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. 2016 Jul 26;6:30194.
doi: 10.1038/srep30194.

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

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Free PMC article

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

Jiaying Jin et al. Sci Rep. .
Free PMC article

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 Ce(3+) state in the composition range of x > 0.3, owing to the co-doping of large radius La(3+) 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.

Figures

Figure 1
Figure 1
(a) XPS spectra of the Ce 3d level in [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B strips with x = 0.1∼0.5. (b) The derived intensities of formula image (circles in red color), and (formula image) (squares in blue color) are plotted as a variation of La-Ce content x.
Figure 2
Figure 2
Rietveld refinement of step-scanned XRD patterns of [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B powders for (a) x = 0, (b) x = 0.1, (c) x = 0.3, (d) x = 0.4, and (e) x = 0.5 at room temperature. Experimental pattern, calculated pattern, and their differences are given in black, red and blue colors, respectively. Bottom ticks mark the characteristic Bragg positions of RE2Fe14B, Nd, REFe2 and Fe phases, and serve as a guide to the eye.
Figure 3
Figure 3
(a) Enlarged XRD patterns of 2θ between 34.3∼36° for samples (x = 0.2 and x = 0.3). (b) M-T curves for samples (x = 0.2 and x = 0.3) in the temperature range of 200∼300 K. Their corresponding dM/dT-T curves are shown in the top-right insets.
Figure 4
Figure 4
(a) Enlarged rietveld refined XRD patterns of 2θ between 41∼44.2° for [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B powders. (b) Dependences of lattice parameters a, c, c/a ratio and unit cell volume V of the 2:14:1 tetragonal phase on the La-Ce content x.
Figure 5
Figure 5
(a) Initial magnetization curves measured at 295 K, (b) M-T and dM/dT-T curves in the temperature range of 380~670 K, (c) M-T and dM/dT-T curves in the low temperature range of 25∼200 K for [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B (x = 0∼0.5) samples. Inset in (a) is an enlarged view of the high-field regime. (d) The derived saturation magnetization Ms, Curie temperature TC and spin reorientation temperature TSR as a function of La-Ce content x.
Figure 6
Figure 6
(a) DSC curves for specimens with x = 0, 0.1, 0.3, and 0.5 upon heating to 1550 K at 20 K/min, (b) XRD pattern of the as-quenched [(Pr, Nd)0.5(La, Ce)0.5]2.14Fe14B (x = 0.5) strip after annealing at 1250 K for 1 h.

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