Ferromagnetic quantum phase transition in Sr$_{1-x}$Ca$_x$RuO$_3$ thin films

TL;DR

This study investigates the ferromagnetic quantum phase transition in Sr$_{1-x}$Ca$_x$RuO$_3$ thin films, revealing a continuous suppression of Curie temperature and changes in electrical resistivity behavior near the critical doping level.

Contribution

It provides detailed experimental evidence of the quantum phase transition in Sr$_{1-x}$Ca$_x$RuO$_3$ thin films, including high-quality sample characterization and low-temperature transport measurements.

Findings

Curie temperature decreases to zero at x≈0.8

Resistivity shows T^2 behavior for x≤0.6

Resistivity shows T^{3/2} behavior for x≥0.7

Abstract

The ferromagnetic quantum phase transition in the perovskite ruthenate Sr$_{1-x}$Ca$_x$RuO$_3$ is studied by low-temperature magnetization and electrical resistivity measurements on thin films. The films were grown epitaxially on SrTiO$_3$ substrates using metalorganic aerosol deposition and characterized by X-ray diffraction and room temperature scanning tunneling microscopy. High residual resistivity ratios of 29 and 16 for $x=0$ and $x=1$, respectively, prove the high quality of the investigated samples. We observe a continuous suppression of the ferromagnetic Curie temperature from $T_C=160$ K at $x=0$ towards $T_C\to 0$ at $x_c\approx 0.8$. The analysis of the electrical resistivity between 2 and 10 K reveals $T^2$ and $T^{3/2}$ behavior at $x\leq 0.6$ and $x\geq 0.7$, respectively. For undoped CaRuO$_3$, the measurement has been extended down to 60 mK, revealing a crossover to $T^2$ behavior around 2 K, which suggests a Fermi-liquid ground state in this system.