Thermodynamic Properties of (Ca,Sr)${}_2$RuO${}_4$ in Magnetic Fields

We have studied the influence of a magnetic field on the thermodynamic properties of Ca${}_{2-x}$Sr${}_x$RuO${}_4$ in the intermediate metallic region with tilt and rotational distortions ($0.2\le x\le 0.5$). We find strong and anisotropic thermal expansion anomalies at low temperatures, which are suppressed and even reversed by a magnetic field. The metamagnetic transition of Ca${}_{1.8}$Sr${}_{0.2}$RuO${}_4$ is accompanied by a large magnetostriction. Furthermore, we observe a strong magnetic-field dependence of $c_p\mathrm{/}T$, that can be explained by magnetic fluctuations.