Abstract
Abundant and low-cost Ce has attracted considerable interest as a prospective alternative for those critically relied Nd/Pr/Dy/Tb in the 2:14:1-type permanent magnets. The (Nd, Ce)2Fe14B compound with inferior intrinsic magnetic properties to Nd2Fe14B, however, cannot provide an equivalent magnetic performance. Since Ce valence is sensitive to local steric environment, manipulating it towards the favorable trivalent state provides a way to enhance the magnetic properties. Here we report that such a desirable Ce valence can be induced by La-Ce co-doping into [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B (0 ≤ x ≤ 0.5) compounds via strip casting. As verified by X-ray photoelectron spectroscopy results, Ce valence shifts towards the magnetically favorable Ce3+ state in the composition range of x > 0.3, owing to the co-doping of large radius La3+ into 2:14:1 phase lattice. As a result, both crystallographic and magnetic anomalies are observed in the same vicinity of x = 0.3, above which lattice parameters a and c, and saturation magnetization Ms increase simultaneously. Over the whole doping range, 2:14:1 tetragonal structure forms and keeps stable even at 1250 K. This finding may shed light on obtaining a favorable Ce valence via La-Ce co-doping, thus maintaining the intrinsic magnetic properties of 2:14:1-type permanent magnets.
Highlights
Since the La2Fe14B tetragonal structure is unstable[12,13,14], the most abundant and cheapest Ce has attracted considerable interest for decades[15,16,17,18,19,20,21,22,23]
Since the ion radius follows the relation r (Ce3+) > r (Nd3+) > r (Ce4+), 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
The Ce valence decreases with expanding site volume, which suggests the potential of tuning Ce valence via alloying[24,25]
Summary
Since the La2Fe14B tetragonal structure is unstable[12,13,14], the most abundant and cheapest Ce has attracted considerable interest for decades[15,16,17,18,19,20,21,22,23]. XPS results verify a valence shift towards the favorable Ce3+ state merely in the composition range of x > 0.3.
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