A Large Inverse Magnetocaloric Effect in Ni49.0Mn37.4Sn13.6 Melt-Spun Ribbons at Room Temperature

Ni49.0Mn37.4Sn13.6 melt spun ribbons (300-900 nm long rectangular bars with 40 nm x 40 nm cross section) exhibit a sharp transition in a thermomagnetic curve from a paramagnetic martensite (M-PM) to a ferromagnetic austenite (A(FM)), with a peak at 299 K when heating at low field such as 50 mT. During a field cooling, the signal does not change much except expanding bit over lower temperatures. The coupled structural and magnetic transitions result in large change in the magnetic entropy which is 6.1 mJg(-1)K(-1) for 2 T field change. The Curie point T-C(A) = 321 K is far above the M-FM phase value 263 K. A 24.2% larger heat-capacity change occurs during cooling in a calorimeter in a considerably irreversible process.