Role of Ce 4f-conduction band on-site hybridisation in the nature of magnetism in Ce₅MGe₂, where M is d-electron-type metal

ABSTRACT

A combined experimental study and band structure calculations indicate a mixed valence of Ce in the series of Ce${}_{5}M$Ge${}_2$ compounds ($M=$ Ru, Rh, Pd, and Ag), due to strong on-site hybridisation ($V_{fc}$) between Ce $4f$ states and conduction band, which is a reason for their complex magnetic structure. It has been shown that energy $V_{fc}$ is $\sim 50$ meV and does not significantly depend on metal M. In effect, the Curie temperatures of these compounds are very similar ($T_C\sim 14$ K). However, $V_{fc}$ is strongly modified by local atomic environment of Ce ions. The same, exchange interaction between various Ce ions depends on random occupation in the vicinity of Ce sites, which can be cause of spin glass-like state ($T_f$) in the Ce${}_{5}M$Ge${}_2$ series. On the basis of Schrieffer–Wolff transformation, ab initio calculations and x-ray photoelectron spectroscopy (XPS) data, we estimated $J_{fs}$ coupling constants for a Ce${}_{5}M$Ge${}_2$ series, which are dependent on Wyckoff position of Ce and its atomic environment. We argue that various $J_{fs}$ are a reason of spin glass-like state in each compound. For Ce${}_5$RuGe${}_2$, Ce${}_5$RhGe${}_2$ and Ce${}_5$PdGe${}_2$, the interband hybridisation forms a pseudogap in density of states (DOS) at the Fermi level, which could be reason of a Mott variable-range hoping behaviour.

KEYWORDS:

• Magnetic properties
• intermetallic Ce compounds
• electronic structure
• disorder
• hybridisation

Disclosure statement

No potential conflict of interest was reported by the authors.