The effect of different temperature annealing on phase relation of LaFe11.5Si1.5 and the magnetocaloric effects of La0.8Ce0.2Fe11.5−xCoxSi1.5 alloys

• Published in: Journal of magnetism and magnetic materials 2011-12, Vol.323 (24), p.3177-3183
• Main Authors: Chen, Xiang, Chen, Yungui, Tang, Yongbai
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; High-temperature and short-time annealing; Hysteresis; La0.8Ce0.2Fe11.5−xCoxSi1.5 alloy; Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.); Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Magnetocaloric effect; Magnetocaloric effect, magnetic cooling; Physics
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2011.05.041

The phase relation of LaFe11.5Si1.5 alloys annealed at different high-temperature from 1223K (5h) to 1673K (0.5h) has been studied. The powder X-ray diffraction (XRD) patterns show that large amount of 1:13 phase begins to form in the matrix alloy consisting of α–Fe and LaFeSi phases when the annealing temperature is 1423K. In the temperature range from 1423 to 1523K, α–Fe and LaFeSi phases rapidly decrease to form 1:13 phase, and LaFeSi phase is rarely observed in the XRD pattern of LaFe11.5Si1.5 alloy annealed at 1523K. With annealing temperature increasing from 1573 to 1673K, the LaFeSi phase is detected again in the LaFe11.5Si1.5 alloy, and there is La5Si3 phase when the annealing temperature reaches 1673K. There almost is no change in the XRD patterns of LaFe11.5Si1.5 alloys annealed at 1523K for 3–5h. According to this result, the La0.8Ce0.2Fe11.5−xCoxSi1.5 (0≤×≤0.7) alloys are annealed at 1523K (3h). The analysis of XRD patterns shows that La0.8Ce0.2Fe11.5xCoxSi1.5 alloys consist of the NaZn13-type main phase and α–Fe impurity phase. With the increase of Co content from x=0 to 0.7, the Curie temperature TC increases from 180 to 266K. Because the increase of Co content can weaken the itinerant electron metamagnetic transition, the order of the magnetic transition at TC changes from first to second-order between x=0.3 and 0.5. Although the magnetic entropy change decreases from 34.9 to 6.8J/kgK with increasing Co concentration at a low magnetic field of 0–2T, the thermal and magnetic hysteresis loss reduces remarkably, which is very important for the magnetic refrigerant near room temperature. ▸ Effect of different high-temperature and short-time annealing on LaFe11.5Si1.5 from 1223K (5h) to 1673 K(2h). ▸ The annealing time can be shortening when the annealing temperature is close 1523K; is different to traditional method. ▸ The effect of Co on phase and magnetic assets in La0.8Ce0.2Fe11.5−xCoxSi1.5 alloys annealed at 1523K (3h) is first studied.