Correlation of electronic structure and martensitic transition in epitaxialNi2MnGafilms

Abstract

We investigate the martensitic transition of single crystalline Ni 2 MnGa͑110͒ /Al 2 O 3 ͑1120͒ and Ni 2 MnGa͑100͒ /MgO͑100͒ films using magnetometry, x-ray diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism. The martensitic transition from the cubic austenite phase to the low symmetry martensite phase depends strongly on the chosen substrate. For ͑110͒ oriented films on Al 2 O 3 , the martensitic phase is significantly more stable than for the ͑100͒ oriented films on MgO. A remarkable change of the Ni x-ray absorption spectra occurs at the transition, indicating specific changes of the electronic structure. The observed changes are in agreement with theoretical predictions. The orbital to spin momentum ratio of the Ni moment increases significantly on entering the martensite state, thus explaining the macroscopic increase of magnetic anisotropy.

Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

“…In thin films of shape memory alloys with suitable sputtering parameters sharp transitions have also been observed, as reported for Ni-Mn-Ga thin films. 32 The M s in all the films were found to be above RT which is a good signature to use them for RT applications.…”

Magnetic-Field-Induced Reorientation in Single Crystalline Ni-Mn-Ga Foil Actuators

“…Intense research currently focuses on the fabrication of epitaxial FSMA films. However, magnetically induced reorientation has been reported only in a few cases [7][8][9][10]. In order to achieve magneto-strain effects similar to bulk materials, free-standing films with improved crystallinity and microstructures are demanded.…”

Structural and magnetic properties of Ni-Mn-Ga films sputter-deposited on cube-textured polycrystalline substrate

“…The substrate nature and its temperature during deposition are seemingly the main factors determining whether single crystalline or textured polycrystalline state of film is formed. It was found that Ni-Mn-Ga films deposited at room temperature on the alumina ceramic [4], Mo foil [2,3,9], MgO(100) [6] or Si(100) [7] wafers are polycrystalline and exhibit predominantly 220 fiber texture after subsequent heat-treatment at 1070K, whereas these films demonstrated an epitaxial growth during the deposition on heated single crystalline substrates such as Al 2 O 3 (11-20) [5], MgO(100) [5,8,12] or SrTiO 3 (100) [10]. The Ni-Mn-Ga/substrate thin film composites, where the substrate is a micrometer-sized thin metallic foil are promising materials for microactuator applications [2].…”

“…Properties of Ni-Mn-Ga films depend very much on the substrate nature, surface roughness, film thickness and technological details of their production. The transformation behavior and magnetic characteristics of these films are controlled by crystallography, substructure and residual stress [1][2][3][4][5][6][7][8][9][10][11][12]. The substrate nature and its temperature during deposition are seemingly the main factors determining whether single crystalline or textured polycrystalline state of film is formed.…”

“…Thin film technology of these materials is currently under development in order to extend their functionality to the submicron scale [1][2][3][4][5][6][7][8][9][10][11][12]. Properties of Ni-Mn-Ga films depend very much on the substrate nature, surface roughness, film thickness and technological details of their production.…”