Effect of Annealing on the Structural and Magnetic Properties of CoNiAl FSMA.

A ferromagnetic shape memory alloy is a very interesting system that has various structural transformation, microstructural phases and magnetic properties, and interplays among them. The system studied here is Co39Ni34Al27 that comprises a mixture of β (body‐centered cubic) and γ (face‐centered cubic) structural phases. Here the β phase is responsible for the FSMA behavior and the γ phase improves the mechanical properties necessary for practical applications. Herein, it is showed through resistivity and magnetization measurements that post‐annealing to a higher temperature significantly alters the ratio of β and γ phases in the system, resulting in increasing the austenite to martensite transition temperature and significantly modifying the magnetic properties. Additionally, it is also shown that the low‐temperature magnetic phase of this FSMA system is a disordered magnetic system. Extensive electrical resistivity measurements in a CoNiAl system show for the first time that low‐temperature ground state is magnetically disordered. However, the higher temperature behavior is dominated by altering the ratio of β and γ phases by varying the annealing conditions, resulting in significant changes in structural transformation and magnetic properties. [ABSTRACT FROM AUTHOR]