Journal of Metallurgy and Materials Science
Year : 2009, Volume : 51, Issue : 3
First page : ( 197) Last page : ( 203)
Print ISSN : 0972-4257. Online ISSN : 0974-1267.

Magnetic and structural evolution in Ni-rich off-stoichiometric NiMnGa melt spun ribbons

Singh Satnam, Mitra A., Panda A. K.*

National Metallurgical Laboratory, (CSIR), Jamshedpur-831007, India.

*Corresponding Author Email: akpanda@nmlindia.org

Abstract

The investigation is focussed on the magnetic and structural behaviour in a Ni-rich off-stoichiometric NiMnGa alloy. The Ni₅₅Mn₂₂Ga₂₅ (at %) alloy prepared in the form of melt-spun ribbon showed martensitic structure in its as-cast state. Differential scanning calorimetric (DSC) heating and cooling cycles revealed austenitic (A_S=406K) and martensitic (M_S=415K) transformation temperatures respectively which were above room temperature. The Curie temperatures obtained from thermo-magnetic experiments were found to be below these transformation temperatures. The as-spun ribbons revealed low fraction of L2₁ of austenitic phase with a predominant tetragonal (5M) martensite in combination with martensite of higher modulations (7M, orthorhombic). Magnetic coercivity and saturation magnetisation also evidenced the magnetic transitions during ferromagnetic martensite/austenite to paramagnetic austenite.

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Keywords

Ferromagnetic shape memory alloy, Melt spun ribbon, Martensitic transformation, Curie temperature.

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