Title : Composition dependent structural, martensitic and magnetic properties of NiMnCoTi ferromagnetic shape memory alloys
Ni-Mn based ferromagnetic Heusler alloys have gained much attention because they have applications in many areas such as magnetic refrigeration, sensors, magneto-mechanical devices and energy-harvesting devices. In present work we investigate the structural, martensitic and magnetic properties of Mn35+xNi35-xCo15Ti15 (x=0, 1, 2 and 3) alloys using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC) and magnetic measurements. XRD analysis shows two sets of diffraction patters, with increase in values of x: the proportion of cubic B2 type increases while 5M modulated structure decreases. Large endothermic/exothermic peaks with distinct thermal hysteresis in DSC measurement indicate the martensitic/reverse martensitic transformations and martensitic transformation temperature decreases with increase in x. Thermal magnetization (M-T) curves show an abrupt change of magnetization from paramagnetic martensite to ferromagnetic austenite near MT temperature. Isothermal magnetization (M-B) curves for Mn35+xNi35-xCo15Ti15 show that magnetic field can induce the magnetostructural transformation. A magnetic entropy change of 12 is observed at room temperature (290 K) in Mn35+xNi35-xCo15Ti15
Martensitic Transformation, Magnetocaloric effect, Magnetic refrigeration.
- The materials showing martensitic transformation (MT) exhibit various multifunctional phenomena such as magnetocaloric effect (MCE), exchange bias (EB), magnetothermal conductivity (MC) and magnetoresistance (MR). This coupled transition is obtained around the MT temperature.
- The MCE is a magneto-thermodynamic phenomenon in which temperature is changed in the material when exposed to the external-non-constant magnetic field.
- Magnetic refrigeration is a best alternate conventional gas cooling technology, showing many, such as environment friendly, high refrigerant efficiency, low cast, occupying less space, low mechanical vibration, and harmlessness