Calculation of magnetic anisotropy energy in SmCo5

SmCo5 is an important hard magnetic material, due to its large magnetic anisotropy energy (MAE). We have studied the magnetic properties of SmCo5 using density functional theory (DFT) calculations where the Sm f-bands, which are difficult to include in DFT calculations, have been treated within the LDA+U formalism. The large MAE comes mostly from the Sm f-shell anisotropy, stemming from an interplay between the crystal field and the spin-orbit coupling. We found that both are of similar strengths, unlike some other Sm compounds, leading to a partial quenching of the orbital moment (f-states cannot be described as either pure lattice harmonics or pure complex harmonics), an optimal situation for enhanced MAE. A smaller portion of the MAE can be associated with the Co-d band anisotropy, related to the peak in the density of states at the Fermi energy. Our result for the MAE of SmCo5, 21.6 meV/f.u., agrees reasonably with the experimental value of 13-16 meV/f.u., and the calculated magnetic moment (including the orbital component) of 9.4 mu_B agrees with the experimental value of 8.9 mu_B.Comment: Submitted to Phys. Rev.

Magnetic properties of nanostructured CoSm/FeCo films

Co80Sm29/Fe65Co35 bilayer and multilayer films with Cr underlayers and overlayers have been fabricated and studied. All the samples prepared have in-plane anisotropy and the hysteresis loops were simple single loops for tFeCo≤300 Å indicating that the two phases are strongly exchange coupled. The magnetization of these samples is found to increase with increasing FeCo layer thickness for a fixed CoSm layer thickness. The coercivity, anisotropy constant, and anisotropy field for films with fixed CoSm layer thickness were found to decrease with increasing FeCo layer thickness. The magnetization squareness values of the hysteresis loops in the direction parallel to the film plane, for different CoSm and FeCo layer thicknesses, were found to be close to S≊0.75. The energy products for these samples vary from about 6 MG Oe at room temperature to 26 MG Oe at 30 K. The shape and the behavior of the initial loops and the minor loops suggest that wall pinning is the dominant coercivity mechanism in these films. Reversible demagnetization curves were measured and found to be consistent with the behavior expected for ‘‘exchange-spring’’ magnets

The influence of TiO2 polymorph, mechanical milling and subsequent sintering on the formation of Ti-substituted spinel-related Li0.5Fe2.5O4

Single-phased spinel-related titanium-substituted Li0.5Fe2.5O4 has been synthesized by sintering in air a mechanically pre-milled mixture of lithium carbonate, corundum-related iron (III) oxide and the rutile polymorph of titanium (IV) oxide at 700 °C (12 h). This temperature is ca. 450–500 °C less than the temperatures at which the material is normally prepared by conventional ceramic techniques. On replacing the rutile polymorph of titanium (IV) oxide in the pre-milled mixture by the anatase form the formation of single-phased titanium-substituted Li0.5Fe2.5O4 was not achieved even after sintering the mixture at 1,000 °C (12 h)

Magnetic and structural properties of Sm\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e10\u3c/sub\u3eCo\u3csub\u3e7\u3c/sub\u3e/M\u3csub\u3ex\u3c/sub\u3eC\u3csub\u3ey\u3c/sub\u3e thin films

The structural and magnetic properties of Sm2Fe10Co7/MxCy (M=A1 and Si; x≥0 and y≥0) multilayer films with Ta underlayers and overlayers before and after annealing at 700 °C for 5-12 min have been fabricated and studied. Structural studies show evidence of layer diffusion upon annealing. X-ray diffraction shows that the samples after annealing consist of a soft phase, α -Fe, and a hard phase with the 2-17-type structure. The samples studied have in-plane anisotropy with single hysteresis loops indicating that the two phases are strongly exchange coupled. After annealing, the coercivity of samples with AlxCy is found to increase with increasing AlxCy composition to a maximum of 3.3 kOe. The energy products for these samples are found to increase from 1.4 MGOe for SmFeCo to 8 MGOe for SmFeCo with AlxCy

Magnetic and structural properties of SmCo\u3csub\u3e7-x\u3c/sub\u3eCu\u3csub\u3ex\u3c/sub\u3e alloys

