Investigation of anomalous thermodynamic and transport properties of Sr_(1-x)Ca_xRuO₃ (x geq 0.8)

Thermodynamic and transport properties of Sr$_{1-x}$Ca$_x$RuO$_3$ with a calcium concentration $x \geq 0.8$ were investigated at low temperatures and in external magnetic field. The investgations revealed a Landau Fermi liquid (LFL) behaviour characterized by specific heat $C/T = const$ and resistivity $\rho\sim T^2$ and an anomalous non-Fermi liquid (NFL) behaviour with $\rho \sim T^{5/3}$ and a quasi-logarithmic increase of $C/T$ with decreasing temperature. The $T$--$x$ and $T$--$B$ phase diagrams which separate both regions were prepared for the investigated materials. Then, the experimental behaviour of $C/T$ and $\rho(T)$ were compared with predictions of the self-consistent renormalization (SCR) theory of spin fluctuations. Within this approach, $C/T(T)$ was well described up to 20 K. The SCR parameters $y_0$, $y_1$ and $T_0$ inferred from specific heat analysis allowed to describe properly $\rho(T)$ up to approximately 5 K. In addition, the resistivity data were analysed within the `hidden Fermi liquid' theory of Anderson, obtaining very good descritption of the experimental behaviour up to about 25 K. An anomalous increase of the $C/T$ ratio already in the LFL region below 2 K in very weak magnetic fields (0.2--0.3 T) was identified as caused by the Schottky anomaly induced by ferromagnetic clusters embodied into the essentially paramagnetic materials.