Effect of Sm content on energy product of rapidly quenched and oriented SmCo5 ribbons

The Sm-content dependence of phase composition, anisotropy, and other magnetic properties of Sm1+δCo5 (δ ≤ 0.12) ribbons melt spun at 10 m/s has been studied. The samples consist of hexagonal SmCo5 grains whose c axes are preferentially aligned along the long direction of the ribbon. The lattice parameter a and the cell volume (V) increase with increasing Sm content δ, whereas c decreases. Sm addition appears to improve the degree of the preferred orientation of the c-axis and to increase the mean grain size, which weakens the effective intergranular exchange coupling. Therefore, the remanence ratio, coercivity, and squareness of the hysteresis loops are significantly enhanced. The remanence ratio of 0.91 and the maximum energy product of 21.2 MGOe, which is the highest value reported so far for Sm–Co ribbons, are achieved for δ = 0.06. High performance in combination with simple processing may facilitate high-temperature applications for anisotropic Sm1+δCo5 ribbons

Effect of Sm content on energy product of rapidly quenched and oriented SmCo5 ribbons

The Sm-content dependence of phase composition, anisotropy, and other magnetic properties of Sm1+δCo5 (δ ≤ 0.12) ribbons melt spun at 10 m/s has been studied. The samples consist of hexagonal SmCo5 grains whose c axes are preferentially aligned along the long direction of the ribbon. The lattice parameter a and the cell volume (V) increase with increasing Sm content δ, whereas c decreases. Sm addition appears to improve the degree of the preferred orientation of the c-axis and to increase the mean grain size, which weakens the effective intergranular exchange coupling. Therefore, the remanence ratio, coercivity, and squareness of the hysteresis loops are significantly enhanced. The remanence ratio of 0.91 and the maximum energy product of 21.2 MGOe, which is the highest value reported so far for Sm–Co ribbons, are achieved for δ = 0.06. High performance in combination with simple processing may facilitate high-temperature applications for anisotropic Sm1+δCo5 ribbons

A TEM study of Fe\u3csub\u3e3+x\u3c/sub\u3e Co\u3csub\u3e3-x\u3c/sub\u3eTi\u3csub\u3e2\u3c/sub\u3e (x = 0, 1, 2, 3) intermetallic alloys

A TEM study has been carried out on crystal structures in the rare-earth-free intermetallic alloys, Fe3+xCo3-xTi2 (x = 0, 1, 2, 3). These alloys have been demonstrated to have potentially high magnetic anisotropy. In these alloys, the main intermetallic compound was recently reported as a new hexagonal phase with a space group of P-6 m2. The present study reveals that the main compound belongs to Laves C14 variant surrounded by α-Fe type crystal as secondary phase in the Fe3+xCo3-xTi2 (x = 0, 1, 2, 3) alloys, in agreement with the Fe-Ti and Fe-Co-Ti phase diagrams. The SAED, EDS, HRTEM and XRD techniques have been carried out to characterize the intermetallic compounds in the Fe3+xCo3-xTi2 (x = 0, 1, 2, 3) alloys

New Heusler compounds in Ni-Mn-In and Ni-Mn-Sn alloys

Rapidly quenched ternary Ni-Mn-T (T = In, Sn) alloys exhibit features associated with magnetic skyrmions, so that XRD, TEM, EDS, SAED and HREM investigations were carried out for structural characterization on the two alloy systems. In this paper, we report a new type of Mn-rich Heusler compound with a cubic unit cell, a = 0.9150 nm in Ni-Mn-In and a = 0.9051 nm in Ni-Mn-Sn, which coexist with a Ni-rich full-Heusler compound with defects, a = 0.6094 nm in Ni-Mn-In and a = 0.6034 nm in Ni-Mn-Sn. A further analysis of the experimental results reveals a close structural relationship between these two compounds

Synthesis and magnetism of single-phase Mn-Ga films

Single-phase noncubic Mn-Ga films with a thickness of about 200 nm were fabricated by an in situ annealing of [Mn(x)/Ga(y)/Mn(x)]5 multilayers deposited by e-beam evaporation. Mn-Ga alloys prepared in three different compositions Mn2Ga5 and Mn2Ga were found to crystallize in the tetragonal tP14 and tP2 structures, respectively. Mn3Ga crystallizes in the hexagonal hp8 or tetragonal tI8 structures. All three alloys show substantial magnetocrystalline anisotropy between 7 and 10 Mergs/cm3. The samples show hard magnetic properties including coercivities of Mn2Ga5 and Mn2Ga about 12.0 kOe and of Mn3Ga about 13.4 kOe. The saturation magnetization and Curie temperature of Mn2Ga5, Mn2Ga, and Mn3Ga are 183 emu/cm3 and 435 K, 342 emu/cm3 and 697 K, and 151 emu/cm3 and 798 K, respectively. The samples show metallic electron transport up to room temperature

Effect of boron doping on nanostructure and magnetism of rapidly quenched Zr\u3csub\u3e2\u3c/sub\u3eCo\u3csub\u3e11\u3c/sub\u3e-based alloys

