Tuning electric polarization via exchange striction interaction in CaMn7O12 by Sr-doping

Magnetoelectric (ME) materials displaying magnetically induced polarization have attracted considerable interest due to their potential applications in spintronics and various fast electrically controlled magnetic devices. CaMn₇O₁₂ (CMO) stands out for its giant spin-induced ferroelectric polarization. However, the origin of the induced electric polarization in CMO remains highly controversial and continues to be a subject of ongoing debate. In this paper through room temperature X-ray powder diffraction (XRPD), temperature-dependent magnetization, and thermally stimulated depolarizing current (TSDC) measurements, we provide experimental evidence for a route to tune the magnetically induced polarization by modifying the exchange-striction in CMO via Sr-doping. Our findings demonstrate that the large and broad current density peaks observed near the first magnetic phase transition (T_N1∼90 K) indicate contributions to the TSDC from both extrinsic dipolar thermally stimulated relaxation processes and intrinsic pyroelectric current, the later arising from magnetically induced polarization changes. We suggest that the reduction in induced electric polarization in CMO originates from an increase in the Mn³ ⁺–O–Mn⁴⁺ bond angle due to Sr²⁺ doping, which weakens the exchange-striction interaction. Meanwhile, the Dzyaloshinskii–Moriya (DM) effect determines the direction of the induced electric polarization. Our result sheds light on understanding the intriguing giant-induced polarization in CMO and similar compounds with complex magnetic structures.