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

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 Å in size persisting over a large range of temperatures below $T_c$.

arXiv commentv2: 8 pages, 7 figures v1: 7 pages, 7 figures

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