Exploring the magnetic percolation threshold in the improper ferroelectric Sr3Sn2O7 upon Cr and Fe-doping

• Co-doping strategy is successful to introduce magnetic cations into the improper ferroelectric Sr 3 Sn 2 O 7 . • The co-doping preserves structural distortions that permits improper ferroelectricity. • Doping and structural disorder weakens the long-range order of electric dipoles. • Magnetic percolation is not achieved in compounds with 50 % magnetic cations. • Spin-glass like behavior is observed in doped compounds with high concentration of magnetic cations. We examine the effect of Fe and Cr substitutions at the Sn site on the magnetic properties of the hybrid improper ferroelectric Sr 3 Sn 2 O 7 . Upon co-doping with La to preserve the electric charge balance in the unit cell, the Sr 3-x La x Sn 2-x Cr x O 7 , Sr 3-x La x Sn 2-x Fe x O 7 and Sr 2 LaSnFe 1-y Cr y O 7 series can be obtained as single phases up to x = 1 and for all y values. The unit cell volume is isotropically reduced with doping, so that the orthorhombic structure is preserved. However, these substitutions strongly destabilize the ferroelectric order by decreasing the transition temperature, T FE , below room temperature for x ≥ 0.25. La/Cr co-doping is unable to induce long-range magnetic and compositions from this series behave as conventional paramagnetic compounds; although for high doping concentration ( x ≥ 0.5), the significant deviations from the Curie law at low temperatures suggest the onset of antiferromagnetic correlations. In the case of La/Fe co-doping, all samples show strong antiferromagnetic correlations, but a spin glass-like behavior is observed for x ≈ 1 compounds. Finally, no long-range magnetic ordering is observed in La/Cr-Fe co-doped samples, but at the same time an increase in spontaneous magnetization is seen at low temperature, which is associated with the presence of competitive magnetic interactions, in particular the Fe-O-Cr superexchange ferromagnetic interaction. The lack of long-range magnetic order in the investigated series of Cr/Fe-doped Sr 3 Sn 2 O 7, indicates that the critical concentration of magnetic atoms necessary to overcome the magnetic percolation threshold exceeds the 50 % in magnetic cations in these bilayered Ruddlesden-Popper perovskites. Co-doping of Sr 3 Sn 2 O 7 can be performed with La/M(Cr, Fe) up to 50 % of Sn atoms. Ferroelectricity is weakened by this type of co-doping but spontaneous magnetization is observed for high Fe concentrations at low temperature without long-range magnetic ordering.