We report the structural and magnetic properties of SmCo7-xCux, where x= 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7. X-ray diffraction shows that these alloys from the disordered hexagonal TbCu7-type structure. For large values of x (x≥0.8) the hexagonal TbCu7-type structure cannot be formed. X-ray diffraction on magnetically aligned samples show that these samples have uniaxial anisotropy. The lattice parameters (a and c) are dependent on the Cu concentration, and the unit cell volume is found to increase with x. The saturation magnetization decreases with x at both room temperature and 25 K. The Curie temperature increases with x for small values of x while it decreases with x for large values of x. A maximum value of Tc = 852 °C is found in these alloys

Mössbauer study of permanent-magnet materials: Sm\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e17-x\u3c/sub\u3eAl\u3csub\u3ex\u3c/sub\u3e compounds

The Fe57 Mössbauer spectra of Sm2Fe17-xAlx, where x=0, 1.0, 2.0, 3.0, and 4.0, have been measured at room temperature and analyzed. The ternary compounds Sm2Fe17-xAlx have the rhombohedral Th2Zn17 structure. Mössbauer measurements showed that all the compounds studied were ferromagnetic. The average hyperfine field was found to decrease with the increasing aluminum concentration, which is in qualitative agreement with magnetic measurements. The decrease in the average hyperfine field was from 224 kOe at x=0 to 174 kOe at x=4. By fitting the spectra we found that the hyperfine fields for the iron sites decrease in the order 6c, 9d, 18f, and 18h. The measured average isomer shift relative to α-iron was found to increase linearly with x. Analysis of the spectra showed that Al atoms occupy the 6c, 18h, and 18f, but not 9d, Fe sites and the fraction of occupancy of Al was found to depend on x

Structure and magnetic properties of SmCo\u3csub\u3e7-x\u3c/sub\u3eTi\u3csub\u3ex\u3c/sub\u3e with TbCu\u3csub\u3e7\u3c/sub\u3e-type structure

The SmCo7-xTix, x = 0–0.56 bulk samples are prepared by arc melting. X-ray diffraction indicates that samples with 0.2\u3cx7-type structure phase and other minor phases appear for other values of x, which indicates that Ti helps stabilize the 1-7 phase. The lattice parameters ratio (c/a) increases with increasing Ti concentration. Room temperature saturation magnetization and Curie temperature decrease with increasing x. X-ray diffraction and magnetization measurements on aligned samples show that all samples studied have uniaxial anisotropy. The anisotropy field is found to increase with increasing x reaching a maximum of 175 kOe at x = 0.28 and then decreases for higher values of x. This anisotropy field is 20% higher than that of the same compound with Th2Zn17-type structure

Mössbauer, magnetic, and electronic-structure studies of YFe\u3csub\u3e12-x\u3c/sub\u3eMo\u3csub\u3ex\u3c/sub\u3e compounds

Mössbauer spectra, magnetization measurements, and self-consistent spin-polarized electronic structures of YFe12-xMox, where x=0.5, 1.0, 2.0, 3.0, and 4.0, are reported. The ternary compounds YFe12-xMox have the crystalline tetragonal ThMn12 structure. Analyses of the Mössbauer spectra show that Mo atoms occupy the 8i Fe sites of the ThMn12 structure, in agreement with previous observations. Room-temperature magnetic and Mössbauer measurements show that the compounds with x≤2.0 are ferromagnetic and with x≥3.0 are paramagnetic. Measurements at 25 K show that all the samples are magnetically ordered. The magnetic hyperfine field is found to decrease with increasing Mo concentration, which is in qualitative agreement with the calculated magnetic moments. The calculated magnetization decreases less rapidly with increasing x than the experimental data. In general the data suggest that with increasing Mo concentration there is an increase of antiferromagnetic coupling among the Fe moments, which leads to cluster-glass or spin-glass-like phenomena. The measured isomer shift relative to α-iron is found to decrease linearly with x

High-temperature magnetic properties of mechanically alloyed SmCo \u3csub\u3e5\u3c/sub\u3e and YCo\u3csub\u3e5\u3c/sub\u3e magnets

The high-temperature coercivity of mechanically alloyed and subsequently annealed RCo5 (R=Sm and Y) is studied. The annealed materials have the hexagonal CaCu5 structure with 2 : 17 (or 1 : 7) regions as a minor phase. High-temperature magnetic measurements showthat the coercivities of materials decrease with increasing temperature fromroom-temperature to 873 K, but that the temperature coefficient of the coercivity of YCo5 is much smaller than that of SmCo5. This behavior is explained in terms of the intrinsic temperature variation of the magnetocrystalline anisotropy