Electronic structures of (Rb,Ba)Mn[Fe(CN)$_6$] Prussian blue analogue

A$_n$M[M$^{\prime}$(CN)$_6$]$_m$$\cdot$xH$_2$O-type (A: alkali-metal ion; M, M$^{\prime}$: transition-metal ion) Prussian blue analogues (PBAs) have been studied extensively since the discovery of photo-induced spin transition in PBA.\footnote{ O. Sato et al, Science {\bf 272}, 704 (1996).} In the (Rb,Ba)Mn[Fe(CN)$_6$]-type PBAs, antiferromagnetic to ferrimagnetic-like phase transitions were observed below $\sim 5~K$ under magnetic field.\footnote{A. Thakur et al, J. Appl. Phys. {\bf 111}, 063908 (2012).} However, the mechanism of such magnetic transitions is controversial. In this work, we have investigated the electronic structures of (Rb,Ba)Mn[Fe(CN)$_6$] PBAs by employing soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), and charge transfer multiplet (CTM) calculation. The measured XAS and XMCD spectra reveal different bonding characters for Fe and Mn ions, respectively. In the CTM calculation, both the metal-to-ligand charge transfer and the ligand-to-metal charge transfer are found to be necessary. We will discuss on the role of their electronic structures in their phase transitions.