Effect of Ti substitution for Co on structural, magnetic, and electronic properties of Co2FeAl Heusler alloy

Abstract

In pursuit of materials with high spin polarization, Ti substitution for Co in Co₂FeAl was explored to tune the minority spin bandgap near the Fermi level. Consequently, bulk Co_2-xFeTi_xAl (x = 0.00 to 1.00) alloys were synthesized by arc melting followed by heat treatment. Structural analysis showed that the alloys with x = 0.00 and 0.25 exhibited partially disordered B2 structure, while alloys with x ≥ 0.50 exhibited highly ordered L2₁–type structure. Ab initio calculations revealed an increase in spin polarization from ∼54 % for x = 0.00 to 100 % in x = 0.50 and 0.75, with a transition to semiconducting behavior with zero spin polarization at x = 1.00. The enhanced spin polarization in x = 0.50 and 0.75 was confirmed by analysis of temperature-dependent electrical resistivity data. For the alloys with x = 1.00, resistivity data indicate a metallic character with zero magnetic moment, contrary to the theoretically predicted semiconducting nature, possibly due to a small amount of atomic disorder. With increased Ti substitution, the saturation magnetization decreased from 4.70 ± 0.04 μ_B/f.u. (for x = 0.00) to ∼0.01 μ_B/f.u. (for x = 1.00), accompanied by a reduction in the effective magnetic anisotropy constant. The Rhodes-Wohlfarth ratio estimated from thermomagnetization measurements further confirmed the higher spin polarization of alloys with x = 0.50 and 0.75, highlighting their potential for advanced spintronic applications.