Hyperfine interaction and electronic spin fluctuation study on Sr$_{2-x}$La$_x$FeCoO$_6$ (x = 0, 1, 2) by high-resolution back-scattering neutron spectroscopy

TL;DR

This study uses high-resolution neutron spectroscopy to investigate hyperfine interactions and spin fluctuations in Sr$_{2-x}$La$_x$FeCoO$_6$, revealing distinct magnetic behaviors across different compositions.

Contribution

It is the first to apply high-resolution inelastic neutron scattering to study hyperfine interactions in these complex magnetic systems, especially in disordered magnetic glasses.

Findings

Clear inelastic signals in magnetic glassy systems indicating hyperfine fields.

No hyperfine signal in magnetically ordered La$_2$FeCoO$_6$, suggesting negligible hyperfine fields.

Observation of electronic spin fluctuations from Fe and Co in disordered magnetic systems.

Abstract

The study of hyperfine interaction by high-resolution inelastic neutron scattering is not very well known compared to the other competing techniques viz. NMR, M\"ossbauer, PACS etc. Also the study is limited mostly to magnetically ordered systems. Here we report such study on Sr$_{2-x}$La$_x$FeCoO$_6$ (x = 0, 1, 2) of which first (Sr$_2$FeCoO$_6$ with x = 0) has a canonical spin spin glass, the second (SrLaFeCoO$_6$ with x = 1) has a so-called magnetic glass and the third (La$_2$FeCoO$_6$ with x = 2) has a magnetically ordered ground state. Our present study revealed clear inelastic signal for SrLaFeCoO$_6$, possibly also inelastic signal for Sr$_2$FeCoO$_6$ below the spin freezing temperatures $T_{sf}$ but no inelastic signal at all for for the magnetically ordered La$_2$FeCoO$_6$ in the neutron scattering spectra. The broadened inelastic signals observed suggest hyperfine field distribution in the two disordered magnetic glassy systems and no signal for the third compound suggests no or very small hyperfine field at the Co nucleus due to Co electronic moment. For the two magnetic glassy system apart from the hyperfine signal due only to Co, we also observed electronic spin fluctuations probably from both Fe and Co electronic moments. \end{abstract}