Effect of partial substitution of silicon by other sp-valent elements on structure, magnetic properties and electrical resistivity of Co₂FeSi Heusler alloys

Highlights: • Effect of sp valent element substitution for Si in Co₂FeSi Heusler alloy was investigated. • All alloys except Co₂FeSi_0.5Sn_0.5 show single phase L2₁ structure with small B2 disorder. • Atomic radius of substitutional element does not have a systematic influence on properties. • Co₂FeSi_0.5Ge_0.5 and Co₂FeSi_0.5Ga_0.5 are the best choices for half metallic ferromagnets. - Abstract: The effect of partial substitution (50%) of Si by other sp-valent elements such as Al, Ga, Ge, In and Sn on structure, magnetic properties and electrical resistivity of full Heusler type Co₂FeSi alloys was investigated. The results revealed that these alloys (except Sn substituted alloy) consist of mostly L2₁ ordered phase along with some B2 type disordered phase. The highest L2₁ ordering was seen in Co₂FeSi_0.5Ge_0.5 alloy. The magnetization studies showed all alloys obey the Slater–Pauling rule at 4 K except for Sn substituted alloy. However, at room temperature, only Ga, Ge and Al substituted alloys followed the Slater–Pauling rule. Electrical transport studies revealed the presence of half-metallic behavior at low temperatures in all alloys. However, half-metallicity was preserved to some extent at room temperature only in Ga and Ge substituted Co₂FeSi alloys