A crossover from Kondo semiconductor to metallic antiferromagnet with $5d$-electron doping in CeFe$_2$Al$_{10}$

TL;DR

This study investigates how 5d-electron doping in CeFe2Al10 transforms it from a Kondo semiconductor into a metallic antiferromagnet, revealing the suppression of the energy gap and emergence of magnetic order at low temperatures.

Contribution

It provides the first systematic analysis of Ir doping effects on the electronic and magnetic properties of CeFe2Al10, highlighting the decoupling of hybridization gap collapse and magnetic ordering.

Findings

The energy gap is suppressed with Ir doping, leading to a metallic ground state.

Long-range antiferromagnetic order appears below 3.1 K at x=0.15.

The c-f hybridization gap may not be essential for magnetic order in this system.

Abstract

We report a systematic study of the $5d$-electron-doped system Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($0 \leq x \leq 0.15$). With increasing $x$, the orthorhombic $b$~axis decreases slightly while accompanying changes in $a$ and $c$ leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor CeFe$_2$Al$_{10}$, the low-temperature energy gap which is proposed to be a consequence of strong $c \mhyphen f$ hybridization, is suppressed by a small amount of Ir substitution for Fe, and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at $x=$~0.04) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a N\'eel temperature, $T_{\mathrm{N}}$, of 3.1(2)~K for $x = 0.15$. The ordered moment is estimated to be smaller than 0.07(1)~$\mu_\mathrm{B}$/Ce although the trivalent state of Ce is confirmed by Ce L$_3$-edge x-ray absorption near edge spectroscopy. It is suggested that the $c \mhyphen f$ hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce$T_2$Al$_{10}$ ($T$ = Ru and Os), may not be necessary for the onset of magnetic order with a low $T_{\mathrm{N}}$ seen here in Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$.