Electron spin resonance across the charge-ordering transition inYBaMn2O6

Abstract

We investigated the metal-ordered manganite system ${\text{YBaMn}}_{2}{\text{O}}_{6}$ using electron spin resonance (ESR) in the paramagnetic regime across the charge ordering and structural phase transition at ${T}_{\text{CO}}=480\text{ }\text{K}$ and ${T}_{t}=520\text{ }\text{K}$, respectively. All ESR parameters exhibit jumplike changes at ${T}_{t}$ while the charge ordering at ${T}_{\text{CO}}$ manifests itself only as a weak and broad anomaly. Above ${T}_{t}$ the ESR spin susceptibility is reduced with respect to the dc susceptibility, indicating that only the ${t}_{2g}$-core spins of Mn ions contribute to the resonance absorption. The contribution of the ${e}_{g}$ spins is suppressed by the time scale of the polaronic hopping process of the ${e}_{g}$ electrons. The linewidth in this regime is reminiscent of a Korringa-type relaxation behavior. In this picture the ESR properties below ${T}_{t}$ are dominated by the slowing down of the polaronic hopping process. The charge fluctuations persist down to the temperature ${T}^{\ensuremath{\ast}}\ensuremath{\approx}410\text{ }\text{K}$, below which the system can be described as a charge-ordered assembly of ${\text{Mn}}^{3+}$ and ${\text{Mn}}^{4+}$ spins.