Magnetic properties and electronic structure of doped multiferroic Y$_{x}$A$_{1-x}$MnO$_{3}$(A=Ca, Sr, Ba)

We report the magnetic properties, X-ray absorption spectroscopy (XAS) on a series of doped multiferroic materials Y$_{x}$A$_{1-x}$MnO$_{3 }$(A=Ca, Sr, Ba). YMnO$_{3}$ when doped by alkaline-earth metal with various ionic sizes, display dramatic changes in magnetic properties as compared with the parent compound. For Ca-doped sample, the antiferromagnetic (AFM) phase transition appears to take place at a much lower temperature (30 K) as compared to that of undoped one (42 K), which could be Mn-rich. On the other hand, when doped with ions of larger size such as Ba and Sr, the AFM temperature decreased only slightly to around 38 K but with significantly smeared transition. By comparing the XAS results to standard manganese oxide powder, YMnO$_{3}$ exhibits the dominant Mn$^{+3}$ characteristics obtained from the standard Mn$_{2}$O$_{3}$ powder. Although, the undoped-YMnO$_{3}$ and Sr-, Ba-doped YMnO$_{3}$ exhibited very similar electronic structure as revealed in the XAS data, the XAS of Ca-doped sample, again, is very different from that of YMnO$_{3}$. It is surprising to observe that Ca-doping has resulted in most significant modifications in the magnetic property and electronic structure of YMnO$_{3}$, since Ca$^{+2}$ is having exactly the same ionic size as that of Y$^{+3}$ and is expected to cause minimal distortion on the lattice.