Magnetic properties of bulk, and rapidly solidified nanostructured (Nd1-xCex)2Fe14-yCoyB ribbons

Abstract

Magnetic properties of Ce and Co co-doped (Nd 1-x Ce x) 2 Fe 14-y Co y B compounds have been investigated both in bulk polycrystalline and rapidly solidified nanostructured ribbon forms. For certain Ce concentrations the materials exhibit spin reorientation transitions below 140 K. The Curie temperatures, saturation magnetizations, and other magnetic properties relevant for applications as permanent magnets are controlled by Ce and Co substitutions for Nd and Fe, respectively. Most importantly, the results show that Ce, Co co-doped compounds are excellent replacements for several Dy-based high performance permanent magnets (dysprosium is one of the critical elements and is, therefore, in short supply). The high temperature (375 K) magnetic properties for Nd-Ce-Fe-CoB based alloys show promise not only as a replacement for Dy-doped Nd 2 Fe 14 B permanent magnets, but the new alloys also require significantly lower amounts of Nd, which too is the critical element that can be replaced by a more abundant Ce.

Understanding the element segregation and phase separation in the Ce-substituted Nd-(Fe,Co)-B based alloys

“…It means that the two-phase structure disappears after heat treatment. This study well explains why all the reported phase separation phenomena were only observed in the directly quenched alloys 2,16,18 , but not in the single crystal or sintered samples. Hence, our work will make this topic more conclusive 19,32,33 .…”

“…Their steric variation combined with different electron density give rise to the valence state dependent magnetic and metallurgical behaviors of Ce-Nd-Fe-B alloys 14,15 . The last but not the least, an abnormal increase of coercivity has been observed in the Ce-Nd-Fe-B alloys with around 25% Ce-substitution, and several researchers have attributed it to the phase separation 2,16–18 . However, to the best of our knowledge, no microstructural evidence of the phase separation has been reported yet.…”

Manipulating Ce Valence in RE2Fe14B Tetragonal Compounds by La-Ce Co-doping: Resultant Crystallographic and Magnetic Anomaly

“…Since the La 2 Fe 14 B tetragonal structure is unstable121314, the most abundant and cheapest Ce has attracted considerable interest for decades151617181920212223. Different from Pr 3+ , Nd 3+ and La 3+ with stable valence, Ce generally exhibits a mixed valence of 3.44 due to the coexistence of trivalent 4f1 and tetravalent 4f 0 electronic states in Ce 2 Fe 14 B8.…”

“…Stabilizing the Ce 3+ configuration with one localized 4f moment is beneficial for higher intrinsic magnetic properties, thus suppressing the magnetic dilution of Ce-doping RE 2 Fe 14 B compounds. Previous investigations on melt-spun ribbons6101723, hot-pressed618, die-upset618 and sintered magnets1920 have revealed gradually decreased lattice constants of the 2:14:1 phase with increasing Ce content, which can be explained by the smaller lattice parameters of Ce 2 Fe 14 B compound ( a  = 8.76 Å and c  = 12.11 Å) than those of Nd 2 Fe 14 B ( a  = 8.80 Å and c  = 12.20 Å)9. Since the ion radius follows the relation r (Ce 3+ ) >  r (Nd 3+ ) >  r (Ce 4+ ), the monotonic decreasing a and c implies that Ce valence keeps basically unchanged within the whole doping range, otherwise the lattice parameters will deviate from the monotonic variation.…”

Intrinsic Magnetic Properties of Ce2Fe14B Modified by Al, Ni, or Si

“…The low cost and availability of Ce have driven interest in developing Ce-based permanent magnets to replace expensive Nd 2 Fe 14 B magnets in certain applications [7][8][9][10][11][12][13][14][15][16][17][18][19]. This has resulted in investigation of Ce 2 Fe 14 B and its alloys [20][21][22][23][24][25][26].…”