Effect of negative chemical pressure on the magnetic properties of Cd-doped GdCo2Zn20 single crystals

The negative chemical pressure effect on the magnetic properties of the flux-grown GdCo${}_2$Zn${}_{20-x}$Cd${}_x$ single crystals ($x=0\text{–}1.6$) is studied. The Rietveld refinement of X-ray diffraction (XRD) patterns shows an increase of the lattice parameter. This is consistent with the substitution of Zn with relatively larger ionic size Cd atom and leading expansion of the Zn/Cd cage volume in unit cell. The specific heat, resistivity and magnetic susceptibility measurements show a minor increase of the antiferromagnetic transition temperature ($T_N$), of approximately 0.3 K for $x=1.6$. The Curie–Weiss temperature (${\theta }_{CW}$), extracted from the same analysis, increased from $-0.5\left(5\right)$ K for $x=0$; to $-14\left(1\right)K$ for $x=1.6$. These findings are further compared to the dramatic increase in Curie temperature ($T_C$) observed in Cd-doped GdFe${}_2$Zn₂₀. The minor increase of $T_N$ and ${\theta }_{CW}$ is discussed and explained within the Ruderman–Kittel–Kasuya–Yosida model, where it is argued that the effective exchange coupling between Gd $4f$ moments and the $s$-band conduction electrons is increasing with Cd content.