New RFe12−Ta compounds and their related hydrides and carbides (R=Tb to Lu, 0.5≤x≤0.7)

57Fe Mössbauer and magnetic studies of DyFe12−x Ta x compounds

“…The data were refined by Rietveld analysis using the FULLPROF program. As shown in Figure 1, the lattice parameters increase slightly with increasing Ta content, consistent with the larger radius of Ta compared with Fe and similar to the behaviour of HoFe 12jx Ta x [4]. We also find that the Ta atoms occupy only the 8i sites in all of the compounds; this can be understood in terms of enthalpy effects and metallic radii as for the RFe 12jx Nb x system [6].…”

“…Analysis of the X-ray diffraction patterns showed that all samples are essentially single phase and have the ThMn 12 -structure as expected; samples exhibited typically less than 4 wt.% of !-Fe and Fe 2 Ta as impurity phases, similar to earlier findings [2,4]. The data were refined by Rietveld analysis using the FULLPROF program.…”

“…Recently, Piquer et al [2,3] reported that the Ta-stabilized phase of RFe 11.5 Ta 0.5 only forms with the heavier rare-earth elements Tb, Dy, Ho, Er and Lu. Vert et al [4] found that pure singlephase samples do not form but that all samples included !-Fe and/or Fe 2 Ta as impurity phases and approximately single phase samples of RFe 12 j x Ta x were stabilised for x = 0.5-0.7 [4]. Later, the magnetic structure of ErFe 11.5 Ta 0.5 was determined by neutron powder diffraction measurements and a spin reorientation detected from easy axis to easy cone at T sr = 40 K [2,3] or 49 K [5] with decreasing temperature.…”

Exchange interactions and magneto-crystalline anisotropy in RFe12−M and parent interstitial compounds

“…The Wigner-Seitz cell volumes of the 3d sites are ranged as follows: V(8i) > V(8j) > V(8f) [1] and it is clear that the size of the M atom plays an important role in the stabilisation of the ThMn 12 type of structure [2]. On the other hand an excessive enhancement of the unit cell volume due to the stabilising element will make the RFe 12−x M x effectively stable only in a narrower range of x compositions with Ti, Nb and Ta (1.46 < R M < 1.47 Å) than with other M elements (1.27 < R M < 1.39 Å) [3][4][5][6][7]. Besides, concerning the nature of the 8f type occupation, the enthalpy effects reinforce the site preference due to the size effect.…”

Structural stability, site preference and lattice vibrations of RFe12−xTax (R = Tb, Dy, Ho)

“…The interest in having as small an amount as possible of the third element, critical for the stabilization of the iron-rich phase with ThMn 12 -type structure, lies in the avoidance of the severe decrease in the Curie temperature and iron magnetization when increasing the M metal concentration to the upper limit of its solubility range [5,6]. However, up to the present only a few RFe 12−x M x systems are known which comply with this requirement; they form for M = Ta (x ≈ 0.5-0.7) [7][8][9][10], Nb (x ≈ 0.6-0.7) [11][12][13][14][15][16], and W (x ≈ 0.7) [17]. Apparently, the compounds with the highest iron content form when M is a 4d or 5d element, and particularly, with rare earths from Tb to Ho.…”