Spin wave damping arising from phase coexistence below $T_c$ in colossal magnetoresistive La$_{0.7}$Ca$_{0.3}$MnO$_3$

TL;DR

This study investigates the unconventional spin wave damping in La$_{0.7}$Ca$_{0.3}$MnO$_3$, revealing anomalous damping behavior linked to phase coexistence and spatial inhomogeneity below the Curie temperature.

Contribution

It provides clear neutron spectroscopy evidence of increased spin wave damping near the zone boundary, supporting a model of intrinsic phase separation in the material.

Findings

Anomalous increase in spin wave damping near the zone boundary.

Damping depends on excitation energy, rising above 15 meV.

Presence of phase-separated regions approximately 18 Å in size.

Abstract

While the spin dynamics of La$_{0.7}$Ca$_{0.3}$MnO$_3$ in the ferromagnetic phase are known to be unconventional, previous measurements have yielded contradictory results regarding the damping of spin wave excitations. Neutron spectroscopy measurements on a sample with a transition temperature of $T_c$=257 K, higher than most single crystals, unambiguously reveal an anomalous increase in spin wave damping for excitations approaching the Brillouin zone boundary along the [$100$] direction that cannot be explained as an artifact due to a noninteracting phonon branch. Spin waves throughout the ($HK0$) plane display a common trend where the spin wave damping is dependent upon the excitation energy, increasing for energies above roughly 15 meV and reaching a full width at half maximum of at least 20 meV. The results are consistent with a model of intrinsic spatial inhomogeneity with phase separated regions approximately 18 {\AA} in size persisting over a large range of temperatures below $T_c$.