Effect of Ni/Mn ratio on phase transformation and magnetic properties in Ni–Mn–In alloys

Abstract

The effect of variation in Ni/Mn ratio on structure, phase transformation, and magnetic properties was investigated in the Ni50−xMn37+xIn13 alloys. Small change in the Ni/Mn ratio drives the structure from martensite of tetragonal L10 to austenite of cubic L21 at room temperature. With decrease in Ni/Mn ratio or increase in Mn content the martensitic transformation temperature was found to decrease and the alloys do not undergo phase transformation below a critical value (7.86) of valence electron concentration (e/a). Temperature and field dependence of magnetization data reveals the complex magnetic nature arising from the coexistence of ferromagnetic and antiferromagnetic interactions in the system. It was found that the effect of Ni/Mn and Mn/In ratios on phase transformation and magnetic properties in Ni–Mn–In alloys is similar if the e/a value of the alloy system remains unchanged.

Designing a New Ni-Mn-Sn Ferromagnetic Shape Memory Alloy with Excellent Performance by Cu Addition

“…This result obviously indicates that substitution of proper Cu for Sn converts antiferromagnetic austenite to ferromagnetic state in the cubic austenite phase, and hence increases the magnetization of austenite. Meanwhile, it can be seen that the equilibrium lattice constants of Ni 16 Mn 12 Sn 4−x Cu x alloys (x = 0, 1, 2, 3, and 4) decrease with increasing Cu content. Probably because the radius of Cu (1.57 Å) is smaller than that of Sn (1.72 Å), the addition of Cu causes the unit-cell volume to shrink.…”

“…In both structures, the AP states are lower on the energy scale and are thus significantly more stable than the P states around the equilibrium lattice parameter for the case of x = 0 and 1. This indicates that the magnetic moment of the Mn Sn in Ni 16 Mn 12 Sn 4−x Cu x alloys (x = 0, and 1) cubic phase is anti-ferromagnetically coupled to the magnetic moment of Mn Mn . On the contrary, as for the case of x = 2, the P states are slightly lower on the energy scale than the AP states with nearly the same energy corresponding to the ground state lattice constant of~6.0 Å.…”

“…To determine the magnetic ground and theoretical lattice parameter of Ni 16 Mn 12 Sn 4−x Cu x alloys (x = 0, 1, 2, 3, and 4) in the austenitic phase, we performed total energy calculations with spin polarization. We considered two situations where the magnetic moments of the excess to the Mn atoms in the Sn sites (denoted as Mn Sn ) are parallel or anti-parallel to the Mn atoms in the Mn sub-lattice site (denoted as Mn Mn ).…”

“…In the model, Mn Mn represents the Mn atoms in the Mn sites, and Mn Sn represents Mn atoms in the Sn sites. In the case of the model of the cubic structure for the austenitic phase of Ni 16 Mn 12 Sn 4−x Cu x alloys (x = 1, 2, 3, and 4), the same size of the model is used except for some appropriate Sn atoms being replaced by the doped Cu atoms. It is worth noting that the simulated structure here is an ordered one, whereas in a real material the Cu and Mn ions on the Sn sites would be randomly distributed.…”

Stress-induced transformation in a Ni-Mn-In alloy and the concomitant change of resistivity

“…An additional decrease of the sample temperature leads to the onset of the martensitic transformation, which LV DFFRPSDQLHG E\ D GURS RI the magnetic susceptibility. It is well known that the low-temperature phase in Ni-Mn-In system is a low-symmetry crystallographic phase with mixed ferromagnetic and antiferromagnetic interactions [9,11]. In an Mn-rich alloy, the excess of Mn atoms relative to the stoichiometric composition results in a partial occupation of the In atomic positions by Mn atoms, which are located at closer distances to the other Mn atoms than in regular sites.…”