Tuning the hybridization and magnetic ground state of electron and hole doped ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$: An x-ray spectroscopy study

Here we present linear and circular polarized soft x-ray absorption spectroscopy (XAS) data at the Ce $M_{4,5}$ edges of the electron (Ir) and hole-doped (Re) Kondo semiconductor ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$. Both substitutions have a strong impact on the unusual high Néel temperature $T_N=28.5$ K, and also the direction of the ordered moment in case of Ir. The substitution dependence of the linear dichroism is weak thus validating the crystal-field description of ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$ being representative for the Re and Ir substituted compounds. The impact of electron and hole doping on the hybridization between conduction and $4f$ electrons is related to the amount of $f^0$ in the ground state and reduction of x-ray magnetic circular dichroism. A relationship of $cf$-hybridization strength and enhanced $T_N$ is discussed. The direction and doping dependence of the circular dichroism strongly supports the idea of strong Kondo screening along the crystallographic $a$ direction.

Figure 1

(a) Temperature-substitution phase diagram of $\mathrm{Ce}{\left({\mathrm{Os}}_{1-x}{\mathrm{Ir}}_x\right)}_2{\mathrm{Al}}_{10}$ and $\mathrm{Ce}{\left({\mathrm{Os}}_{1-y}{\mathrm{Re}}_y\right)}_2{\mathrm{Al}}_{10}$ showing $T_N$ (red dots) and the magnetic susceptibility at 40 K (blue dots). Data are adapted from Ref. [14]. The red and green regions refer to different magnetically (AF) ordered phases, the length of the red and green arrows symbolizes the size of ordered moment. (b) Integrated $f^0$ intensities obtained from Figs. 3 and 3 in relative units as a function of substitution. The labels strong, interim, and weak refer to the anticipated $cf$-hybridization strength of the respective substitution range.

Figure 2

Experimental linear polarized $M_{5,4}$-edge XAS data of ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$ at 40 K: isotropic spectra $I_{\text{iso}}=1/3I_{E\parallel a}+I_{E\parallel b}+I_{E\parallel c}$) (top, black curve) and polarized data with $E\parallel a$ (red), $E\parallel b$ (green), and $E\parallel c$ (blue). Red arrows point to enlarged regions shown in the insets.

Figure 3

(a) and (b) $f^0$ regions at the Ce $M_{4,5}$ edges (see red arrows in Fig. 2) of isotropic data for ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$ and substitutions with Re and Ir. (c) and (d) Same $f^0$ regions as in (a) and (b) after subtracting a linear background.

Figure 4

(a) Experimental linear dichroism ${\mathrm{LD}}_i$ of Ce $M_5$ edge of all samples for the three crystallographic directions, $i=a,b,c$, with ${\mathrm{LD}}_i=I_{E\parallel i}-I_{\text{iso}}$ and $I_{\text{iso}}=1/3(I_{E\parallel a}+I_{E\parallel b}+I_{E\parallel c}$). By definition $\sum \left(L{D}_i\right)=0$.

Figure 5

(a) Experimental circular polarized $M_{4,5}$-edge XAS data, ${\sigma }_a^{+}$ and ${\sigma }_a^{-}$, for $B=6$ $\mathrm{T}\parallel a$ of (a) paramagnetic, hole doped $\mathrm{Ce}{\left({\mathrm{Os}}_{0.9}{\mathrm{Re}}_{0.1}\right)}_2{\mathrm{Al}}_{10}$ and the CEF-only simulation based on the Strigari et al. parameters [12]. (b) Experimental and (c) calculated (CEF-only) ${\mathrm{MCD}}_i$ with $i=a$, $b$, $c$ of $\mathrm{Ce}{\left({\mathrm{Os}}_{0.9}{\mathrm{Re}}_{0.1}\right)}_2{\mathrm{Al}}_{10}$.

Figure 6

Circular dicroism ${\mathrm{MCD}}_a$ of hole doped (Re, $y=0.1$ and 0.03), pure and electron doped (Ir, $x=0.08$ and 0.15) ${\mathrm{CeOs}}_2{\mathrm{Al}}_{10}$ (colored dots), compared to a CEF-only calculation [12] (red line) at (a) 4 K and (b) in the paramagnetic state at 40 K.