Magnetic properties enhancement of α-Fe/Nd2Fe14B-type nanocomposites by Co substitution

Abstract

The phase evolution and magnetic properties of melt-spun Nd9.5(Fe1−xCox)85.5B5 (x=0, 0.05, 0.1, and 0.15) nanocomposites have been investigated. It was found that Co substitution for Fe, i.e., x=0.05–0.15, improves the Curie temperature (Tc), remanence (Br), and maximum energy product (BH)max of the materials obtained. Co substitution for Fe was found to promote grain coarsening, after thermal processing, in materials with a high Co concentration. Wohlfarth remanence analysis suggests that dilute-Co substitution for Fe increases the strength of the exchange coupling between the soft magnetic phases, α-(Fe, Co) and Nd2(Co, Fe)17, and the 2:14:1 phases. The increase in the saturation magnetization of α-(Fe, Co) and 2:14:1 phase, in conjunction with the enhanced exchanged coupling, presumably, result in an increased (BH)max of Nd9.5(Fe0.95Co0.05)85.5B5 and Nd9.5(Fe0.90Co0.10)85.5B5 samples. Once above a critical Co concentration, for the compositions studied, the strength of exchange coupling interactions between magnetically soft and hard phases does not seem to vary significantly with Co content. Moreover, both the irreversible loss of induction and reversible temperature coefficient of induction (conventionally referred to as α) of fully processed materials decrease with increasing Co concentration.

Beneficial effect of the substitution of Co for Fe on the magnetic properties of melt-spun Pr2Fe14C/α-Fe-type nanocomposite magnets

“…Correspondingly, it is found that the remanence of the ribbons displays a similar tendency with the increase of x. A similar phenomenon was also observed in the Nd 2 Fe 14 B/␣-Fe-type nanocomposites [6]. …”

“…A heat treatment applied to selected ribbons at 650-750 • C for 10 min cause them to crystallize, improving their magnetic properties. Characterization techniques for the ribbons were reported elsewhere [6].…”

“…If the intergranular exchange coupling is strong enough, the magnetic properties of nanocomposites can be enhanced by optimizing the intrinsic properties of the magnetic phases such as saturation magnetization and anisotropy field [4,5]. Many experimental results show that a moderate substitution of Co for Fe can increase the saturation magnetization (at room temperature) of magnetically hard and soft phases, and so significantly improve the magnetic properties of (Nd, Pr) 2 Fe 14 B/␣-Fe nanocomposites [6][7][8][9]. The crystal structure of the Pr 2 Fe 14 C phase is analogous to that of the (Nd, Pr) 2 Fe 14 B compounds.…”

Enhancement of the exchange coupling interaction of nanocomposite Nd2Fe14B/α-Fe magnets by a small amount of Sm substitution for Nd

“…However, it is emphasized here that Sm decreases the magnetocrystalline anisotropy field and saturation magnetization, so the coercivity and remanence of Nd 7.8 Sm 0.2 Fe 86 B 6 ribbons are lower than that of pure Nd 8 Fe 86 B 6 ribbons. This could be improved by substitution of Co for Fe and substitution of Dy for Nd [16,17].…”

Microstructure and magnetic properties of (Nd1−yPry)4.5Fe77B18.5 nanocomposite alloys

“…A disadvantage of the nanocomposite alloys is the decrease in i H c accompanying the M r enhancement, which adversely affects (BH) max , in spite of the continuing increase in M r . Many attempts have been made to improve i H c and (BH) max of the nanocomposites further by elemental substitution [7][8][9][10][11]. One such attempt is partial replacement of Nd by Pr or Dy rare earth elements.…”