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

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.

Anomalously large magnetic moment in nanocrystalline Co0.3Zn0.7Fe2O4thin films

“…This indicates that for our film, not only the magnetic moment but T C is also higher than bulk. In order to further confirm if T C of the film is indeed higher than the bulk in the T S =750°C film, we measured magnetization of this film and that of bulk as a function of temperature (M-T) in an applied field of 1 kOe [30]. Figure 5(b) shows the dM/dT versus T curves of these materials.…”

Magnetic hardening of Nd-Ce-Fe-B films with high Ce concentration

“…In this work, we successfully prepared the high-performance Nd-Ce-Fe-B film with a high Ce concentration of more than 50 wt.% Ce substitution. Although important progresses have been made 6 – 9 , 11 , 13 – 15 , the magnetic properties of Ce magnets with a Ce-substitution proportion higher than 50 wt.% are still low. The magnetic properties achieved in our film (see Fig.…”

“…This magnet shows a good cost-performance in comparison with a 48.9 MGOe La/Ce-free commercial magnet 14 . It is also found that the La-Ce doping conduces to the magnetically favorable Ce 3+ state 15 . For 50 wt.% La, Ce and La-Ce substitution (La/Ce ratio is 1.86), sintered magnets achieve the coercivity of 0.8 kOe, 5.7 kOe and 6.6 kOe, respectively 15 .…”

“…It is also found that the La-Ce doping conduces to the magnetically favorable Ce 3+ state 15 . For 50 wt.% La, Ce and La-Ce substitution (La/Ce ratio is 1.86), sintered magnets achieve the coercivity of 0.8 kOe, 5.7 kOe and 6.6 kOe, respectively 15 . With the variation of Ce, La and La-Ce substitution content, an abnormal increase of coercivity has been observed 9 , 11 , 13 , 16 .…”

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

“…reported a mixed-valent state with the coexistence of Ce 3+ and Ce 4+ atoms in the Ce 2 Fe 14 B phase based on the evidence provided by Ce L 3 -edge x-ray absorption near-edge structure measurement 13 . 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 .…”