Kondo screening and beyond: An x-ray absorption and dichroism study ofCePt5/Pt(111)

Abstract

We use x-ray absorption spectroscopy as well as its linear and circular magnetic dichroisms to characterize relevant interactions and energy scales in the surface intermetallic CePt5/Pt(111). The experiments provide insight into crystal field splitting, effective paramagnetic moments, their Kondo screening and mutual interactions and thus into many aspects which typically determine the low temperature behavior of correlated rare earth compounds. Exploiting the tuneability of Ce valence through the thickness dependent epitaxial strain at the CePt5/Pt(111) interface, we are able to systematically investigate the impact of hybridization strength on these interactions. Considerable Kondo screening is indeed observed at all CePt5 thicknesses, and found to be strongest in case of strongest hybridization. While the magnetic response is commensurate with an impurity Kondo scale of TK > ∼ 10 2 K for specimen temperatures T > ∼ 30 K, this is no longer the case at lower temperature. Its detailed study by XMCD at one specific thickness of CePt5 reveals an anomaly of the susceptibility at T * ≈ 25 K instead, which we tentatively associate with the onset of lattice coherence. At lowest temperature we observe paramagnetic saturation with a small Ce 4f saturation magnetization. Within the framework of itinerant 4f electrons, saturation is due to a field induced Lifshitz transition involving a very heavy band with correspondingly small degeneracy temperature of TF ≈ 7 K. This small energy scale results in the persistence of Curie-Weiss behavior across the entire range of experimentally accessible temperatures (T > ∼ 2 K). Our work highlights the potential of magnetic circular dichroism studies in particular for Kondo and heavy fermion materials, which so far has remained largely unexplored.

Absence of Ferromagnetism in VSe2 Caused by Its Charge Density Wave Phase

“…Moreover, simple defects in a host lattice strongly alter both macroscopic and local properties of the system. Magnetic order from disorder has been observed to emerge in Bose condensates upon substitution of non-magnetic ions by spinless impurities [20], Kondo systems [21] and in highly oriented pyrolytic graphite (HOPG) [22], demonstrating that grain boundaries, vacancies and point defects can act as magnetic nuclei in a non-magnetic matrix [23].…”

Structural and electrical characterization of the monolayer Kondo-lattice compound CePt$_6$/Pt(111)

“…From these experiments, the Kondo temperature T K ∼ 100 K and the coherence temperature T * < ∼ 20 K were derived in the multilayer CePt 5 /Pt(111). The thickness-dependent electronic properties of CePt 5 /Pt(111) were also reported with x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and magnetic circular dichroism [38][39][40] . The marked contrast between the bulk and the thin film could be explained by the reduced dimensionality 19 .…”

Crystal fields and Kondo effect: Magnetic susceptibility of Cerium ions in axial crystal fields

“…The new results allow for a quantitative comparison with experimental data with relevance to e.g. CePt5/Pt(111) [13].…”