Magnetic interactions in the martensitic phase of Mn rich Ni-Mn-In shape memory alloys

Abstract

The magnetic properties of Mn2Ni (1+x) In (1−x) (x = 0.5, 0.6, 0.7) and Mn (2−y) Ni (1.6+y) In0.4 (y = -0.08, -0.04, 0.04, 0.08) shape memory alloys have been studied. Magnetic interactions in the martensitic phase of these alloys are found to be quite similar to those in Ni2Mn (1+x) In (1−x) type alloys. Doping of Ni for In not only induces martensitic instability in Mn2NiIn type alloys but also affects magnetic properties due to a site occupancy disorder. Excess Ni preferentially occupies X sites forcing Mn to the Z sites of X2YZ Heusler composition resulting in a transition from ferromagnetic ground state to a state dominated by ferromagnetic Mn(Y) -Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions. These changes in magnetic ground state manifest themselves in observation of exchange bias effect even in zero field cooled condition and virgin magnetization curve lying outside the hysteresis loop.

Effect of site occupancy disorder on martensitic properties of Mn2NiIn type alloys: X-ray absorption fine structure study

“…But this general picture could not explain the complete suppression of martensitic transformation in Mn 2−y Ni 1.6+y In 0.4 due to small increase in Mn concentration at the expense of Ni (−0.1 < y < 0) [45]. This is especially important because, the alloy with y = 0 is martensitic with a transformation temperature of ∼ 230K which increases with increase in Ni concentration (y > 0).…”

“…A detailed study of magnetic properties of these alloys along with Mn 2 Ni 1+x In 1−x (x = 0.5, 0.6 and 0.7) has been already presented in Ref. 45. To understand these changes in martensitic transformation temperature, experimental XAFS data recorded at the Mn K and Ni K edges at room temperature in each of these alloys have been compared with calculated Mn and Ni XAFS data using FEFF.…”

“…• and were found to be single phase [45]. Magnetization measurements were performed in the temperature interval 5 K -400 K using a vibrating sample magnetometer in 100 Oe applied field during the zero field cooled (ZFC) and subsequent field cooled cooling (FCC) and field cooled warming (FCW) cycles.…”

“…In our recent work [45], the magnetic properties of Mn 2 Ni 1+x Z 1−x alloys in the martensitic state were found to be similar to those of Ni 2 Mn 1+x In 1−x and this was conjectured to be due to site occupancy disorder arising out of preferential occupation of X sites by Ni atoms. But this general picture could not explain the complete suppression of martensitic transformation in Mn 2−y Ni 1.6+y In 0.4 due to small increase in Mn concentration at the expense of Ni (−0.1 < y < 0) [45].…”

“…Though martensitic transformation has been observed in Mn 2 NiGa (T M ∼ 270K, T C = 588K) [39] the same is not observed in other Mn 2 NiZ alloys where Z = In or Sn. However, increasing of Ni content at the expense of Z atoms to realize alloys of the type Mn 2 Ni 1+x Z 1−x leads to martensitic instability in them [43][44][45].…”