Magnetic response and hyperfine magnetic fields at Fe sites in Sr3Fe2MO9 (M= Mo, Te, W, U) double perovskites

L. A. BAUM; SILVANA JACQUELINE STEWART; R. C. MERCADER; G. M. GRENECHE

Hyperfine Interactions

Año: 2004 vol. 156/ p. 157 - 163

0304-3843

We have studied the isostructural series of double-perovskites Sr3Fe2MO9 (M = Mo,Te, W, U) by Mössbauer spectrometry and AC susceptibility measurements. The hyperfine structure of Mössbauer spectra at room temperature is attributed to the presence of high spin state Fe3+ ions sensing both static and fluctuating magnetic hyperfine fields with different relative areas that dependon M. The magnetically split signal – indistinguishable from the background in the Mo compoundspectrum – increases with the Fe-site disorder in the sequence Mo < U < Te < W. The spectraat 77 K demonstrate that the W-perovskite sample is already magnetically fully ordered, while the other three cations suggest ordering temperatures that increase from Te to U to Mo. At 4.2 K all thespectra are completely magnetically split and display hyperfine fields that range from 49 up to 53 T.Coincident with the X-ray and neutron diffraction results, the hyperfine parameters are consistentwith Fe atoms centered in oxygen octahedral units, coordinated to different numbers of M-centered octahedra. The AC susceptibility response is χmax ≈ 3.5 × 10−5 emu/g.Oe for the Mo compound and increases for the W, Te and U compounds with values of χmax1.6 × 10−4, 3.0 × 10−4, and 9.4×10−3 emu/g.Oe, respectively. The out-of-phase component, χ, could only be detected for the U compound. Its frequency dependence displays a shift that denotes a spin-glass-like state arising from the chemical disorder.