  In an effort to produce Giant Magnetocaloric effect (GMCE) near room
temperature, in a first ever such study, the austenite transformation
temperature (As) was fine tuned to ferromagnetic Curie temperature (TC) in
Ferromagnetic Shape Memory Alloys (FSMA) and a large GMCE of delta-SM = - 81.75
J/Kg-K was achieved in Ni50Mn18.5Cu6.5Ga25 alloy during reverse martensitic
transformation (heating cycle) for a magnetic field change of 9 T at 302.5 K.
Fine tuning of As with TC was achieved by Cu substitution in Ni50Mn25-xCuxGa25
(0< x < 7.0)-based FSMAs. Characterizations of these alloys were carried out
using Optical and Scanning Electron Microscopy, X-ray Diffraction (XRD),
Differential Scanning Calorimetry (DSC) and DC magnetization measurements.
Addition of Cu to stoichiometric Heusler type Ni2MnGa increases the martensitic
transformation temperatures and decreases TC. Concurrently, DSM increases with
Cu addition and peaks at 6.5 at. % Cu for which there is a virtual overlap
between TC and As. Maximum Refrigerant Capacity (RCP) of 327.01 J/Kg was also
achieved in the heating cycle for 9 T field change at 302.5 K. Corresponding
values for the cooling cycle measurements (measured during forward
transformation) were 30.4 J/Kg-K and 123.52 J/Kg respectively for the same 6.5
at. % Cu sample and same thermo-magnetic conditions.
