Unconventionally Large Exchange Bias and Cluster Spin Glass State in Mn₂(Ni,Sn) Heusler Alloys Melt Spun Ribbons

Here, we report the structural, microstructural, magnetic, and exchange bias (EB) properties of polycrystalline ribbons of Mn50Ni42.5–xSn7.5+x (x = 0 and 1) Heusler alloys. They exhibit monoclinic structure (7M) at room-temperature (RT). Both the compositions (x = 0, 1) exhibit first-order magneto-structural (martensitic) transition with the martensitic transition temperature (TM) of 389 K for x = 0 and 347 K for x = 1. These TM-values are lower than their bulk counterparts, which is possibly due to the decrease in grains size and atomic order in the later. They exhibit giant exchange bias (EB), with a maximum EB-field (HEB) of 10.2 kOe for x = 0 at 2 K, one of the highest values reported among Mn–Ni based Heusler systems in bulk, thin film, or ribbon form. Frequency dependent ac-susceptibility, scaling law, memory effect, and wait time dependent magnetization relaxation studies confirm the presence of the cluster spin glass (CSG) state. Enhanced exchange coupling between the CSG clusters embedded in a ferrimagnetic matrix is possibly responsible for the giant EB effect in these ribbons.