Phase transitions, thermal, electrical, and magnetocaloric properties of Ni50Mn37-xAlxSn13 (x=2, 4) ribbon samples

Abstract The specific heat (CP), thermal diffusivity (η), thermal conductivity (κ), magnetization, resistivity (ρ), and magnetocaloric effect (MCE) were studied in fast-quenched ribbon samples of the Ni50Mn37-xAlxSn13 alloy (x = 2, 4). Anomalies are observed in the form of a jump for the temperature-dependent η(T) and κ(T) near the magnetic and magnetostructural phase transitions, which are associated with critical scattering of heat carriers by distortions of the crystal structure, fluctuations of the order parameter, or structural/magnetic inhomogeneities. The transition to the martensitic phase is found to be accompanied by a sharp increase in the resistivity, suggesting an increase in the electron relaxation rate due to structural distortions inherent in martensite. The value of the magnetoresistive effect at 1.8 T near the martensitic transition reaches ∼40%. The temperature hysteresis was investigated in terms of ρ(T) near TC, which is explained based on the coexistence of the magnetic two-phase state of FM + AFM and the structural magnetic heterogeneity of the samples with dominant austenitic phase. For a sample with x = 2, the electron and phonon components of thermal conductivity were estimated (κph » κe).