Disorder-Driven Magnetic Properties of Co₂TiSi and Co₂TiAl Heusler Alloys

Many physical properties behave differently in disorder systems from the order one. The effects of atomic disorder on the magnetic properties have been explored on Co₂TiSi and Co₂TiAl full Heusler alloys. Co₂TiSi crystallizes in an ordered L2₁ crystal symmetry, and Co₂TiAl mainly possesses a B₂ structure. The B₂ disorder affects not only the magnetic ordering but also the saturation magnetization, causing the deviation from the Slater-Pauling prediction for Co₂TiAl. The critical exponents of the magnetic phase transition have been analyzed by employing different techniques like, the Arrott plot, Kouvel–Fisher plot, critical isotherm analysis, scaling magnetic behavior, and magnetocaloric analysis as well. The calculated critical exponents are close to the mean field theory which implies long-range ferromagnetic ordering in Co₂TiSi. However, the exchange interaction in Co₂TiAl deviates from the long-range mean field theory. This may be due to the magnetic contribution of the B₂-disordered phase. In addition to the magnetic ordering, the magnetocaloric analysis provides the applicability of Co₂TiSi alloy as a low-cost, hysteresis-free magnetic refrigerant with a large working temperature near room temperature.