Magnetic properties of LaCo13-based systems

Abstract

Four polycomponent systems based on LaCo13 have been studied: La(Co1−xFex)13, La(Co1−xAlx)13, La(Co1−x−yFexAly)13, and La0.7Nd0.3(Co0.7Fe0.3)13. These 1:13 systems were studied because of their potential for permanent magnet fabrication. LaCo13 has a high 3d metal content, the highest for any known rare-earth intermetallic, a 13 kG saturation induction, and a high Tc (1318 K). Unfortunately, it is cubic and lacks anisotropy. The substituted systems were examined as a portion of a program to find LaCo13-based systems of applications significance. Replacement of Co in LaCo13 by Fe and/or Al leads to a rapid decline in Tc for all systems studied. Replacement of Co by Al results in a decline in moment, whereas replacement by Fe leads to a rise in moment to 2.39μB/3d atom for La(Co0.4Fe0.6)13, as compared to 2.46μB/3d atom for Fe0.7Co0.3. Analysis of the magnetic data shows that vacancies occur in both half-bands for LaCo13 (4.8 spin up and 3.24 spin down) but in only one half-band in La(Co1−xAlx)13 for x≥0.2. Nd in these systems carries a moment of 3μB, close to that of the free tripositive ion.

The effect of Co substitution of Si on the structural and microstructural properties of GdCo9+xSi4−x

“…Results suggest that the Si atoms strongly prefer to occupy the site 16l (2) . Attempts to distribute the Si and Co (2) randomly in the two equivalent crystallographic sites 16l (1) and 16l (2) yield bad reliability factors. Replacing Si by Co in the site 16l (2) introduces systematic changes in the relative atomic coordinates.…”

“…As shown in Fig. 4, it is clear that replacing Si by Co in the site 16l (2) has opposite effects on the lattice parameters, it increases a and decreases c. The value c/a decreases as the Si content decreases, indicating that Si stabilizes the bodycentered tetragonal structure in the ratio 1:13. Regarding the small difference in atomic radii of Si (1.15 Å ) and Co (1.16 Å ), the changes in the lattice parameters can not be attributed to this difference but may depend on the symmetry of electronic configuration in the local symmetry of the site 16l.…”

“…LaCo 13 has a very large magnetization (130 emu/g at 300 K) and high magnetic transition temperature (T c Z 1318 K) which are both attributed to the high cobalt content [1,2]. It is the only stable compound with cubic NaZn 13 -type structure in all binary rare earth transition metal systems.…”

“…At higher Si content 3.8%x%4.2, almost single phase samples are formed, where GdCo 9 Si 4 is a true ternary compound with a fully ordered distribution of Gd, Co, and Si atoms within the space group I 4/mcm. This means that GdCo 13Kx Si x system is ordered with Si totally occupying the site16l (2) at xZ4. When x!4, some Co atoms will share Si in that site.…”

“…Fig. 1 shows the tetragonal unit cell with a polyhedron around the 16l (2) position. In the present work we studied the effect of replacing Si by Co on the structure and microstructure properties for single phase samples of GdCo 9Cx Si 4Kx (xZ0, 0.2, 0.4).…”