Microstructure, first-order magnetostructural transition, magnetocaloric properties and exchange bias effect in Ni_45−xBi_xMn₄₄Sn₁₁ alloys

Searching for large magnetocaloric material is the key of applicable magnetic refrigeration. We have systematically investigated the crystal structure, first-order magnetostructural transition, magnetic properties, magnetocaloric effect (MCE) and exchange bias (EB) effect for the Ni_45−xBi_xMn₄₄Sn₁₁ (x = 0, 1, 3 and 5) alloys. The result of X-ray diffraction measured indicates that all compounds have L2₁ cubic structure at room temperature. The martensitic transformation (MT) temperature decreases with the increase in the Bi concentration and magnetic field. A large positive magnetic entropy change ( \({\Delta S}_{{\text{M}}}\) ${\mathrm{\Delta }S}_{\text{M}}$ ) and refrigerant capacity (RC) of all samples were found across MT. The maximum \({\Delta S}_{{\text{M}}}\) ${\mathrm{\Delta }S}_{\text{M}}$ and effective RC are 44.21 J kg⁻¹ K⁻¹ and 125.46 J kg⁻¹ under the magnetic field of 5 T across MT for x = 3, respectively. All the samples exhibit EB effect below the blocking temperature of 60 K, indicating the existence of the magnetic coupled at antiferromagnetic and ferromagnetic interfaces. Under the field-cooled condition of 2 kOe, the maximum EB field (H_E) is 793 Oe at 2 K for x = 3. Our findings demonstrate Ni–Bi–Mn–Sn alloys as one of the promising candidates of MCE material.