Thermal annealing effects on the magnetic behavior of Ce2NiSi3

We have investigated the crystallographic, magnetic and thermodynamic properties of the as-cast and annealed Ce2NiSi3 alloys, crystallizing in the AlB2-type hexagonal structure. The DC-magnetic susceptibility data show that the as-cast sample exhibits an antiferromagnetic (AFM) ordering below TN= 3.8 K, whereas the annealed sample shows, at 4.2 K, a magnetic transition of AFM nature and, around 2.5 K, an additional anomaly. The specific heat shows a peak with cmax=7.4J/molK at 3.8 K for the as cast sample, which shifts to lower temperatures when the magnetic field increases, consistent with the antiferromagnetic nature of the transition. On the other hand, in the annealed alloy, the maximum of the specific heat peak reaches 9.3J/molK at 4.2 K, and no additional anomalies were observed. The different magnetic behavior between the as-cast and annealed samples is attributed to thermal effects on the structural disorder of nickel and silicon atoms, as already observed in other isotypic R2TSi3 alloys, where R=U or Ce, and T= transition metal.