BCMaterials Fortnightly Seminar #91 Andrés Martín - Ana María Schönhöbel

ANDRÉS MARTÍN

(BCMATERIALS)

Improving NdFe11Ti for permanent magnet applications, by Y substitution and nitrogenation

Rare Earth (RE) Permanent magnets (PM), based in Nd-Fe-B, have an increased demand for electric vehicles and wind generators as well as robots for industry and services, hard drives, refrigerators, phones, etc. Scarcity of RE, categorized as critical raw materials, and environmental problems related with its production have led to the search for new rare earth-free/lean alloys alternatives for permanent magnets. Therefore, a renewed interest has arisen on the REFe12 compounds with tetragonal ThMn12 (1:12) structure. These compounds present an inherent lean content of rare earths (7.7 at.%) compared with Nd2Fe14B (11.8 at.%) magnets. Among the 1:12 compounds, NdFe12 with interstitial N is of special interest as it presents intrinsic hard magnetic properties superior to those of Nd2Fe14B. Binary REFe12 compounds, however, need a third element, such as Ti, Mo, Si or V, to stabilize the 1:12 structure. Such a third element reduces the saturation magnetization and the Curie temperature of the alloy. Using Ti, only one atom per formula is enough for stabilizing the phase, leading to better magnetic properties among other stabilizing elements. Recent theoretical predictions indicate that substituting Y for Nd in Nd1-xYxFe11Ti will greatly improve the magnetic anisotropy. The preference of N atoms to sit between Y atoms, instead of Nd ones, also hints for an easier nitrogenation in presence of Y. In this work we report the synthesis of Nd0.5Y0.5Fe11Ti, by arc-melting of the pure constituents, followed by an annealing at 1175 ºC to obtain the 1:12 structure. This alloy was afterwards nitrogenated at different times and temperatures to improve its magnetic properties. Best results yield an increase of the magnetic anisotropy field from 1.75 T to over 3 T, while the Curie temperature increased from 270 ºC up to 390 ºC. These properties open great perspectives for PM applications.

ANA MARÍA SCHÖNHÖBEL

(BCMATERIALS)

Intrinsic Magnetic Properties of SmFe12-xVx Alloys with reduced V-content

For the past couple of years, we have been focusing our studies on R(Fe,M)12 compounds with the aim to develop a rare earth-lean permanent magnet. In this work, we present the results obtained on SmFe12-xVx (x=0.5-2.0) alloys with the 1:12 structure. We have been able to synthesize for the first time the SmFe11V compound with a nearly pure 1:12 phase. The SmFe11V compound has a Curie temperature of 634 K, and saturation magnetization of 115 A m2/kg (1.12 T). An anisotropy field of around 12 T with an anisotropy constant of 5.3 MJ/m3 have been obtained in magnetically-oriented fine powders.