Inverse magnetocaloric effect in ferromagnetic Ni-Mn-Sn alloys

• Published in: Nature materials Vol. 4; no. 6; pp. 450 - 454
• Main Authors: Acet, Mehmet, Krenke, Thorsten, Duman, Eyüp, Wassermann, Eberhard F, Moya, Xavier, Mañosa, Lluis, Planes, Antoni
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01-06-2005
• Subjects: Alloys; Alloys - analysis; Alloys - chemistry; Alloys - radiation effects; Cooling; Dose-Response Relationship, Radiation; Electromagnetic Fields; Energy Transfer; Entropy; Intermetallic compounds; Low temperature; Magnetic fields; Magnetics; Manganese - analysis; Manganese - chemistry; Manganese - radiation effects; Materials Testing; Nickel - analysis; Nickel - chemistry; Nickel - radiation effects; Phase transitions; Radiation Dosage; Refrigeration; Temperature; Tin - analysis; Tin - chemistry; Tin - radiation effects
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat1395

The magnetocaloric effect (MCE) in paramagnetic materials has been widely used for attaining very low temperatures by applying a magnetic field isothermally and removing it adiabatically. The effect can also be exploited for room-temperature refrigeration by using giant MCE materials. Here we report on an inverse situation in Ni-Mn-Sn alloys, whereby applying a magnetic field adiabatically, rather than removing it, causes the sample to cool. This has been known to occur in some intermetallic compounds, for which a moderate entropy increase can be induced when a field is applied, thus giving rise to an inverse magnetocaloric effect. However, the entropy change found for some ferromagnetic Ni-Mn-Sn alloys is just as large as that reported for giant MCE materials, but with opposite sign. The giant inverse MCE has its origin in a martensitic phase transformation that modifies the magnetic exchange interactions through the change in the lattice parameters.