Electrical-and magneto-transport across the thermo-elastic martensitic transformation in anti-site-disordered off-stoichiometric Co–Fe–Ti–Si Heusler alloy thin films

Abstract Anti-site disorder (ASD), present in Heusler alloy thin films, is known to significantly affect their physical properties, but a complete understanding of the actual role of ASD is still lacking. In this work, we systematically investigate the effect of ASD on electrical resistivity ρ ( T ) and transverse magnetoresistance MR ⊥ in off-stoichiometric Co–Fe–Ti–Si (CFTS) thin films across the thermo-elastic martensitic phase transformation (MPT). The CFTS films with A2 ASD exhibit a negative temperature coefficient of resistivity (n–TCR) and an upturn below ∼ 30 K. In sharp contrast, the partially L2 1 -ordered films are metallic in nature, characterized by a resistivity minimum at low temperatures ( T min ≅ 30 K) and a positive TCR for T > T min . The change in the sign of TCR finds a straightforward explanation in terms of the competition between the quantum corrections (weak localization, electron–diffusion scattering) and the ballistic scattering mechanisms (electron–magnon, e − m , and electron–phonon, e–p). We find that, stronger the atomic ASD, more prominent the quantum corrections and the weaker the scattering of e − m and e–p scattering. All the CFTS films exhibit a distinct thermal hysteresis and a significant drop in resistivity, symptomatic of a MPT, near the characteristic temperatures: martensite-end T Me ≅ 300 K and austenite-begin T Ab ≅ 325 K. Regardless of the strength of ASD, in the martensite phase the anti-symmetric (ASMR) component of MR ⊥ ( H ) dominates over the symmetric (SMR) counterpart, whereas the reverse is true (i.e. SMR ≫ ASMR ) for the austenite phase at temperatures T Ab ≅ 325 K