DESIGN AND DEVELOPMENT OF HEUSLER ALLOYS FOR MAGNETIC REFRIGERATION APPLICATIONS

Cooling systems are used in houses, cars, hospitals, defence systems and many other such areas. However, the gases (chlorofluorocarbons and hydrochlorofluorocarbons) present in today's refrigerant systems are harmful to the environment and cause global warming. Moreover, today's cooling technology is expensive and low efficiency technology. Therefore, new and cost-effective with higher energy efficiencies cooling systems have begun to be developed to eliminate the use of these harmful gases. Among them, magnetic refrigeration has attracted increasing interest in the materials research communities because of its higher cooling efficiency and environmentally friendliness. Full Heusler alloys are magnetic ternary intermetallic compounds with the L2(1)-type crystal structure. Typically, these alloys undergo a low temperature martensitic transformation (austenite <-> martensite), a magnetic transformation (ferromagnetic <-> paramagnetic) and relatively high temperature atomic ordering (order <-> order and order <-> disorder) transformations. After the discovery of the ferromagnetic shape memory (FSM) and giant magnetocaloric effects (GMCE) in Ni-Mn-Ga alloy, Ni-Mn based Heusler alloys have received considerable attention due to their unique magnetic and structural properties. In this present study compositional dependence of structural and magnetic properties of off-stoichiometric Ni-rich Ni-Mn-Ga Heusler alloys have been investigated, in order to determine an alloy composition where a coupled magneto -structural transformation occurs and to measure the MCE near this temperature. Structural and magnetic properties of Ni-Mn-Ga Heusler alloy system were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) measurements.