UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2021 Meeting


Section: Solid State Physics and Materials Science


Title:
Microstructure, magnetic and magnetostrictive behaviour in the rapidly quenched off-stoichiometric Ni–Mn–Ga ferromagnetic shape memory alloys


Authors:
Mihaela Sofronie, Felicia Tolea, Monica Enculescu, Iuliana Pasuk, Bogdan Popescu


Affiliation:
National Institute of Materials Physics, Atomistilor 405A, 077125, Magurele-Bucharest, Romania


E-mail
mihsof@infim.ro


Keywords:
ferromagnetic shape memory alloys, martensitic transformation, magnetostriction


Abstract:
The ferromagnetic shape memory alloys (FSMA) applications are related to the well known martensitic transformation (MT), a first-order phase transition in the magnetically ordered domains. The transition takes place between austenite (with disordered B2 or ordered L21 structure) and a seven-layer (7 M), five-layer (5 M) modulated or a non-modulated (L10 tetragonal) martensite structure for Ni-Mn-Ga Heusler type FSMA, depending on composition and thermal history [1]. Rapid quenching techniques like melt-spinning [2] are used even in off-stoichiometric alloys to prevent the undesirable γ-phases, responsible for diminishing the shape memory effect [3]. This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation, magnetic and magnetostrictive properties on the off-stoichiometric Ni51Mn28Ga21 and Ni49Mn31Ga20 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis showed the presence of modulated structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.


References:

[1] N. Lanska, O. Söderberg, A. Sozinov, Y. Ge, K. Ullakko, V.K. Lindroos, Composition and temperature dependence of the crystal structure of Ni–Mn–Ga alloys J. Appl. Phys. 95 (12) (2004) 8074–8078.

[2] J. Gutiérrez, J.M. Barandiarán, P. Lázpita, C. Segúi, E. Cesari, Magnetic properties of a rapidly quenched Ni–Mn–Ga shape memory alloy,Sensors and Actuators A 129 (2006) 163–166 .

[3] F. Tolea, M. Sofronie, AD. Crisan, M. Enculescu, V. Kuncser, M. Valeanu, Effect of thermal treatments on the structural and magnetic transitions in melt-spun Ni-Fe-Ga-(Co) ribbons J. All. Comp, 650 (2015) 664-670.



Acknowledgement:
This work was supported by a grant from the Ministry of Research Innovation and Digitalization, CNCS/CCCDI-UEFISCDI, project number PN-III-P2-2.1-PED-2019-1276, contract no. 324 within PNCDI III.