Thermal, magnetic, and transport properties of single-crystal Sr1−xCaxRuO3 (0<~x<~1.0)

Abstract

${\mathrm{SrRuO}}_3$ is a highly correlated, narrow $d$-band metal which undergoes a ferromagnetic transition at $T_c=165\mathrm{}\mathrm{K}.$ ${\mathrm{CaRuO}}_3,$ which is also a highly correlated metal, has the same crystal structure, comparable electrical resistivity and similar effective Ru moment, but it remains paramagnetic at least down to 1 K. High- and low-field magnetization and susceptibility, thermoremanent magnetization, low-temperature heat capacity, electrical resistivity, and Hall effect measurements are presented on as-grown, untwinned, orthorhombic single-crystal samples of ${\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{RuO}}_3$ for the entire concentration range $0<~x<~\mathrm{1.0.}$ $T_c$ is depressed uniformly with increasing $x,$ all the way to $x=1.0,$ with possible spin-glass-type ordering for $x$ close to 1.0. The critical Sr doping of paramagnetic ${\mathrm{CaRuO}}_3$ required to cause magnetic correlations among the Ru moments is $\cong 1\mathrm{at}.\mathrm{}\%.\mathrm{}$ Magnetization to 7 T shows strong hysteresis for mixed $\mathrm{}(x>\mathrm{}0\mathrm{})\mathrm{}$ crystals only, with evidence for a rotation of the easy magnetic axis out of the $\mathrm{ab}$ plane. Low-temperature magnetization in dc fields to 30 T for $x=0\mathrm{}$ shows a lack of saturation to the full $S=1\mathrm{}$ moment, $2{\mu }_B/\mathrm{Ru}\mathrm{}\mathrm{atom},$ underscoring the itinerant character of the ferromagnetism. Similar data for $x=1.0\mathrm{}$ show it to be a highly exchange enhanced paramagnet, a borderline antiferromagnet or ferromagnet. This is consistent with previous Ru-O in-plane and out-of-plane doping studies. Low-temperature heat capacity $(1<T<\mathrm{}20\mathrm{}\mathrm{K})$ shows that the mass enhancement ($\gamma =29\mathrm{}{\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^2$ and $m^{*}\approx 3$ for $x=0\mathrm{}$) and the Debye temperature (${\Theta }_D=390\mathrm{}\mathrm{K}$ for $x=0\mathrm{}$) are nonmonotonically varying with increasing $x.\mathrm{}$ The large electrical resistivity suggests these materials are “bad” metals, with a mean free path at room temperature $\approx 10\mathrm{A}$ for $x=0.\mathrm{}$ The Hall effect...