Magnetic and transport properties of single-crystal ${\mathbf{Ca}}_2{\mathbf{RuO}}_4:$ Relationship to superconducting ${\mathbf{Sr}}_2{\mathbf{RuO}}_4$

${\mathrm{Ca}}_2{\mathrm{RuO}}_4,$ which has the single-layer tetragonal ${\mathrm{K}}_2{\mathrm{NiF}}_4$ structure, shows nonmetallic behavior for $T<\mathrm{}300\mathrm{}$ K unlike its isostructural counterpart, ${\mathrm{Sr}}_2{\mathrm{RuO}}_4,$ which is metallic for all $T<\mathrm{}1300\mathrm{}$ K and which undergoes a superconducting transition temperature below $T=1.35\mathrm{}$ K, possibly with $p-$wave spin pairing. Magnetization, electrical-resistivity, and heat-capacity data for single-crystal ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ are presented. An antiferromagnetic transition is identified at $T_N$=110 K in all samples studied. The easy axis for magnetization is parallel to the $a$ or $b$ axis (in the Ru-O plane). Isothermal magnetization studies in fields to 30 T show a spin reorientation transition for $B$=3.5 T at $T$=105 K and a metamagnetic transition for $T\ll T_N$ at about 9 T. The saturation magnetization even at 30 T, $M_{\mathrm{sat}}\approx 0.4{\mu }_B/$Ru, is less than expected for the Ru $S=1\mathrm{}$ moment ${(M}_{\mathrm{sat}}\approx 2.0{\mu }_B/$Ru). The electrical resistivity, $\rho \mathrm{}\left(T\right),$ increases with decreasing temperature by eight orders of magnitude for 70<$T$<300 K and fits a variable-range hopping model including correlations. The magnetoresistivity below $T_N$ shows some dependence on spin orientation. In contrast to all the other Sr and Ca-based ruthenates, ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ has a relatively small low-temperature electronic specific-heat coefficient (γ=4 mJ/mole ${\mathrm{K}}^2),$ and unlike them, ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ shows no anomaly in either $\rho \mathrm{}\left(T\right)\mathrm{}$ or $d\rho \mathrm{}\left(T\right)/dT$ at $T_N.$ Some magnetization results are presented for lightly Sr-doped ${\mathrm{Ca}}_2{\mathrm{RuO}}_4.$ The data are contrasted with those of metallic ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and discussed in terms of the weak spin disorder scattering in ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ compared to the very strong coupling in the other Sr- and Ca-based ruthenates.