The role of B on the microstructure and magnetism of Zr16Co82.5-xMo1.5Bx ribbons prepared by arc melting and melt spinning is investigated. Microstructure analysis show that the ribbons consist of a hard-magnetic rhombohedral Zr2Co11 phase and a minor amount of soft-magnetic Co. We show that the addition of B increases the amount of hard-magnetic phase, reduces the amount of soft-magnetic Co and coarsens the grain size from about 35 nm to 110 nm. There is a monotonic increase in the volume of the rhombohedral Zr2Co11 unit cell with increasing B concentration. This is consistent with a previous theoretical prediction that B may occupy a special type of large interstitial sites, called interruption sites. The optimum magnetic properties, obtained for x = 1, are a saturation magnetization of 7.8 kG, a coercivity of 5.4 kOe, and a maximum energy product of 4.1 MGOe

Novel Polyethylene Fibers of Very High Thermal Conductivity Enabled by Amorphous Restructuring

High-thermal-conductivity polymers are very sought after for applications in various thermal management systems. Although improving crystallinity is a common way for increasing the thermal conductivity (k) of polymers, it has very limited capacity when the crystallinity is already high. In this work, by heat-stretching a highly crystalline microfiber, a significant k enhancement is observed. More interestingly, it coincides with a reduction in crystallinity. The sample is a Spectra S-900 ultrahigh-molecular-weight polyethylene (UHMW-PE) microfiber of 92% crystallinity and high degree of orientation. The optimum stretching condition is 131.5 °C, with a strain rate of 0.0129 s−1 to a low strain ratio (∼6.6) followed by air quenching. The k enhancement is from 21 to 51 W/(m·K), the highest value for UHMW-PE microfibers reported to date. X-ray diffraction study finds that the crystallinity reduces to 83% after stretching, whereas the crystallite size and crystallite orientation are not changed. Cryogenic thermal characterization shows a reduced level of phonon-defect scattering near 30 K. Polarization Raman spectroscopy finds enhanced alignment of amorphous chains, which could be the main reason for the k enhancement. A possible relocation of amorphous phase is also discussed and indirectly supported by a bending test. 3 supplemental files are attached below

Magnetism and electron transport of MnyGa (1 \u3c y \u3c 2) nanostructures

Nanostructured MnyGa ribbons with varying Mn concentrations including Mn1.2Ga, Mn1.4Ga, Mn1.6Ga, and Mn1.9Ga were prepared using arc-melting and melt-spinning followed by a heat treatment. Our experimental investigation of the nanostructured ribbons shows that the material with y = 1.2, 1.4, and 1.6 prefers the tetragonal L10 structure and that with y = 1.9 prefers the D022 structure. We have found a maximum saturation magnetization of 621 emu/cm3 in Mn1.2Ga which decreases monotonically to 300 emu/cm3 as y reaches 1.9. Although both the L10- and D022-MnyGa samples show a high Curie temperature (Tc) well above room temperature, the value of Tc decreases almost linearly from 702K for Mn1.9Ga to 551K for Mn1.2Ga. All the ribbons are metallic between 2K and 300K but the Mn1.2Ga also shows a resistance minimum near 15K. The observed magnetic properties of the MnyGa ribbons are consistent with the competing ferromagnetic coupling between Mn moments in the regular L10-MnGa lattice sites and antiferromagnetic coupling with excess Mn moments occupying Ga sites

Localization effects and Anomalous Hall conductivity in a disordered 3D ferromagnet

We have prepared the Heusler alloy CoFeV0.5Mn0.5Si in bulk form via arc melting. CoFeV0.5Mn0.5Si is ferromagnetic with a Curie temperature of 657 K. The longitudinal resistivity exhibits a minimum at 150 K, which is attributable to competition between quantum interference corrections at low temperatures and inelastic scattering at higher temperatures. The magnetoresistance (MR) is positive and nearly linear at low temperatures and becomes negative at temperatures close to room temperature. The positive MR in the quantum correction regime is evidence of the presence of the enhanced electron interaction as a contributor to the longitudinal resistivity. Hall effect measurements indicate a carrier concentration of the order of 1022 cm-3, which is nearly 3 orders of magnitude higher than that found in the “parent” material CoFeMnSi. The higher carrier concentration is consistent with the predicted half metallicity of CoFeV0.5Mn0.5Si. The anomalous Hall conductivity of CoFeV0.5Mn0.5Si is temperature independent for temperatures below the resistivity minimum, which is strong evidence of the absence of quantum interference effects on the anomalous Hall conductivity in a 3D ferromagnet

Unusual perpendicular anisotropy in Co\u3csub\u3e2\u3c/sub\u3eTiSi films

Thin films of Co2TiSi on MgO are investigated experimentally and theoretically. The films were produced by magnetron sputtering on MgO(001) and have a thickness of about 100 nm. As bulk Co2TiSi, they crystallize in the normal cubic Heusler (L21) structure, but the films are slightly distorted (c/a = 1.0014) and contain some antisite disorder. The films exhibit a robust perpendicular anisotropy of 0.5 MJ m−3. This result is surprising for several reasons. First, surface and interface anisotropies are too small to explain perpendicular anisotropy in such rather thick films. Second, Co2TiSi has a substantial magnetization and crystallizes in a cubic Heusler structure, so that conventional wisdom predicts a preferential magnetization direction in the film plane rather than perpendicular. Third, the lattice strain of 0.14% is unable to account for the perpendicular anisotropy. We explain the perpendicular anisotropy as a quasicubic symmetry breaking chemical-ordering effect promoted by the substrate