Valence states and metamagnetic phase transition in partially $B$-site-disordered perovskite $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$

The valence states of transition metals were studied by measuring the x-ray absorption spectra at both $\mathrm{Mn}{L}_{2,3}$ and $\mathrm{Co}{L}_{2,3}$ edges of partially $B$-site-disordered perovskite $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$. By comparison with analogous spectra in various Co- and Mn-based compounds, the divalent state of the Co ions and the tetravalent state of the Mn ions were established analogous to ${\mathrm{Mn}}^{4+}∕{\mathrm{Co}}^{2+}$ charge ordering found by Dass and Goodenough [Phys. Rev. B 67, 014401 (2003)] in $\mathrm{La}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$. The specific heat and magnetic susceptibility data indicate the formation of the magnetically ordered state at $T_C\sim 120\mathrm{K}$. The first-order metamagnetic transitions seen in $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ at $T<T_C$ suggest the existence of antiferromagnetic and/or paramagnetic clusters embedded into the ferromagnetic matrix.

Figure 1

(Color online) The $\mathrm{Co}{L}_{2,3}$ XAS spectra of $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ and the relevant spectra of CoO $\left({\mathrm{Co}}^{2+}\right)$, $\mathrm{Eu}\mathrm{Co}{\mathrm{O}}_3$ (${\mathrm{Co}}^{3+}$ low-spin state), and ${\mathrm{Sr}}_2\mathrm{Co}{\mathrm{O}}_3\mathrm{Cl}$ (${\mathrm{Co}}^{3+}$ high-spin state).

Figure 2

(Color online) The $\mathrm{Mn}{L}_{2,3}$ XAS spectra of $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ and the relevant spectra of MnO $\left({\mathrm{Mn}}^{2+}\right)$, $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ $\left({\mathrm{Mn}}^{3+}\right)$, and $\mathrm{Sr}\mathrm{Mn}{\mathrm{O}}_3$ $\left({\mathrm{Mn}}^{4+}\right)$.

Figure 3

The temperature dependence of the specific heat of $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$.

Figure 4

(Color online) The temperature dependences of the reduced magnetization of $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ measured in the FC mode in various magnetic fields. The inset represents the temperature dependence of the inverse magnetic susceptibility in the paramagnetic state taken at $0.1\mathrm{T}$. The straight line is the Curie–Weiss law.

Figure 5

(Color online) The temperature dependences of the reduced magnetization of $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ taken after cooling in either positive or negative magnetic field $\pm {10}^{-4}\mathrm{T}$.

Figure 6

The hysteresis loop in $\mathrm{Eu}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_3$ measured at $60\mathrm{K}$ after cooling at ${10}^{-3}\mathrm{T}$.