Manipulation of magnetocaloric and elastocaloric effects in Ni–Mn–In alloys by lattice volume and magnetic variation: Effect of Co and Fe co-doping

Abstract

The effects of Co and Fe co-doping Ni–Mn–In alloy on the phase stability, lattice parameters, magnetic properties, and electronic structures are systematically investigated by using the first-principles calculations. Results indicate that Fe atoms replace the excess Mn2 atoms by direct and indirect coexistence (Fe→Mn2 and Fe→In→Mn2); Co substitutes the Ni atoms by direct substitution (Co→Ni) for the Ni–Mn–In alloy. The austenites all exhibit the ferromagnetic (FM) state for the studied compositions. The NM martensites are in the ferrimagnetic (FIM-1) state for the Ni2Mn1.5In0.5, Ni2Mn1.25In0.5Fe0.25, Ni1.75Mn1.5In0.5Co0.25, and Ni1.75Mn1.25In0.5Co0.25Fe0.25 alloys, while the other compositions are in the FM state. The phase stability of austenite and martensite decreases with increasing Co and Fe co-doping. A magnetic-structural coupling transition occurs at x < 0.25 and y < 0.25. The Ni1.91Mn1.5In0.5Co0.08 and Ni1.91Mn1.42In0.5Co0.08Fe0.08 alloys exhibit an A→6M→NM transformation, accompanied by a magnetic transition. When Co and Fe are co-doped, the hybridization strength between Co and Fe is greater than that between Co/Fe and Mn. The enhancement of magnetocaloric and elastocaloric effects is favored by larger magnetization difference (∆M) and lattice volume change (∆V/V0). Based on the calculated phase stability, magneto-structure coupling, ∆V/V0 and c/a ratio, one can predict that the Ni2-xMn1.5-yIn0.5CoxFey alloy with Co content 0 ≤ x ≤ 0.25 and Fe content 0 ≤ y ≤ 0.05 is predicted to have good magneto-controlled functional behavior.