Giant magnetic-field-induced strain in NiMnGa seven-layered martensitic phase

Abstract

Giant magnetic-field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less than 1 T in NiMnGa orthorhombic seven-layered martensitic phase. The strain proved to be caused by magnetic-field-controlled twin boundary motion. According to an analysis of x-ray diffraction data, the crystal structure of this phase is nearly orthorhombic, having lattice parameters a=0.619 nm, b=0.580 nm, and c=0.553 nm (in cubic parent phase coordinates) at ambient temperature. Seven-layer shuffling-type modulation along the (110)[11̄0]p system was recorded. The results of mechanical tests and magnetic anisotropy property measurements are also reported.

Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In

“…3,4 Giant strains up to 10% have been reported for off-stoichiometric Ni-Mn-Ga single variant crystals with the 14 M modulated martensitic structure. 5 Over the past decade, vast amount of knowledge accumulated on the properties of Ni-Mn-Ga Heusler alloys has enabled to foresee the possibility of employing these alloys in device applications. 6 In applied magnetic fields, the martensitic start temperature M s of Ni-Mn-Ga shifts to higher temperatures along with the other characteristic temperatures such as martensite finish M f , austenite start A s , and austenite finish A f .…”

Martensitic transition and structural modulations in the Heusler alloy Ni2FeGa

“…Among the large number of ferromagnetic Heusler alloys, the intermetallic Ni -Mn-Ga alloy is a typical one undergoing a martensitic transition (MT) at T m , 200 K; which, in our knowledge, could give rise to the maximum magnetic-field-induced strain [5][6][7][8][9][10]. In this kind of materials, experimental and theoretical investigations have been specially focused on the anomalies behavior in the ½110 -TA 2 phonon branch [11], evident structural distortions, corresponding to atomic displacements along k 2 110l direction, was identified in a large temperature range [11,12].…”

Non-Modulated Martensite Microstructure With Internal Nanotwins In Ni-Mn-Ga Alloys

“…It is now widely accepted that the magnetic field induced strain (MFIS) occurs in 10M and 14M modulated martensite structures of Ni-Mn-Ga single crystals [1][2][3]. The microstructure of modulated martensites has been thoroughly studied by x-ray and electron backscatter diffraction (EBSD) techniques revealing a more complex character of twin boundaries than earlier assumed [4][5][6][7].…”

“…From these ingots large single crystal with dimensions 10×10×50 mm 3 were grown by a modified Bridgman method in an induction furnace at a vacuum better than 10 -5 hPa. A boron nitride crucible was used since it is non-reactive to each of the elements used.…”