Magnetic-Field-Induced Effects in Martensitic Heusler-Based Magnetic Shape Memory Alloys

Large magnetocaloric effects in magnetic intermetallics: First-principles and Monte Carlo studies

“…Figure 1 shows the intersection of structural and magnetic phase transitions in the phase diagrams of Ni-Mn-Ga and Ni-Mn-In as a function of the valence electron concentration [20,21]. The ab initio calculations in combination with Monte Carlo simulations reproduce fairly well the experimental phase diagrams, which have been discussed in [3]. [3].…”

“…The ab initio calculations in combination with Monte Carlo simulations reproduce fairly well the experimental phase diagrams, which have been discussed in [3]. [3]. Dark lines (blue, indigo) mark martensitic L2 1 -L1 0 transformation temperatures (from ab initio total energy differences between austenite and martensite [20,21]) and Curie temperatures (from Monte Carlo simulations using ab initio magnetic exchange coupling constants [20,21]), respectively.…”

“…With magnetism as additional degree of freedom, magnetic shape memory Heusler alloys have been found with large reversible deformations under the application or removal of a magnetic field [3]. The strong coupling between magnetism and structure leads to a first order magnetostructural transition with different magnetization of austenite and martensite because of different magnetocrystalline anisotropy and different magnetic exchange coupling constants.…”

Ab initiostudy of Ni2MnGa under shear deformation

“…The MFIS is a consequence of the coupling between the ferromagnetic microstructure and ferroelastic martensite microstructure, which results in a reorientation of martensite twins and the giant strain. Large magneto-crystalline anisotropy and high mobility of martensite twin boundaries are important factors enabling the MFIS [2][3][4][5]. From an atomistic point of view, the reorientation of twins is characterized by a diffusionless and completely reversible change of the crystal structure orientation from one martensite twin variant to another.…”

“…While near stoichiometric Ni 2 MnGa shows cubic L2 1 symmetry in the austenitic phase, the structure of martensitic phase depending on temperature and exact composition are referred as (pseudo-)tetragonal or orthorhombic and can exhibit a modulation. The modulation means a shuffle of (110) planes of L2 1 structure in [1][2][3][4][5][6][7][8][9][10] direction with different periodicity [6]. Modulation with a periodicity of ten lattice planes (10M) or even fourteen lattice planes (14M) has been reported for structures with c/a < 1, which exhibits the MFIS of 6% [7,8] or 10%, respectively [9].…”