Evolution of transport and magnetic properties near the ferromagnetic quantum critical point in the series Ca_xSr_1-xRuO ₃

A series of epitaxial films were grown across the solid solution Ca _xSr_1-xRuO₃ in order to pinpoint the ferromagnetic to paramagnetic quantum phase transition in this system and to study the evolution of transport and magnetic properties in its vicinity. The ferromagnetic T_c of SrRuO₃ was found to decrease linearly with Ca doping levels up to 70%. Further doping resulted in the abrupt elimination of ferromagnetic order, and the onset of low temperature (<10 K) non-Fermi-liquid (NFL) resistivity of the form p∝ p₀+AT ^1.5 for samples with x≤0.75≤1.0. The resistivity exponent of 1.5 matches that previously observed for intermetallic alloys (such as MnSi) at their ferromagnetic quantum critical points, indicating the possible universality of this NFL behavior. Field-dependent specific heat measurements on bulk samples at compositions near the quantum phase transition provide additional evidence for NFL behavior (C/T∝log₁₀ T) and show the conditions under which spin fluctuations contribute to the specific heat.