Magnetic properties of LaFe2−xCoxSi: A new two-phase naturally formed composite alloy

We report the effect of Fe by Co substitution on the structural and magnetic properties of the two-phase “composite” alloy LaFe2−xCoxSi as prepared by the suction casting technique. This alloy contains LaFe13−x−yCoxSiy (cubic NaZn13-type) and LaFe1−xCoxSi (tetragonal CeFeSi-type) as constituents, with a compositional ratio between the two phases of ≈40 wt. % NaZn13-type and ≈60 wt. % CeFeSi-type; this ratio remains relatively the same for all the compositions investigated despite the Co content. As expected, while the Co-doping in LaFe2−xCoxSi increases the Curie temperature from 199 K (at H = 20 kOe) and 215 K (at H = 50 kOe) for the pure LaFe2Si, to 274 K (at H = 20 kOe) and 277 K (at H = 50 kOe) for the Co substituted LaFe1.7Co0.3Si alloy, it has the opposite effect on the magnetocaloric effect, reported in terms of the magnetic entropy change (ΔSM), which decreases with increasing the Co content. The full width at the half-maximum value of magnetic entropy changes also increases significantly with Co doping going from 14 K (at H = 20 kOe) in the pure LaFe2Si alloy to 46 K (at H = 20 kOe) in the Co-doped LaFe2−xCoxSi. The magnetic and magnetocaloric properties of LaFe2−xCoxSi alloys for x = 0, 0.1, 0.2, and 0.3 are discussed in this article.