Evolution of microstructure, elemental segregation and magnetic order in Ti20Co20Cu20Fe20Ni20 high entropy alloy

Ti20Co20Cu20Fe20Ni20 HEA was prepared by mechanical alloying and consolidated by spark plasma sintering. The microstructural studies including Atom Probe Tomography and evaluation of magnetic properties suggest partitioning of elements into (Fe, Co, Ni)-rich ferromagnetic delta-phase and non-ferromagnetic mu -phase. Owing to large change of magnetic entropy across the Curie temperature of the ferromagnetic phase, the phase separation becomes more prominent and is evident in the form of clustering of ferromagnetic elements. The presence of alternate lamellae of ferromagnetic delta phase and non-ferromagnetic mu -phase in some grains, led to anti- ferromagnetic interactions amongst ferromagnetic delta lamellae resulting from separation by fine scale non- ferromagnetic spacer (mu lamella). Such antiferromagnetic exchange is also in accordance with similar exchange behaviour in Fe/Cu/Fe and Co/Cu/Co multilayers reported earlier. The co-existence of ferromagnetic and antiferromagnetic order leads to presence of exchange bias as evident in the asymmetric shift in the hysteresis loop of the samples along positive field axis.