Magnetocaloric effect and phase transformation of Zn-doped Ni–Mn–Ti all-d metal Heusler alloys.

Ni–Mn–Ti Heusler alloys have gained a great consideration recently due to their important magnetoresistance and magnetocaloric properties. Herein, the structure, martensitic transition (MT), and magnetocaloric effect (MCE) of Ni 50- x Zn x Mn 35 Ti 15 (x = 0, 2, 4, and 6) Heusler alloys have been studied. XRD results show that the studied alloy with x = 0 display a monoclinic (5 M) martensite phase. Besides, the examined alloy with x = 2 presents a combination of monoclinic (5 M) martensite and cubic (B2) austenite phases, whereas the alloys with x = 4 and x = 6 exhibit only a cubic (B2) austenite phase. By increasing Zn content x up to 6, the Curie temperature of austenite decreases from 283 K to 132 K, and the MT temperatures decrease from ferromagnetic austenite to weak-magnetic martensite, which is apparently due to the exchange interaction of Mn–Mn and the low power of d - d hybridization between the A/C and B(D) sites. The best maximum magnetic entropy change (ΔS M, max) and refrigeration capacity (RC) are for the studied alloy with x = 4 (5.22 J kg−1K−1 and 217 J kg−1 at 120 kOe, respectively). The Zn addition not only facilitates the formation of B2-type Heusler phases but also offer the possibility to tune the MT and establish strong ferromagnetic coupling. [Display omitted] • Synthesized Ni(Zn)-Mn-Ti series with varying Ni:Zn ratio. • XRD patterns confirmed that the introduction of Zn stabilizes the austenite phase B2. • Martensitic transition and the Curie temperature of austenite shift to the lower temperatures. • All- d -metal Ni 50-x Zn x Mn 35 Ti 15 (x = 0, 2, 4, and 6) alloys are capable of undergoing a magneto-structural coupling transition. [ABSTRACT FROM AUTHOR]