Temperature and magnetic-field dependence of the elastic constants of Ni-Mn-Al magnetic Heusler alloys

Abstract

We report on measurements of the adiabatic second-order elastic constants of the off-stoichiometric Ni 54 Mn 23 Al 23 single-crystalline Heusler alloy. The variation in the temperature dependence of the elastic constants has been investigated across the magnetic transition and over a broad temperature range. Anomalies in the temperature behavior of the elastic constants have been found in the vicinity of the magnetic phase transition. Measurements under applied magnetic field, both isothermal and variable temperature, show that the value of the elastic constants depends on magnetic order, thus giving evidence for magnetoelastic coupling in this alloy system.

Strain behavior and lattice dynamics in Ni50Mn35In15

“…It has been experimentally shown that in Ni-Mn-X alloys with = X Ga, Al and In the transverse TA 2 phonon branch shows a dip at a particular wave number which softens upon decreasing temperature from the high temperature cubic phase towards a lower-symmetry martensitic phase [7][8][9]. A softening has been further observed in the elastic constants [9][10][11] and is typically found in bcc-based materials which undergo a martensitic transformation. This softening reflects the dynamical instability of the cubic lattice against the shearing of the { } 1 1 0 planes along the <1 1 0> directions.…”

“…Together with the premartensitic transition found in some of the Ni-Mn-Ga alloys, the softening is a pretransitional effect of the martensitic transition [12]. Additional evidence of magnetoelastic coupling has been provided by an enhancement of the anomalous phonon softening accompanying the ferromagnetic (FM) ordering [7] and by the change in the elastic constants upon application of a magnetic field [9,11,13,14]. More generally, softening (or stiffening) is a consequence of coupling between the driving order parameter(s) for a phase transition and strain, which means that observed variations of elastic constants should provide insights into both strain relaxational behavior and the underlying lattice dynamics of Ni-Mn-based Heusler compounds that undergo a martensitic transformation.…”

Lattice dynamics in magnetic superelastic Ni-Mn-In alloys: Neutron scattering and ultrasonic experiments

“…[10][11][12][13][14][15] The temperature dependence of the energy of the anomalous phonon parallels that of the elastic constant CЈ = ͑C 11 − C 12 ͒ / 2, which also softens with decreasing temperature. [16][17][18][19] The softening observed both with neutron scattering and ultrasonic methods is typical for bcc-based solids which undergo martensitic transformations and reflects the dynamical instability of the cubic lattice against shearing of ͕110͖ planes along the ͗110͘ directions. 20 In addition, significant magnetoelastic coupling exists in these systems as evidenced by the enhancement of the anomalous phonon softening when the sample orders ferromagnetically 12,13 and by the change in the elastic constants when a magnetic field is applied.…”

“…20 In addition, significant magnetoelastic coupling exists in these systems as evidenced by the enhancement of the anomalous phonon softening when the sample orders ferromagnetically 12,13 and by the change in the elastic constants when a magnetic field is applied. 19,21 The study of the lattice dynamics of a broader class of Ni-Mn-based compounds is important for a deeper understanding of the physical mechanisms behind the multifunctional properties of martensitic Heusler alloys. Therefore, much effort has been devoted in recent years to extend the study of the lattice dynamics to alloys other than Ni-Mn-Ga and Ni-Mn-Al by means of first-principles calculations.…”

Structural-induced antiferromagnetism in Mn-based full Heusler alloys: The case of Ni2MnAl

“…11 In its stoichiometric concentration Ni 2 MnAl is structurally stable down to low temperatures and at its slightly offstoichiometric composition it presents a high-temperature martensitic phase transition while its mechanical properties are superior to Ni 2 MnGa. 12 Ni 2 MnAl in the B2 phase, where the Ni atoms form a cubic lattice while Mn and Al atoms occupy the other sites randomly ͑for a discussion of the structure see later in the text͒, is a conical antiferromagnet 13 and in the perfectly ordered L2 1 structure evidence for a FM ordering exist from calorimetric measurements. 14 In 2002 Acet and collaborators studied single crystals of Ni 2 MnAl using different annealing temperatures.…”