Nuclear Magnetic Resonance and Magnetization Studies of the Ferromagnetic Ordering Temperature Suppression in Ru Deficient SrRuO3

TL;DR

This study investigates how Ru vacancies in SrRuO3, induced by high-pressure oxygen synthesis, suppress ferromagnetism, using NMR, XAFS, magnetization, and X-ray diffraction to analyze local structure and magnetic properties.

Contribution

It provides detailed local structural and magnetic insights into how Ru vacancies affect ferromagnetic ordering in SrRuO3, combining multiple advanced characterization techniques.

Findings

High-pressure oxygen reduces ferromagnetic transition temperature from 160 K to 90 K.

Ru vacancies are present in high-pressure samples, affecting magnetic properties.

No change in Ru valence between samples despite increased disorder.

Abstract

The synthesis of SrRuO3 under high-pressure oxygen produces a nonstoichiometric form with randomly distributed vacancies on the Ru-sites, along with a significantly reduced ferromagnetic ordering temperature. In order to gain additional insight into the suppression of the ferromagnetism, local studies utilizing 99,101 Ru zero-field spin-echo NMR, and Ru K-edge XAFS, along with complimentary magnetization and x-ray diffraction measurements, have been carried out on samples of SrRuO3 annealed at both ("ambient") atmospheric pressure and "high-pressure" oxygen (600 atm). Consistent with previous work, the NMR spectrum for "ambient" SrRuO3 consists of two well-defined peaks at 64.4 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru isotopes, respectively, and a hyperfine field of 329 kG. Although the magnetization measurements show a lower ferromagnetic ordering temperature for the "high-pressure" oxygen sample (90 K compared to 160 K for the "ambient" sample), the NMR spectrum shows no significant shift in the two peak frequencies. However, the two peaks exhibit considerable broadening, along with structure on both the low and high frequency sides which is believed to be quadrupolar in origin. Analysis of the Ru K-edge XAFS reveals more disorder in the Ru-O bond for the "high-pressure" oxygen sample compared to the "ambient" sample. Furthermore, XANES of Ru K-edge analysis indicates no difference in the valence of Ru between the two samples. The magnetic behavior indicates the existence of some vacancies on the Ru sites for the "high-pressure" oxygen sample.