Griffiths-like phases are connected to disordered magnetic nanostructures. In this study we focus on the Giant Magnetocaloric compound Tb5−xLaxSi2Ge2 with x = 0.075, in which a novel re-entrant cluster-glass state emerges at a characteristic freezing temperature within the Griffiths-like phase – i.e., above the Curie Temperature. We present subtle evidence of spin relaxation and the magnetic structure at the nanoscale to reveal the size of the Griffiths-phase clusters and their connection to magnetic disorder. This is accomplished through DC magnetization and AC susceptibility measurements, including ageing and memory experiments. These techniques are further complemented by Small-Angle Neutron Scattering, which enables us to investigate the nanometric magnetically ordered spin configurations on a mesoscopic length scale. To explain the unusual re-entrant glassy behaviour in the PM state, we propose a phenomenological model based on the formation of ferromagnetic clusters with inter-cluster interactions embedded in a paramagnetic matrix. These findings serve as another experimental reference for the global understanding of disordered magnetic systems.
Link to the open access version of the manuscript:
https://doi.org/10.1016/j.jallcom.2025.182787
