Effects of solidification rate and excessive Fe on phase formation and magnetoclaoric properties of LaFe11.6xSi1.4

The effects of solidification rate and excessive Fe on phase formation and magnetocaloric properties of LaFe11.6xSi1.4 (x=1.1, 1.2) were investigated by XRD, SEM and VSM measurements. The XRD results show that the amount of LaFeSi phase in the as-cast melt-spun ribbons prepared by a copper wheel at a speed of 10 m/s is less than that in the as-cast arc melting buttons with the same x values. The annealed melt-spun ribbons contain smaller amount of La(Fe, Si)13 (1:13) phase than the corresponding annealed arc melting buttons. Although the melt-spun sample has finer crystalline grains of α-Fe, as indicated by SEM analysis, its crystalline size has not reached nano-scale. Therefore, the magnetic exchange-coupling between 1:13 phase and α-Fe phase has not been observed in melt-spun ribbons. Further, the maximum negative magnetic entropy change (-SMax) and relative cooling power (RCP) of annealed melt-spun ribbons under a field change of 0-2 T are weaker than those of the corresponding annealed arc melting buttons.