The effect of Co-doping on martensitic transformation temperatures in Ni–Mn–Ga Heusler alloys

Abstract

The effect of Co-doping in non-stoichiometric Ni–Mn–Ga alloys on martensitic transformation temperatures is investigated. Experimental results show that the effect of Co addition on martensitic transformation temperatures is remarkable, but the Heusler structure of the alloys remains unchanged. For Ni48Mn27Ga25−xCox (x = 1, 2, 3, 4) alloys, the martensitic transformation temperatures increase monotonically with increasing Co substitution for Ga. The effect can be attributed to the variation of intrinsic factors, i.e. the decrease in the unit-cell volumes and the increase in the electronic concentrations and density. The martensitic transformation temperatures of Ni48Mn26−xCoxGa26 (x = 1, 2, 3, 5) alloys do not change much with the variation of Co substitution and intrinsic factors have no effect on the exceptional behaviour, which implies that many factors should be considered simultaneously when designing practical alloys.

Fe and Co selective substitution in Ni2MnGa: Effect of magnetism on relative phase stability

“…Khan et al [62] specifically studied the effect of isoelectronic substitution of Ga by In in Ni 2 MnGa and concluded that the effect of Z on M s mainly arise from the change of unit cell volume which modifies the relative position of the Brillouin zone boundary and Fermi surfaces. The role of volume effects on the martensitic transition has been further studied via doping of Ni-Mn-Ga with several other elements and use of electron density to parametrize structural transition temperatures has been suggested [63,64]. The effect of magnetism on the martensitic transition, however, has been studied in less detail.…”

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

“…Experiments have demonstrated that the martensitic transformation properties of the Ni 2 MnGa alloys may change drastically by doping of a fourth element such as Fe, Co, and Cu. [1][2][3][4][5][6][7][8][9] For example, the substitution of Mn with Fe (Ni 2 Mn 1−x GaFe x ) up to x = 0.70 drops the martensitic transition temperature T M from 200 K to about 120 K, 1 whereas the replacement of Ga by Fe (Ni 52.7 Mn 22.1 Ga 25.2−x Fe x , x = 5.3) increases T M from 290 K to 440 K. 2 For the Co-and Cu-doped Mn-or Ga-deficient alloys, T M increases, [3][4][5][6] but it decreases if Co or Cu replaces Ni atoms. 2,7,8 The high-temperature austenite of Ni 2 MnGa is of cubic L2 1 structure, consisting of four sublattices: sites ( 1 4 , 1 4 , 1 4 ) and ( 3 4 , 3 4 , 3 4 ) are occupied by Ni, ( 1 2 , 1 2 , 1 2 ) by Mn, and (0, 0, 0) by Ga.…”

Composition dependent elastic modulus and phase stability of Ni2MnGa based ferromagnetic shape memory alloys

“…The martensitic transformation temperature T M (K) [7][8][9][10][11][12][13][14][15][16] versus the tetragonal shear modulus C′ (in GPa) and e/a of Fe/Co/Cudoped Ni 2 MnGa alloys [38]. general T M~C ′ correlation works for this alloy.…”

“…21) increases T M from 290 K to 440 K [10]. For the Co and Cu-doped Mn or Ga deficient alloys, T M increases [11][12][13][14], but it decreases if Co or Cu replaces Ni atoms [15,16].…”

“…Again we see that in general, C' decreases with increasing e/a except for Ni 2+x MnGaCu x alloy. We collected the experimental T M of the alloys [9][10][11][12][13][14][15][16] with compositions matching roughly the 9-types of alloys investigated in this work, and plotted them against C' and e/a in Figure 4. It is shown that in general, T M increases with decreasing C' and increasing e/a.…”