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 57 Fe Mossbauer data for the ferrite Ba 3 SbFe 3 Si 2 O 14 with langasite-like crystal structure. The Mossbauer measurements show a two-step magnetic ordering process. Relaxation behavior, for temperatures below T N  ≈ 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* , Mossbauer 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 T N were analyzed assuming the modulation of hyperfine interactions and anisotropy of the magnetic hyperfine field B hf at the 57 Fe nuclei when Fe 3+ magnetic moments rotate with respect to the principal axis of the EFG tensor. The broadening of the electron spin resonance lines upon approaching T N 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  ≥  T 0 , which changes for rather 2D character of magnetic correlations below T 0  ≈ 60 K. Such spin dynamics in Ba 3 SbFe 3 Si 2 O 14 probably triggered by quasi-2D crystal structure and non-trivial helical magnetic structure.