Magnetic and magneto-functional properties of Mn5Si3 alloy

Recently, metal silicides have attracted renewed attention due to their potential application in microelectronics. Apart from their interesting electronic properties, these materials also show diverse magnetic and magnetofunctional behaviors, including magnetocaloric, anomalous Hall effect, and spin fluctuation. The silicide of nominal composition Mn5Si3 is under active scientific investigation due to its fascinating structural, magnetic, and magnetofunctional behaviors. It crystallizes in a hexagonal D88 type structure (space group P63/mcm) with two distinct crystallographic sites (Mn1 and Mn2) for Mn atoms. A decrease in sample temperature results in two magnetic transitions: paramagnetic to collinear antiferromagnetic (AFM2) phase around 100 K and AFM2 to noncollinear antiferromagnetic phase (AFM1) around 66 K. On the other hand, the appearance of another intermediate noncollinear antiferromagnetic phase (AFM1⸍) has been reported in the presence of an external magnetic field. Apart from these multiple magnetic transitions, two novel features, namely, inverted hysteresis loop (IHL) and thermomagnetic irreversibility, have been observed by dc magnetic measurements. The thermomagnetic and isothermally arrested AFM1⸍ state is playing the pivotal role behind such novel features. To check the robustness of the observed IHL and arrested behavior, the effect of foreign element doping at the Mn-site of Mn5Si3 alloy has been studied. Such study unveils two crucial features: (i) decrease in AFM1⸍ phase fraction with increasing doping concentration; (ii) gradual disappearance of IHL and thermomagnetic irreversibility behavior with increasing doping concentration. In addition, the doping concentration in Mn-site significantly affects the magnetic properties and magneto-functional properties, such as the magnetocaloric effect and magnetoresistance of these alloys. A neutron powder diffraction study has been performed on Ni-doped alloys to understand the impact of doping on the magnetic structures. The magnetic structure is particularly important for this alloy family due to the near-critical values of Mn-Mn distance. Ni-doping decreases the intra-site Mn-Mn distance and increases the inter-site Mn-Mn distance between Mn1 and Mn2 sites. Such change in Mn-Mn distances directly affects the existing exchange interactions and affects the moment size and Mn spin orientation in the Ni-doped alloys. Approaching near a parallel arrangement of Mn moments at the AFM1 phase with increasing Ni-concentration indicates that the Ni- doping prefers the AFM2 phase over the AFM1 phase.