Probing Structural and Magnetic Instabilities and Hysteresis in Heuslers by Density Functional Theory Calculations

Abstract

Martensitic transformations of rapidly quenched and less rapidly cooled Heusler alloys of type Ni-Mn-X with X ¼ Ga, In, and Sn are investigated by ab initio calculatioms. For the rapidly cooled alloys, we obtain the magnetocaloric properties near the magnetocaloric transition. For the less rapidly quenched alloys these magnetocaloric properties start to change considerably, each alloy transforms during temper-annealing into a dual-phase composite alloy. The two phases are identified to be cubic Ni-Mn-X and tetragonal NiMn.

Properties and Decomposition of Heusler Alloys

“…This may lead to time‐dependent effects such as, for example, supercells with non‐stoichiometric composition showing strong atomic relaxations because of the non‐cubic environment of the individual atoms. This directly probes the effect of disorder and may cause the onset of segregation for alloys close to the martensitic transformation (this may also trigger the L2 1 ‐B2 transformation of Ni–Mn–In, Ni–Mn–Al, and Ni–Mn–Ga). The decomposition into a dual‐phase composite alloy is a very peculiar type of decomposition but appears to be lowest in energy.…”

“…In this article, we review mostly Ni–Mn–In and Ni–Co–Mn–Sn and the corresponding metamagnetic effects following their large magnetocaloric effect properties and high level of sensitivity of transformation characteristics (e.g., B2–L2 1 and martensitic details in dependence of the microstructural changes, anti‐site defects, and potential role of vacancies), which have been discussed recently . This article is based on reviewing, in particular, details of decomposition, segregation, and time‐dependent effects reported previously …”

“…We present some recent results of ab initio calculations, in particular, of the segregation processes that some of the Heusler alloys as Ni–Mn–In and Ni–Mn–Sn exhibit, and describe the physical properties of rapidly quenched magnetic Heusler alloys with their frozen compositional disorder and competing magnetic interactions. These arise in particular from the excess Mn atoms occupying the sites of the Z element in Ni–Mn– Z with Z =Al, Ga, In, Sn, Sb (see Figure …”

“…[8][9][10][11][12][13][14][15] In this article,w e review mostlyN i-Mn-In and Ni-Co-Mn-Sn and the correspondingm etamagnetic effects following their large magnetocaloric effect properties [16,17] and high level of sensitivity of transformation characteristics (e.g., B2-L2 1 and martensitic details in dependence of the microstructural changes,a ntisite defects,a nd potential role of vacancies), which have been discussed recently. [18] This articlei sb ased on reviewing, in particular, details of decomposition, [11][12][13][14][15] segregation, [19] and time-dependenteffects reported previously. [20,21] Ferroic materials allow for significant adiabatic temperature changes induced by realistic electrical and magnetic fields,b ye xternal stress and under pressure.…”

“…We presents ome recent results of ab initio calculations,i n particular, of the segregation processes that some of the Heusler alloys as Ni-Mn-In and Ni-Mn-Sn exhibit, [19] and describe the physical properties of rapidlyq uenched magnet-Martensitic transformations of rapidly quenched and lessrapidlyc ooled Heusler alloys of type Ni-Mn-X with X = Ga, In, and Sn are investigated by ab initio calculations.F or alloys rapidly cooled from 1173 K, we obtain the well-known magnetocaloric properties near the magnetocaloric phase transition. Fort he less-rapidly cooled alloys with secondary heat treatment these magnetocaloric properties start to changec onsiderably,b ecause each alloy transformsd uring temper-annealing into ad ual-phase composite alloy.T hese two phases are identified to be cubic stoichiometric Ni 2 MnX and tetragonal disordered NiMn.…”