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The valence and spin state evolution of Mn and Co on TbMn$_{\rm 1-x}$Co$_{\rmx}$O$_3$ series is precisely determined by means of soft and hard x-rayabsorption spectroscopy (XAS) and K$\beta$ x-ray emission spectroscopy (XES).Our results show the change from Mn$^{3+}$ to Mn$^{4+}$ both high-spin (HS)together with the evolution from Co$^{2+}$ HS to Co$^{3+}$ low-spin (LS) withincreasing $\rm x$. In addition, high energy resolution XAS spectra on the Kpre-edge region are interpreted in terms of the strong charge transfer andhybridization effects along the series. These results correlate well with thespin values of Mn and Co atoms obtained from the K$\beta$ XES data. From thisstudy, we determine that Co enters into the transition metal sublattice ofTbMnO$_3$ as a divalent ion in HS state, destabilizing the Mn long rangemagnetic order since very low doping compositions (${\rm x} \le 0.1$). Samplesin the intermediate composition range ($0.4 \le {\rm x} \le 0.6$) adopt thecrystal structure of a double perovskite with long range ferromagnetic orderingwhich is due to Mn$^{4+}$-O-Co$^{2+}$ superexchange interactions with bothcations in HS configuration. Ferromagnetism vanishes for ${\rm x} \ge 0.7$ dueto the structural disorder that collapses the double perovskite structure. Thespectroscopic techniques reveal the occurrence of Mn$^{4+}$ HS and afluctuating valence state Co$^{2+}$ HS/Co$^{3+}$ LS in this composition range.Disorder and competitive interactions lead to a magnetic glassy behaviour inthese samples.

X-ray absorption and emission spectroscopy study of Mn and Co valence and spin states in TbMn$_{\rm 1-x}$Co$_{\rm x}$O$_3$