Magnetostructural transition and magnetocaloric effect in thermally annealed Mn0.5Fe0.5NiSi1-xAlx melt- spun ribbons (x= 0.055 and 0.060)

Abstract

The giant magnetocaloric (MC) effect measured in Mn0.5Fe0.5NiSi1-xAlx alloys ( 0.05 < x < 0.07) for a low magnetic field change (|ΔSM|max ~16-24 Jkg-1K-1 at 2 T) [1], and the fact that they are based on cheap and abundant elements motivated the interest on their study. The effect is linked to their first-order martensitic-like magnetostructural transformation (MST) from a high-temperature hexagonal Ni2In-type paramagnetic (PM) phase to a low-temperature orthorhombic TiNiSi-type ferromagnetic (FM) phase which is tunable over wide temperature range by changing the Al content [1,2]. As melt spinning is a rapid solidification technique able to produce alloy ribbon samples with a high chemical homogeneity and may result very appropriate to fabricate these five-elements alloys, we produced Mn0.5Fe0.5NiSi1-xAlx melt-spun ribbons with x=0.055 and 0.060 that were thermally annealed at 1123 K for 4 h; their MST and MC characteristics were studied. RT XRD pattens show that samples are nearly single phase with a major Ni2In-type phase coexisting with a minor amount of the TiNiSi-type one. DSC, M(T)5mT and M(T)2T curves, shown in Fig. 1, denote the occurrence of the MST with a large thermal hysteresis (~ 32 K), the substantial effect of Al-content on the tuning of the MST temperature without a significant change in the magnetization change across the MST which led to similar |DSM(T)|max values (as Fig. 2 shows). The results are discussed and compared with previous data reported in literature for bulk alloys.

References: [1] A. Biswas et al., Acta Mater. 180, 341–348 (2019). [2] C.L. Zhang et al., Appl. Phys. Lett. 105, 242403 (2014).