The magnetic, structural, and magnetocaloric properties of Ni₂Mn_0.75Cu_0.25Ga synthesized at high-pressure and high-temperature

High-pressure techniques have been extensively used to explore novel materials with advanced functional properties in the field of materials science for decades. The synthesis of materials under high pressure often results in physical properties not achievable by conventional means. In the present work, polycrystalline Ni₂Mn_0.75Cu_0.25Ga alloys were synthesized at ambient pressure and under high-pressure and high-temperature conditions, and their structural and magnetic properties were investigated. Pressure-induced structural transformation from a monoclinic (14M) to a tetragonal DO₂₂-like crystal structure was observed for the sample synthesized under high-pressure. The magnetic and structural transitions of the alloys formed under high-pressure were found to be coupled in all samples, but their transition temperatures were shifted toward higher temperature by a maximum value of 45 K. A significant expansion of the temperature window where the coupled magnetostructural transition occurs with a reduced maximum magnetic entropy change were observed in high-pressure synthesized samples relative to those synthesized at ambient pressure.