Spin ordering and hyperfine interactions in langasite-like ferrite Ba3SbFe3Si2O14: 57Fe Mössbauer reinvestigation and ESR measurements

Abstract

The present work reports new analysis and reinterpretation of the 57Fe Mössbauer data for the ferrite Ba3SbFe3Si2O14 with langasite-like crystal structure. The Mössbauer measurements show a two-step magnetic ordering process. Relaxation behavior, for temperatures below TN ≈ 32 K, persisting down to T* ≈ 20 K, indicates the coexistence of the short-range ordering spin clusters within a helically ordering state. Below T*, Mössbauer spectra are consistent with a modulated helical magnetic order, where iron magnetic moments rotate within the (ab) plane with propagation vector along c axis. All experimental spectra at T < TN were analyzed assuming the modulation of hyperfine interactions and anisotropy of the magnetic hyperfine field Bhf at the 57Fe nuclei when Fe3+ magnetic moments rotate with respect to the principal axis of the EFG tensor. The broadening of the electron spin resonance lines upon approaching TN from above was explained in terms of the short-range correlations near magnetic phase transition. The present results evidence a 3D character of magnetic correlations for high-temperatures T ≥ T0, which changes for rather 2D character of magnetic correlations below T0 ≈ 60 K. Such spin dynamics in Ba3SbFe3Si2O14 probably triggered by quasi-2D crystal structure and non-trivial helical magnetic structure.