Element-specific magnetic behavior in ternary MnCoNi multi-principal element alloy

Multi-principal element alloys (MPEAs) exhibit exceptional mechanical properties compared to those of conventional alloys. Recent investigations have revealed their novel magnetic behavior, including spin-glass, ferromagnetic, and superparamagnetic phases. First-principles calculations on equiatomic 3d transition-metal MPEAs suggest that magnetic interactions are closely linked to atomic ordering and reason for superior mechanical properties. In this study, we investigated magnetic properties of MnCoNi thin films as a function of Mn concentration. With increasing Mn content, the films evolve from a predominantly ferromagnetic state in Mn_0.25Co_0.375Ni_o.375, to a mixed state with signatures of both spin-glass and ferromagnetic phases in Mn_0.33Co_0.33Ni_0.33. Finally, a ferrimagnetic state is observed for Mn_0.4Co_0.3Ni_0.3. Using element-specific X-ray magnetic circular dichroism measurements at Advanced Light Source, we show that the magnitude of each element’s moment decreases by roughly a factor of three with increasing Mn concentration. The emergence of the spin-glass phase in Mn_0.33Co_0.33Ni_0.33 and the ferrimagnetic behavior in Mn_0.4Co_0.3Ni_0.3 likely arise from Mn atoms exhibiting both parallel and antiparallel moments to Co and Ni. Overall, our results clearly show that the alignment of magnetic moments is strongly influenced by their local atomic environment and composition of the MPEA.