Thickness-Dependent Magnetism and Kondo Coherence in Monoclinic CeSb₂ Thin Films

Heavy fermion materials are known to host a rich variety of correlated and magnetic ground states due to the competing Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Reducing the dimensionality of such systems down to the ultrathin limit is an enticing avenue for tuning this competition and potentially engineering new correlated behaviors. Here we discuss thin films of the heavy fermion material CeSb₂ grown via molecular beam epitaxy on MgO (100) substrates. The CeSb₂ films stabilize in a monoclinic structure (space group 12, A2/m) with a compressed c-axis relative to the orthorhombic bulk crystals. We characterize the new structure’s electronic and magneto-transport properties and compare them to those of the bulk material. Signatures of magnetic ordering and Kondo Lattice behavior are identified and tracked as a function of film thickness down to about 4.5 nm. We observe the opposing evolution of the Kondo coherence and RKKY-related temperature scales, accompanied by a crossover in the magnetic ordering of the low-temperature ground state in the thinnest films. Possible interpretations of these results will be discussed, including dimensionality-driven tuning of electron correlation, disorder effects, and thickness dependence of the CeSb₂ band structure.