mn modifies both the saturation magnetization and the magnetocrystalline anisotropy. The Mn addition results in a coercivity of 11.7 kOe for Sm 12 ͑Co 0.75 Fe 0.185 Mn 0.065 ͒ 86.5 C 1.5 ribbons spun at 40 m / s. The highest remanence of 102 emu/ g was obtained in Sm 12 ͑Co 0.75 Fe 0.25 ͒ 83.5 C 4.5 ribbons spun at 50 m / s. A ͑BH͒ max of 14.7 MGOe with a coercivity of 5.6 kOe was obtained in as spun Sm 13 ͑Co 0.75 Fe 0.25 ͒ 82.5 C 4.5 ribbons.
Textured Development of Feeble Magnetic Ceramics by Colloidal Processing Under High Magnetic Field
Journal of the Ceramic Society of Japan, 2005
The controlled development of texture is one of the ways for effectively improving physical and mechanical properties. In this review paper, we introduce a new processing of textured ceramics with a feeble magnetic sus ceptibility by slip casting in a high magnetic field and subsequent heating. As an example of feeble magnetic ceramics, we demonstrate the fabrication of textured alumina in details. The susceptibility of diamagnetic aalu mina is very small, but the orientation energy of the alumina particle by a high magnetic field becomes greater than the thermal energy. aAlumina with a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field, the energy of crystal anisotropy becomes comparable to or greater than the energy of thermal motion. The degree of orientation depends on the processing factors, such as heating temperature, particle size, applied magnetic field, concentration of the suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other noncubic ceramics, such as TiO 2 , ZnO, SnO, hydrooxy apatite (HAP), AlN, SiC, Si 3 N 4 , etc.
Determination of Texture Orientation Related Magnetic Properties of Nickel-Cobalt Films
Zeitschrift für Naturforschung A, 2010
The determination of texture effects in nickel-cobalt (Ni-Co) films with different thickness, which were obtained by electrodeposition, has been investigated by the measurement of hysteresis loops at different angles. Easy-axis distribution measurements were performed as a function of the squareness M p (β ) and the correlations were established among the different thicknesses. The composition of Ni-Co films was determined by energy dispersive X-ray spectroscopy. The structural analysis made by X-ray diffraction revealed that all films have a polycrystalline face-centered cubic structure but their texture degrees vary depending on the film thickness. The determination of the easy-axis orientation in 2-D films from the M p (β ) obtained by the hystersis loops was studied using Fourier series analyses. The coefficient A 0 have a value of less then unity while A 2 is inversely proportional to the width of the distribution function which may cause the change in the texture preferential orientations. Therefore, the differences observed in the magnetic easy-axis distributions were attributed to the changes in texture orientations caused by the compositional differences at different thicknesses of the polycrystalline films.