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 asymptotic to 40 wt. % NaZn13-type and asymptotic to 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 (delta S-M), 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.