Structural behavior and magnetic properties of a Ni–Mn–Ga single crystal across the martensite/austenite two-phase region

Abstract The martensite/austenite two-phase region of a Ni–Mn–Ga single crystal is investigated using different analytical techniques (DSC, SQUID, and XRD) in order to accurately determine the maximum operating temperature for the magnetic shape memory (MSM) effect. It is found that the width Δ T A = A f − A s of the two-phase region and the austenite start temperature A s are significantly affected by the variant structure of the martensite prior transformation. The austenite finish temperature A f remains on the other hand constant. In the multi-variant martensite the width Δ T A measured as large as 20 K, while in the single-variant the width is A s temperature of the single-variant sample, which in turn determines the maximum MSM operating temperature. Magnetic and mechanical properties across the two-phase region were thoroughly investigated. A considerable improvement of the high-temperature MSM properties is demonstrated for the alloy examined in the present work.