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

The phase relation of LaFe11.5Si1.5 alloys annealed at different high-temperature from 1223 K (5 h) to 1673 K (0.5 h) 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 1423 K. In the temperature range from 1423  to 1523 K, 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 1523 K. With annealing temperature increasing from 1573  to 1673 K, the LaFeSi phase is detected again in the LaFe11.5Si1.5 alloy, and there is La5Si3 phase when the annealing temperature reaches 1673 K. There almost is no change in the XRD patterns of LaFe11.5Si1.5 alloys annealed at 1523 K for 3–5 h. According to this result, the La0.8Ce0.2Fe11.5−xCoxSi1.5 (0≤×≤0.7) alloys are annealed at 1523 K (3 h). 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 266 K. 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 6.8 J/kg K with increasing Co concentration at a low magnetic field of 0–2 T, 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 1223 K (5 h) to 1673 K (2 h).
► The annealing time can be shortening when the annealing temperature is close 1523 K; is different to traditional method.
► The effect of Co on phase and magnetic assets in La0.8Ce0.2Fe11.5−xCoxSi1.5 alloys annealed at 1523 K (3 h) is first studied.