Magnetic exchange interactions and supertransferred hyperfine fields at119Sn probe atoms in CaCu3Mn4O12

The double manganite CaCu${}_{3}$Mn${}_{4}$O${}_{12}$ doped with ${}^{119}$Sn atoms (\ensuremath{\sim}1 at.$%$ with respect to manganese atoms) was studied by use of M\"ossbauer spectroscopy. Formally tetravalent Sn${}^{4+}$ ions substitute for isovalent manganese ions in the octahedral (Mn${}^{4+}$O${}_{6}$) polyhedra. The covalency effects on the magnetic interactions like superexchange in Cu${}^{2+}$-O-Mn${}^{4+}$ and Mn${}^{4+}$-O-Mn${}^{4+}$ bonds and supertransferred hyperfine interactions of the ${}^{119}$Sn probe atoms in the manganite structure are discussed. Using a semiquantitative nearest-neighbor cluster model relating the hyperfine magnetic field on the ${}^{119}$Sn nuclei (${H}_{\mathrm{Sn}}$ $=$ 105 kOe at $T$ $=$ 77 K) to covalency parameters and angle characterizing the Sn-O-$M$ ($M$ $=$ Cu, Mn) bonds, it has been shown how such an analysis of supertransferred hyperfine interactions of tin probe ions can get fruitful information about strength and sign of the superexchange interactions between Mn${}^{4+}$ and Cu${}^{2+}$ magnetic ions. A consistent description of the results in the framework of the Weiss molecular field model considering the specific local environment of tin atoms has made it possible to estimate exchange integrals: ${J}_{\mathrm{CuMn}}$ $=$ \ensuremath{-}51.1 \ifmmode\pm\else\textpm\fi{} 0.3 K and ${J}_{\mathrm{MnMn}}$ $=$ \ensuremath{-}0.6 \ifmmode\pm\else\textpm\fi{} 0.2 K.