Magnetic properties of CaCu3-xTi4-yFex+yO12 solid solutions: Valence state of iron ions and metamagnetic phase transitions

Abstract

CaCu3-xTi4-yFex+yO12 (1 or 3%) solid solutions were synthesized using a solid state method, while 1 or 3 mas. % of iron (natural abundance of isotopes) was added to the stoichiometric amount of CaO, CuO and TiO oxides. CaCu3-xTi4-y57Fex+yO12 (3%) sample with a higher 57Fe isotope content was synthesized using the same technology for the detailed investigation by the Mӧssbauer spectroscopy. The structural and microstructural characteristics of calcium copper titanate samples were studied by X-ray diffraction, X-ray fluorescence analysis and scanning electron microscopy techniques. The magnetic properties were studied by Mӧssbauer spectroscopy, electron spin resonance and magnetometry methods. Based on all experimental data we can conclude that Fe ions substitute Ti4+ and Cu2+ positions in octahedral and planar oxygen environment, respectively. Such type of substitution leads to the appearance of three types of iron magnetic centers: divalent Fe2+ in the planar environment and trivalent Fe3+ in the symmetrical and distorted octahedral positions that strongly effects to the magnetic properties of the investigated samples. Most unique magnetic properties including the metamagnetic phase transitions are observed in CaCu3-xTi4-yFex+yO12 (3%) sample where both the significant amount of Fe3+ ions in distorted octahedral position together with Fe2+ are present.