Tunable structural and magnetic properties of chemically synthesized dual-phase Co2NiGa nanoparticles

Changhai Wang, Aleksandr A. Levin, Simone Fabbrici, Lucia Nasi, Julie Karel, Jinfeng Qian, Carlos E. Viol Barbosa, Siham Ouardi, Franca Albertini, Walter Schnelle, Horst Borrmann, Gerhard H. Fecher, Claudia Felser

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Abstract

We report the structural and magnetic properties of chemically synthesized dual-phase Co2NiGa shape memory Heusler nanoparticles (NPs). Rietveld analysis of the X-ray diffraction (XRD) data reveals a dual-phase structure for all studied Co2NiGa NPs: the B2 ordered cubic austenite (β) and the tetragonal (γ or martensite β′) phases. We find that the fraction of the tetragonal γ-phase and magnetic properties of NPs consisting of β + γ phases prepared using a heating rate of 0.5 K min-1 can be tuned by varying the Ni-content. Higher saturation magnetization and Curie temperature are observed for Co2NiGa NPs with a higher fraction of the γ-phase. Dual-phase β + γ Co2NiGa NPs exhibit the highest Curie temperature (1153 K) of all known Heusler NPs. Furthermore, the martensite β′-phase is found to coexist with the β-phase for NPs synthesized using a higher heating rate of 2 K min-1. Co2NiGa NPs of mixed β + β′ phase are paramagnetic at room temperature and exhibit low magnetization due to the presence of the martensite phase. High temperature XRD measurements of Co2NiGa NPs with β + β′ phases confirm their irreversible phase transition of the β-phase starting at a temperature of 837 K and the structural stability of the tetragonal β′-phase. The developed new synthetic method makes it possible to fabricate Co2NiGa NPs with structure and properties tailored for high temperature magnetic shape memory devices at the nanoscale.

Original languageEnglish
Pages (from-to)7241-7252
Number of pages12
JournalJournal of Materials Chemistry C
Volume4
Issue number30
DOIs
Publication statusPublished - 14 Aug 2016
Externally publishedYes

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