Temperature Evolution of Itinerant Ferromagnetism in SrRuO3 Probed by Optical Spectroscopy

TL;DR

This study investigates how the optical conductivity of SrRuO3 changes with temperature, revealing insights into its itinerant ferromagnetism and the persistence of local magnetic moments above the Curie temperature.

Contribution

It provides experimental evidence of temperature-dependent spectral weight shifts and a T^2 dependence below T_c, supporting the involvement of the Stoner mechanism and persistent local moments.

Findings

Spectral weights of charge transfer and d-d transitions vary significantly across T_c.

Optical conductivity shows a T^2 dependence below T_c.

Local spin moments persist above T_c, indicating itinerant ferromagnetism.

Abstract

The temperature ($T$) dependence of the optical conductivity spectra $\sigma(\omega)$ of a single crystal SrRuO$_3$ thin film is studied over a $T$ range from 5 to 450 K. We observed significant $T$ dependence of the spectral weights of the charge transfer and interband $d$-$d$ transitions across the ferromagnetic Curie temperature ($T_c$ ~ 150 K). Such $T$ dependence was attributed to the increase in the Ru spin moment, which is consistent with the results of density functional theory calculations. $T$ scans of $\sigma(\Omega, T)$ at fixed frequencies $\Omega$ reveal a clear $T^2$ dependence below $T_c$, demonstrating that the Stoner mechanism is involved in the evolution of the electronic structure. In addition, $\sigma(\Omega, T)$ continues to evolve at temperatures above $T_c$, indicating that the local spin moment persists in the paramagnetic state. This suggests that SrRuO$_3$ is an intriguing oxide system with itinerant ferromagnetism.