Site preference and elastic properties of Fe-, Co-, and Cu-doped Ni2MnGa shape memory alloys from first principles

Abstract

The site preference and elastic properties of Fe-, Co-, and Cu-doped Ni 2 MnGa alloys are investigated by using the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. It is shown that Fe atom prefers to occupy the Mn and Ni sublattices even in Ga-deficient alloys; Co has strong tendency to occupy the Ni sublattice in all types of alloys; Cu atoms always occupy the sublattice of the host elements in deficiency. For most of the alloys with stable site occupations, both the electron density n and the shear modulus C can be considered as predictors of the composition dependence of the martensitic transition temperature T M of the alloys. The physics underlying the composition-dependent C are discussed based on the calculated density of states.

Magnetic Moment of Cu-Modified Ni2MnGa Magnetic Shape Memory Alloys

“…at 110 K in a field of 2 T. The value of μ s at 5 K for Ni 2 MnGa in the present study is in good agreement with the value reported by Ahuja et al [13]. Recently, Li et al investigated theoretically the site preference and elastic properties of Fe-, Coand Cu-doped Ni 2 MnGa alloys by using the first-principles exact muffin-tin orbital method in combination with the coherent-potential approximation [14]. According to the results of the calculation by Li et al [14] [14] are in good agreement with those reported earlier for the stoichiometric Heusler alloy Ni 2 MnGa [15][16][17][18][19][20][21][22].…”

“…The antiferromagnetic coupling between nearest-neighbor Mn atoms in Ni 2 (Mn 1 − y Cu y )(Ga 1 − y Mn y ) alloys is due to the variation of the exchange interaction that becomes antiferromagnetic for small Mn-Mn interatomic distances. This antiferromagnetic coupling was already proved experimentally and theoretically in many Mn-rich Ni-Mn-Ga Heusler alloys [14,[23][24][25][26][27]. Then, the μ s of Ni 2 (Mn 1 − y Cu y )(Ga 1 − y Mn y ) alloys is given by μ s (cal) = 2μ Ni + (1 − y)μ MnI + yμ Cu + (1 − y)μ Ga + yμ MnII , where μ MnI and μ MnII mean the values of the magnetic moment of the Mn atoms on the Mn sublattice and the Ga sublattice, respectively.…”

“…In the above considerations on [14]. Unfortunately, the calculations in [14] were made for the site occupation of Cu-doped Ni 2 MnGa with the L2 1 -type structure, instead of the one with the observed martensitic structure at 5 K. Nevertheless, the above satisfactory agreements between the experimental and calculated concentration dependence of the magnetic moment μ s may rather confirm that the site-occupation configurations in the present analyses exist also in the martensite phase.…”

“…Recently, Li et al investigated theoretically the site preference and elastic properties of Fe-, Coand Cu-doped Ni 2 MnGa alloys by using the first-principles exact muffin-tin orbital method in combination with the coherent-potential approximation [14]. According to the results of the calculation by Li et al [14] [14] are in good agreement with those reported earlier for the stoichiometric Heusler alloy Ni 2 MnGa [15][16][17][18][19][20][21][22]. In order to explain the observed concentration dependence of the magnetic moment for Ni 2 Figure 5 is the one calculated by using this equation.…”

“…As seen in Figure 5, the experimental values are in good agreement with those calculated. [14] for the magnetic moment of the Mn atoms on the Ga sublattice. The antiferromagnetic coupling between nearest-neighbor Mn atoms in Ni 2 (Mn 1 − y Cu y )(Ga 1 − y Mn y ) alloys is due to the variation of the exchange interaction that becomes antiferromagnetic for small Mn-Mn interatomic distances.…”