Full Variation of Site Substitution in Ni-Mn-Ga by Ferromagnetic Transition Metals

Abstract

Systematic doping by transition elements Fe, Co and Ni on each site of Ni2MnGa alloy reveal that in bulk material the increase in martensitic transformation temperature is usually accompanied by the decrease in ferromagnetic Curie temperature, and vice versa. The highest martensitic transformation temperature (571 K) was found for Ni50.0Mn25.4(Ga20.3Ni4.3) with the result of a reduction in Curie temperature by 55 K. The highest Curie point (444 K) was found in alloy (Ni44.9Co5.1)Mn25.1Ga24.9; however, the transition temperature was reduced to 77 K. The dependence of transition temperature is better scaled with the Ne/a parameter (number of non-bonding electrons per atom) compared to usual e/a (valence electrons per atom). Ne/a dependence predicts a disappearance of martensitic transformation in (Ni45.3Fe5.3)Mn23.8Ga25.6, in agreement with our experiment. Although Curie temperature usually slightly decreases while the martensitic transition increases, there is no significant correlation of Curie temperature with e/a or Ne/a parameters. The doping effect of the same element is different for each compositional site. The cascade substitution is discussed and related to the experimental data.

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

“…The spin-down Ni peak at the Fermi level that contributes to the austenite phase instability is a half-filled antibonding orbital due to Ni d -Ni d and Ni d -Ga p interactions (Fig. 5 b,e) in agreement with theory 14 and experiment 63 , 64 .…”

“…The d-d splitting in the Ni-Mn interaction is weaker, and the occupied spin-up t * 2g antibonding states are weakening this bond. The spin-down Ni peak at the Fermi level that contributes to the austenite phase instability 5b,e) in agreement with theory 14 and experiment 63,64 .…”

Electronic transport evolution across the successive structural transitions in Ni50–xFexTi50 shape memory alloys

“…Similarly, Fe doping in Heusler alloy (Ni 45.3 Fe 5.3 ) Mn 23.8 Ga 25.6 stabilized the austenitic phase down to 10 K with the vanishing of MT due to the addition of Fe. [28] In Ni 50−x Fe x Mn 40 Sn 10 (x = 0, 2, 4, 6, 8 at.%) melt-spun ribbons, the T MT decreases with the increase in Fe doping. [29] Table 1.…”

Experimental Observations versus First‐Principles Calculations for Ni–Mn–Ga Ferromagnetic Shape Memory Alloys: A Review

“…[32] Regarding alloying by additional elements, the main experimental conclusion is that alloying by a single element can strongly increase the martensitic transformation temperature while decreasing the ferromagnetic Curie point or vice versa. [113] Thus, a more promising approach appeared to be alloying with combinations of transition metals. [114,115] At the same time, however, adding more than 5 at% of transitional metals often results in the precipitation of secondary phases or the unwanted prevalence of the NM structure.…”