Investigation of multifunctional properties of Mn50Ni40−xCoxSn10 (x = 0–6) Heusler alloys

Abstract

A series of Co doped Mn50Ni40−xCoxSn10 (x=0, 1, 2, 2.5, 3, 4 and 6) Heusler alloys has been investigated for their structural, magnetic, magnetocaloric and exchange bias properties. The martensitic transition temperatures are found to decrease with the increase in Co concentration due to the decrease in valence electron concentration (e/a ratio). The Curie temperature of austenite phase increases significantly with increasing Co concentration. A large positive magnetic entropy change (ΔSM) of 8.6 and 10.5J/kgK, for a magnetic field change of 50kOe is observed for x=0 and 1 alloys, and ΔSM values decreases for higher Co concentrations. The relative cooling power shows a monotonic increase with the increase in Co concentration. Large exchange bias fields of 920 Oe and 833 Oe have been observed in the alloys with compositions x=0 and 1, after field cooling in presence of 10kOe. The unidirectional anisotropy arising at the interface between the frustrated and ferromagnetic phases is responsible for the large exchange bias observed in these alloys. With increase in Co, the magnetically frustrated phase diminishes in strength, giving rise to a decrease in the exchange bias effect for larger Co concentration. The exchange bias fields observed for compositions x=0 and 1, in the present case are larger than that reported for Co doped Ni–Mn–Z (Z=Sn, Sb, and Ga) alloys. Temperature and cooling field dependence of the exchange bias field and coercivity have been related to the change in the unidirectional anisotropy. This study shows that an optimum Co doping results in the tuning and enhancement of the multifunctional properties in Mn rich Ni–Mn–Sn alloys.