Muon spin relaxation in mixed perovskite (LaAlO$_3$)$_{x}$(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{1-x}$ with $x\simeq 0.3$

TL;DR

This study uses muon spin relaxation measurements to investigate local magnetic environments in a mixed perovskite substrate, revealing muon diffusion behavior influenced by the material's cation distribution.

Contribution

It provides new insights into muon diffusion mechanisms in mixed perovskites and links these behaviors to the cation disorder within the lattice structure.

Findings

Muon depolarization due to nuclear dipole fields observed from 4 K to 270 K.

Gaussian-like muon spin relaxation spectra maintained across the temperature range.

Muon diffusion paths are restricted by cation disorder, affecting local magnetic fields.

Abstract

We report on muon spin relaxation ($\mu^+$SR) measurements in a mixed perovskite compound, (LaAlO$_3$)$_{x}$(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{1-x}$ with $x\simeq 0.3$ (LSAT), which is widely used as a single-crystalline substrate for thin film deposition. In zero applied field (ZF), muon depolarization due to the distribution of nuclear dipole fields was observed in the temperature range from 4 K to 270 K. Interestingly, $\mu^+$SR time spectra in ZF maintained a Gaussian-like feature over the entire range, while the depolarization rate exhibited a monotonic decrease with increasing temperature. This behavior may be attributed to the thermally activated diffusion of muons between a few adjacent sites within a confined space of the angstrom scale, where the motionally averaged local field that each muon experiences can remain non-zero and result in maintaining the Gaussian-like line shape. The spatial distribution of electrostatic potential at lattice interstices evaluated via density functional theory calculations suggests that such a restriction of muon diffusion paths can be caused by the random distribution of cations with different nominal valences in the mixed perovskite lattice.