Giant electronic polarization induced by a helical spin order in SrMn ₇ O ₁₂ : First-principles calculations

Abstract

Through first-principles density functional calculations, the magnetic ground state and electronic structure of mixed-valent manganite SrMn7O12 in the rhombohedral symmetry are investigated in detail. Our calculations show clearly that the possible magnetic ground state accommodates a particular helical spin order responsible for the insulating state in SrMn7O12. The giant ferroelectric polarization is revealed, which is almost purely from the electronic contribution rather than the ionic displacements and is closely related to the magnetism. The influence of the on-site Coulomb interaction and spin-orbit coupling on the electronic structure and multiferroicity is also discussed. The present results suggest that SrMn7O12 is a promising multiferroic candidate with desirable properties.

High-Pressure Synthesis, Crystal Structures, and Properties of CdMn7O12 and SrMn7O12 Perovskites

“…The absence of sharp dielectric anomalies in CdMn 7 O 12 (at 0 Oe), SrMn 7 O 12 (at 0 and 90 kOe), and SrMn 6.5 Fe 0.5 O 12 (at 0 and 90 kOe) is in agreement with our conclusion that the measured electric current is extrinsic. We can rule out a possibility that intrinsic pyrocurrent is overlapped and hidden by significant extrinsic effects because (i) large polarization (with resultant pyrocurrent comparable with the measured TSC current) is expected in CdMn 7 O 12 and SrMn 7 O 12 by analogy with CaMn 7 O 12 and from first-principle calculations, (ii) we found weak but sharp dielectric anomalies and sharp pyrocurrent at T N2 in PbMn 7 O 12 even with small intrinsic pyrocurrent overlapping with similar TSC current, and (iii) intrinsic pyrocurrent overlapping with significant TSC current was observed in other multiferroics . Therefore, theoretical predictions of ref for SrMn 7 O 12 about its large polarization have not been confirmed by our results.…”

“…We can rule out a possibility that intrinsic pyrocurrent is overlapped and hidden by significant extrinsic effects because (i) large polarization (with resultant pyrocurrent comparable with the measured TSC current) is expected in CdMn 7 O 12 and SrMn 7 O 12 by analogy with CaMn 7 O 12 and from first-principle calculations, (ii) we found weak but sharp dielectric anomalies and sharp pyrocurrent at T N2 in PbMn 7 O 12 even with small intrinsic pyrocurrent overlapping with similar TSC current, and (iii) intrinsic pyrocurrent overlapping with significant TSC current was observed in other multiferroics . Therefore, theoretical predictions of ref for SrMn 7 O 12 about its large polarization have not been confirmed by our results. However, we should mention that no dielectric anomalies were found at T N1 and T N2 in CaMn 7 O 12 (Figure S12) ,,, despite the reported large polarization values (obtained by pyroelectric current measurements in all cases), and in improper ferroelectrics, weak dielectric anomalies are often observed even with large polarization values (e.g., 3 R -AgFeO 2 ), or no dielectric peaks are detected with small polarization values (e.g., 2 H -AgFeO 2 ) .…”

“…In CaMn 7 O 12 , two magnetic transitions occur at T N1 = 90 K, to a long-range helical antiferromagnetic (AFM) order with the emergence of giant ferroelectricity of about 2870 μC/m 2 , and at T N2 = 48 K. Structural and physical properties of its analogues, CdMn 7 O 12 and SrMn 7 O 12 , have not been investigated yet, probably because they can only be prepared at HP-HT conditions. Only one theoretical work appeared recently about SrMn 7 O 12 predicting a giant electronic polarization . In PbMn 7 O 12 , one magnetic transition was found at 68 K without any dielectric anomalies; and no information about ferroelectric polarization was reported …”

Helical magnetism in Sr-doped CaMn7O12 films

“…The out-of-plane 2θ−θ XRD patterns in Figure 1(a [25,26,[34][35][36]. Figure 1(b) shows the reciprocal space maps around the 103 peak of the Ca [22,37,38] and Ca 1-…”

Multiferroic materials and magnetoelectric physics: symmetry, entanglement, excitation, and topology

“…CaMn 7 O 12 is the first multiferroic member of the quadruple perovskite family but definitely not the last one. A recent calculation predicted its sister system SrMn 7 O 12 to be multiferroic [195]. Following experiment observed the pyroelectricity, but it was doubted due to the extrinsic contribution from high leakage [196].…”