Joan Josep Suñol Martínez

Tailoring of magnetocaloric effect in Ni Ni 45.5Mn 43.0In 11.5 metamagnetic shape memory alloy

We investigate the direct and inverse magnetocaloric effect in Ni 45.5Mn 43.0In 11.5 Heusler alloy ribbons comparing the results obtained for the as-quenched sample with the ones after different annealing procedures. An enhancement and shift of the entropy maximum to near room temperature is observed in all annealed samples. A remarkable magnetocaloric effect is observed in samples with short-time treatment (10 minutes) and at the lowest annealing temperature. We show that the suppressing of uncompensated martensitic transition and thermal hysteresis are both influenced by the heat treatment. Also, an improvement on Curies temperature is observed and, at low magnetic field, it has been risen up to 310K. Our results demonstrate that the martensitic transformation is highly sensitive to the applied magnetic field and also to the annealing treatment, which means that the magnetocaloric effect can be tuned showing different behaviors for each sample

Microstructure and magnetic properties of Ni50 Mn37 Sn13 Heusler alloy ribbons

The Heusler alloy Ni50Mn37Sn13 was successfully produced as ribbon flakes of thickness around 7–10μm melt spinning. Fracture cross section micrographs in the ribbon show the formation of a microcrystalline columnarlike microstructure, with their longer axes perpendicular to the ribbon plane. Phase transition temperatures of the martensite-austenite transformation were found to be MS=218K, Mf=207K, AS=224K, and Af=232K; the thermal hysteresis of the transformation is 15K. Ferromagnetic L21 bcc austenite phase shows a Curie point of 313K, with cell parameter a=0.5971(5)nm at 298K, transforming into a modulated 7M orthorhombic martensite with a=0.6121(7)nm, b=0.6058(8)nm, and c=0.5660(2)nm, at 150K.