La ( Fe 1 − x − y Co x Si y ) 13 ingots with x=0.112, 0.154, and 0.170 and y=0.021, 0.042, 0.063, and 0.085 were processed by Ar arc melting and annealing at 1050 °C for different periods of time up to 12 days. For y=0.085, the Curie temperature of the specimens, optimally annealed to develop the cubic NaZn13-type phase, increases from 88 to 149, and 169 °C for x=0.112, 0.154, and 0.170, respectively. By adding La excess, it becomes more facile to eliminate the secondary bcc (Fe,Co) phase by annealing at 1050 °C, while the structure contains more La(Fe,Co)Si nonmagnetic precipitates. With the decrease in the Si content, it becomes harder to form the La(Fe,Co,Si)13 phase and the morphology of secondary phases are more complex with La(Fe,Co)Si precipitates in form of stripes within La3Co inclusions. Selected La(Fe0.745Co0.17Si0.085)13 ribbons prepared by melt spinning and annealed for a shorter time than ingots maintain residual bcc (Fe,Co) phase. The largest peak in magnetic entropy change occurred at 161 °C with 3.5 J/kg K for La(Fe0.767Co0.170Si0.063)13 specimens with the optimal 1:13 structure, under a field variation of 17 kOe. The peak of magnetic entropy change in annealed ribbons was smaller and broader than in the annealed ingot counterparts.

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