Intrinsic and extrinsic magnetic properties of nanocrystalline Pr₂(Co,Fe)₇

Abstract

In this work, we present a study focused on the effect of partial substitution of Co by Fe on structure and magnetic properties of nanocrystalline Pr 2 Co 7 . These compounds were synthesized by mechanical alloying and to correlate their properties with microstructural evolution, a multi-scale study by: X-ray diffraction (XRD), transmission electron microscopy, and magnetization was carried out. The Rietveld analysis of XRD diagrams shows that Pr 2 Co 7Àx Fe x , annealed at 973 K, mainly adopt a hexagonal Ce 2 Ni 7 type structure with P6 3 /mmc space group. These pseudo-ternary compounds exhibit more interesting magnetic properties than the binary Pr 2 Co 7 compounds.A systematic study of the intrinsic magnetic properties of these alloys shows that the substitution leads to enhancement of the Curie temperatures (T C ) by 26% for a Fe content equal to 0.5. This increase is due to the electronic as well as the magnetovolume effects. In addition, the study of extrinsic magnetic properties of the Pr 2 Co 6.5 Fe 0.5 compound has revealed the existence of a large coercive field H c , and a high remanent magnetization M r . Our results show that in these alloys, iron in solid solution has a strong effect on hardness and ordering temperature, which is particularly promising for permanent magnet applications.

Electronic structure and magnetic properties of Pr–Co intermetallics:ab initioFP-LAPW calculations and correlation with experiments

“…It is worth noting that the intrinsic magnetic properties are highly dependent on the interatomic Co-Co distances in the interaction exchange [31,32]. The magnetization measurements M(T) are displayed in figure 3, and the related Curie temperature T C estimated from the minimum of ∂M ∂T is found to be equal to 600 K for the Pr 2 Co 7 hexagonal phase (2:7 H) and 580 K for the rhombohedral (2:7 R).…”

Influence of Chemical Substitution and Light Element Insertion on the Magnetic Properties of Nanocrystalline Pr2Co7 Compound

“…The second is a rhombohedral (2:7 R) structure of the Gd 2 Co 7 type (R 3m space group) that is stable at T a ≥ 1223 K. The lattice parameters are a = b = 5.068 Å and c = 36.549 Å Ṫhe Pr 2 Co 7 cells can be defined by stacking the hexagonal structural blocks for PrCo 5 (CaCu 5 -type structure) and the cubic PrCo 2 blocks (MgCu 2 -and MgZn 2 -type structures) along the common hexagonal (trigonal for PrCo 2 ) axis [54]. The lattice parameters of the two structures are distinguished by the c parameter, which is higher for the 2:7 R structure due to the difference in stacking ( The analysis performed with XRD for the nanocrystalline Pr 2 Co 7−x Fe x (x = 0, 0.25, 0.5, 0.75, and 1) compounds annealed at T a = 973 K showed the presence of a main crystallographic phase with the structure of Ce 2 Ni 7 (P6 3 /mmc space group) [69,71]. The peaks found were identified by assigning Miller indices (hkl) to the different peaks recorded.…”

“…Quantitative EXAFS modeling of the local Fe structure in Pr 2 (Co,Fe) 7 was initiated with a comprehensive analysis of the five Co sites in Pr 2 Co 7 obtained in our previous paper [71]. The first interatomic distances around the central Co/Fe atom are listed in Table 2.…”

“…The T C values were around 695 and 667 K, respectively. The T C value was the result of two effects: the electronic effect related to the filling of the 3d band of Fe atoms and the magnetovolume effect related to the Co-Co distances [71]. The M(H) curves of the nanocrystalline Pr 2 Co 7−x Fe x compounds were measured at 293 K. The determination of M S was performed using the law of approach to saturation [77]:…”

“…The experimental data corresponded well to the theoretical forecast. The evolution of µ s with x could be justified by the reduction in the average number of 3d electrons when replacing the Co atoms with Fe, which led to a progressive strengthening of the Co(3d)-Co(3d) exchange interactions and, thus, to an enhanced magnetic moment with the 3d [71]. We realized the XRD patterns of Pr 2 Co 7−x Fe x powders that were magnetically aligned at T = 293 K in a field of 0.5 T. For samples with x < 0.5, the (00l) reflections were heavily enhanced, indicating EMD along the c axis.…”