Exploring a route to induce ferromagnetism on Sr3Sn2O7 by co-doping with non-Jahn-Teller-distorted Mn3+ and La3+ cations

We here explore a route to induce a ferromagnetic ground state on the Ruddlesden-Popper phases Sr 3-x La x Sn 2-x Mn x O 7 replacing Sn by Mn up to x = 1.25. Samples with low Mn concentration (x ≤ 0.1) adopt the polar A2 1 am space group, consistent with previously reported ferroelectric behavior. For higher Mn concentrations (x ≥ 0.25) the samples adopt the centrosymmetric space group Amam due to the suppression of specific rotational modes. X-ray absorption spectroscopy confirmed the presence of a Mn 3+ ion in all samples though it is not Jahn-Teller distorted. An undistorted MnO 6 octahedral local structure is reported instead, with Debye-Waller factors for the Mn-O bond length increasing as Mn content does, due to the disorder induced in the Sn/Mn sublattice and the rising of rumpling distortions (expansion of the perovskite bilayer coupled with shrinkage of the rock salt layer). All the Sr 3-x La x Sn 2-x Mn x O 7 samples exhibit ferromagnetic correlations. While Mn³ ⁺ cations in low Mn-content samples (x ≤ 0.25) agree with spin-only contributions, higher doping levels deviate from this interpretation, possibly due to the enhancement of magnetic interactions. At 5 K, all samples exhibit spontaneous magnetization which increases with Mn content, but the Mn³ ⁺ magnetic sublattice is not fully polarized. Neutron diffraction confirmed the absence of long-range magnetic order and AC susceptibility analysis indicates a cluster-glass magnetic state due to structural disorder and competing interactions. Compared to simple perovskites, our results indicate that the rock salt layer plays a key role in suppressing long-range ferromagnetic order, making it particularly challenging to achieve multiferroic behavior by doping hybrid improper ferroelectrics with magnetic cations. • Mn and La incorporation suppresses the improper ferroelectric mechanism in Sr₃Sn₂O₇. • Mn³ ⁺ is not Jahn-Teller active in this series, favoring ferromagnetic correlations. • Higher Mn content increases disorder and structural rumpling distortions. • Ferromagnetic correlations emerge , but no long-range magnetic order forms. • Rock-salt layers suppress magnetic coherence in bilayered Ruddlesden–Popper structures.