Studies of short-time and high-temperature annealing and magnetic property of LaFe_(11.4)Si_(1.6) compound

The LaFe11.4Si1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K （5 h） to 1623 K （2 h）. The powder X-ray diffraction （XRD） and microstructure observations show that large amount of 1：13 phase begins to appear in the LaFe11.4Si1.6 compound annealed at 1423 K （5 h）. In the temperature range from 1423 K to 1523 K, the α-Fe and LaFeSi phases rapidly decrease to form 1：13 phase. The LaFeSi phase is rarely observed by XRD when the as-cast compound is annealed at 1523 K （5 h）. With annealing temperature increasing to 1573 K, LaFeSi phase is detected again in LaFe11.4Si1.6 compound. In LaFe11.4Si1.6 compounds annealed at 1523 K （5 h）, at 1373 K （2 h）＋1523 K （5 h）, and 1523 K （7 h）＋1373 K （2 h）, the impurity phases including small amount of α-Fe and LaFeSi phase reduce in turn. The magnetic measurement shows that LaFe11.4Si1.6 compounds annealed by above three processes keep the first-order of magnetic transition behavior, and Tc are both at about 200 K. But the values of the maximal ASM（T, H） of has large difference, they are 9.94, 12.66, and 13.96 J/（kg.K） under a magnetic field of 0- 2 T, respectively.

Effect of Ce,Co,B on formation of LaCo_(13)-structure phase in La(Fe,Si)_(13) alloys

The effect of Ce, Co, and B on the formation of 1：13 phase in La（Fe, Si）13 alloys was investigated by XRD, SEM and EDS. The results show that Co can improve the formation of 1：13 phase in as-cast LaFe11.6-xCoxSi1.4 alloys, but in as-cast and annealed LaFe11.6Si1.4-xCox alloys, it will hamper the formation of 1：13 phase and help the formation of a-Fe（Co, Si） solid solution. Ce2Fel7 phases will form when x reaches a certain value in as-cast and annealed La1-xCexFe11.5Si1.5 alloys. B can improve the formation of 1：13 phase accompanied with Fe2B phase in as-cast LaFe11.6-xBxSi1.4 alloys. B improves the formation of a-Fe solid solution in LaFe11.6Si1.4-xBx alloys, and there is almost only a-Fe in as-cast and annealed LaFe11.6Si0.9B0.5 alloy. In all, the introduction of Co, B, and Ce cannot eliminate the a-Fe phases in corresponding alloys prepared by the high-temperature and short-time annealing process.

Effects of the excess iron on phase and magnetocaloric property of LaFe_(11.6*x)Si_(1.4) alloys

The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and vibrating-sample magnetometer （VSM）, respectively. The results showed that the excess Fe would make the 1：13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFelL6＊xSil.4 alloys. The LaFel 1.6.xSil.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFel 1.6,xSil.4 alloys with x=1.05 and 1.1, respectively.

Influence of iron on phase and magnetic property of the LaFe_(11.6)Si_(1.4) compound

The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex＊11.6Si1.4 （x=0.96, 0.98, 1.0, and 1.02） compounds prepared by arc-melting and then annealed at 1423 K （1.5 h）＋1523 K （4.5 h） were investigated. The main phase was NaZn13-type phase, the impurity phases included a small amount of α-Fe and LaFeSi phase in four samples. The crystal cell parameters of 1：13 phase increased from 1.1433（5） to 1.1454（4） nm with x increasing from 0.96 to 1.02, respectively. All samples kept the typical first-order magnetic transition. The increase of Fe strengthened IEM behavior, and led to the remarkable enhancement of MCE effect and negative slopes in Arrott plots around TC. The maximum ΔSM （T, H） under a low magnetic field （0–2 T） was 15.3, 16.8, 17.9, and 24.7 J/kg K with increasing of Fe content from x=0.96 to 1.02, respectively.