Valence-instabilibty-driven large magnetostriction in CeCo${1-x}$Fe$x$Si as antiferromagnetic order is suppressed

A strong magnetoelastic effect is observed in the CeCo$_{1-x}$Fe$_x$Si alloys. The strength of the magnetostrictive effect is deeply affected by moderate changes in the iron content $x$. The average low-temperature linear magnetostriction observed at low Fe concentrations ($x \approx$ 0.15) is increased by an order of magnitude ($\frac {\Delta L}{L} \left(16 T,2 K\right) \approx$ 3$\times$10$^{-3}$) around the critical concentration $x_c \approx$ 0.23 at which the long-range antiferromagnetic order vanishes. Upon increasing doping through the nonmagnetic region ($x > x_c$), the magnetostriction strength weakens again. The interplay between magnetic order and the Kondo screening appears to cause an enhanced valence susceptibility slightly changing the Ce ions valence, ultimately triggering the large magnetostriction observed around the critical concentration. Previous studies of the evolution of the lattice parameters with x as well as magnetization and x-ray absorption spectroscopy measurements support this hypothesis.