The nature of the first-order ferromagnetic transition in binary CeIn${}_2$ alloy is investigated by muon spin rotation ($\mu$SR) measurements and chemical substitution of Ce by La in the La${}_{1-x}$Ce${}_x$In${}_2$ ($0.9⩽x⩽1.0$) series of alloys. Below 22 K, the analysis of $\mu$SR spectra shows two spin precession frequencies associated with the local field at the muon site created by the surrounding ferromagnetic ordered magnetic moments. These frequencies abruptly disappear above $T_C$, indicating the first-order character of this transition, as previously reported. For temperatures between 22 and 24 K, the shape of the $\mu$SR spectra indicates the existence of an additional magnetic phase with features of an incommensurate magnetic structure. The presence of this magnetic phase is supported by dc(ac)-magnetic susceptibility and specific-heat results obtained on chemical diluted samples, which also show a magnetic contribution above the ferromagnetic transition. The combined analysis of these results clarifies the first-order character of the ferromagnetic transition in CeIn${}_2$, based on the existence of an intermediate magnetic phase between the paramagnetic and ferromagnetic states.

• Received 8 April 2011

DOI:https://doi.org/10.1103/PhysRevB.84.024403