Heat treatment effect on the evolution of magnetic properties of martensite in magnetic shape memory Ni_(48)Mn_(39.5)Sn_(9.5)Al_3 Heusler alloy ribbons

摘要

The magnetic ground state of martensite in Ni48Mn39.5Sn9.5Al3 ribbons shows considerable complexity and a two stage behavior. Initially, below the blocking temperature it evolves from a superparamagnetic state into a frozen state with a strong ferromagnetic component and it manifests some spin glass like characteristics. The ferromagnetic component is sensitive to thermal treatment, what stems from its susceptibility to variation in the retained ferromagnetic austenite fraction, change in the degree of order as well as the density of ferromagnetic/antiferromagnetic domain interfaces. At temperatures below 80 K, a divergence from linear correspondence to the Almeida-Thouless law signifies that the system enters into a magnetically harder and inhomogeneous state distinguished by exchange bias.