Layered (Cu,Fe) oxides of double perovskite structure: Correlation between structural and magnetic-property changes inBaY(Cu0.5

Abstract

In this paper, we report the correlation between the magnetic property and the local structure in BaY͑Cu 0.5 Fe 0.5 ͒ 2 O 5ϩ␦ of the ''0112'' phase containing an unusually large amount of excess oxygen, ␦ of ϳ0.2, when heat treated under a high pressure of 5 GPa. Magnetic susceptibility measurements showed that upon the high-pressure heat treatment, the lower-temperature magnetic transition which had been observed in normal-pressure synthesized, antiferromagnetic BaY͑Cu 0.5 Fe 0.5 ͒ 2 O 5 disappeared and the higher-temperature transition, i.e., the Néel temperature, was lowered. According to a Rietveld analysis based on x-ray-diffraction data and space group P4/mmm, the distinction between Cu and Fe positions along the c axis inside the oxygen pyramid disappeared. Coulometric titrations and Mössbauer spectroscopy measurements strongly suggested the existence of excess oxygen in the yttrium plane. ͓S0163-1829͑98͒03329-3͔

Valence-state mixing and separation inSmBaFe2O5+w

“…The same two components were also identified in the recent studies 18,19 of the Y(Ba,La)(Cu 0.5ϩx Fe 0.5Ϫx ) 2 O 5ϩw double perovskites with trivalent iron. When w decreases below 0.5, signatures of increasing amounts of Fe 2ϩ are found.…”

Interplay between Cu and Fe Valences in BaR(Cu0.5Fe0.5)2O5+δ Double Perovskites with R=Lu, Yb, Y, Eu, Sm, Nd, and Pr

“…Fe> species in the intermediate spin state are not considered here, as the excess oxygen present in the phase indicates that oxidized Fe species should be found. In the earlier reports only one such component was detected (4,5,9) Table 3. The total amount of oxidized Fe in the MoK ssbauer spectra remains roughly the same, whether one is "tting the spectra using one or two components.…”

“…Thus, one is tempted to equate this component with the satellite of Component 1. However, one additional component, seen mainly in high-pressure treated Y-based samples has been reported (5,9). It has an isomer shift typical of Fe> and reaches its saturation "eld of more than 50 T already at 300 K and can thus hardly be considered a satellite of Component 1.…”

“…In general, the AF spectra seldom were completely accounted for using Component 1 only, as an asymmetric broadening of the resonance lines was observed. This was originally handled by introducing a satellite component (1) but later by employing a distribution of the hyper"ne parameter values (2,3,5). We have adopted the former approach in this paper, in order to simplify the "tting.…”

Properties of YBaCuFe1 ? xNixO5 (0 < x ? 0.3) solid solutions

“…According to Ruiz-Aragon [3], the space group of this compound is P 4/ mmm . Magnetic and Mössbauer effect measurements indicate that the Fe ions in YBaCuFeO 5 undergo antiferromagnetic ordering at 460 [1], 446 [2], or 440 K [4]. Detailed studies of the magnetic structure of YBaCuFeO 5 revealed several magnetic phase transitions [3], two of which were identified as paramagnetic antiferromagnetic I (near 475 K) and antiferromagnetic I antiferromagnetic II (near 240 K) transitions.…”