Electron spin resonance across the charge-ordering transition in ${\text{YBaMn}}_2{\text{O}}_6$

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 $T_{\text{CO}}=480\text{K}$ and $T_t=520\text{K}$, 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 $T^{\ast }\approx 410\text{K}$, below which the system can be described as a charge-ordered assembly of ${\text{Mn}}^{3+}$ and ${\text{Mn}}^{4+}$ spins.

Figure 1

(Color online) Crystal structure of ${\text{YBaMn}}_2{\text{O}}_6$. The Y ions (small spheres) and the Ba ions (large spheres) are arranged in alternating layers separated by ${\text{MnO}}_6$ octahedra.

Figure 2

(Color online) Temperature evolution of the ESR spectrum in ${\text{YBaMn}}_2{\text{O}}_6$. Solid lines represent fits using a Lorentzian line shape.

Figure 3

(Color online) Temperature dependence of (a) the ESR spin susceptibility ${\chi }_{\text{ESR}}$ and the dc susceptibility ${\chi }_{\text{dc}}$, (b) the effective $g$ factor, and (c) the ESR linewidth $\Delta H$ in ${\text{YBaMn}}_2{\text{O}}_6$. The lines in the frames (a) and (b) are to guide the eyes and the line in frame (c) is a linear fit. The dashed lines indicate the transition temperatures.

Figure 4

(Color online) Analysis of the ESR parameters in ${\text{YBaMn}}_2{\text{O}}_6$. (a) Temperature dependences of the $g$ factor and of $\Delta \chi ={\chi }_{\text{dc}}-{\chi }_{\text{ESR}}$. (b) Temperature dependence of $\Delta H\chi$ plotted vs the inverse temperature. (c) $\Delta H\left(T\right)$ compared to the temperature dependence of the resistivity on a logarithmic scale.