Magnetic hyperfine interactions in a sawtooth chain iron oxoselenite Fe2O(SeO3)2: Experimental and theoretical Investigation

Abstract

The iron oxoselenite Fe2O(SeO3)2 hosts unique tilted saw-tooth chains of vertex-sharing iron triangles. It experiences long-range magnetic order below TN ≈ 105 K characterized by a sharp dichotomy in zero-field-cooled and field-cooled behavior (T < TN). The spin-flop transition at low temperatures, BSF = 5.5 T at T = 2 K, suggests the predominance of antiferromagnetic interactions. The 57Fe Mössbauer spectra at T » TN confirm the presence of three non-equivalent crystal sites for high-spin Fe3+ ions. Below TN, the well-resolved Zeeman patterns demonstrate a commensurate magnetic ordering in iron sublattices. The anomalously low value of the saturation hyperfine fields Bhf,Fei at 57Fe nuclei is discussed in terms of the spin reduction (<ΔS> ≈ 0.31), which results from a spin-wave treatment. The mean-field analysis of the temperature evolution of the fields Bhf,Fei(T) allowed evaluation of exchange interactions between different iron sublattices. A spin relaxation behavior of Fe2O(SeO3)2 in the temperature range T* < T < TN (T* ≈ 90 K), which is characteristic for frustrated systems, was shown by the Mössbauer measurements. Density functional theory (DFT) calculations provide the values of exchange parameters within and between the saw-tooth chains.