Multiferroic properties of CaMn7O12

Abstract

We report that CaMn7O12 is a new magnetic multiferroic material. The appearance of a ferroelectric polarization coinciding with the magnetic phase transition (∼ 90 K) suggests the presence of ferroelectricity induced by magnetism, further confirmed by its strong magnetoelectric response. With respect to other known magnetic multiferroics, CaMn7O12 displays attractive multiferroic properties, such as a high ferroelectric critical temperature and large polarization. More importantly, these results open a new avenue to search for magnetic multiferroics in the catalogue of doped oxides.

Soft vibrational mode associated with incommensurate orbital order in multiferroicCaMn7O12

“…Clear anomalies can be observed at the T N1 = 90 K and T N2 = 48 K magnetic phase transition temperatures, consistent with an earlier report on polycrystalline samples. 20 In contrast, no anomaly can be resolved near T o = 250 K. …”

“…1) prop- agating along the crystallographic c-axis. CaMn 7 O 12 exhibits multiferroic properties below T N1 = 90 K. An unprecedentedly large magnetically induced ferroelectric polarization [20][21][22] arises from a helical magnetic structure due to exchange striction, 22 and it is suggested that the orbital order at higher temperature sets the stage for the helical magnetic structure to be stabilized. 17 These novelties motivated us to study the mechanism for the orbital ordering in CaMn 7 O 12 using Raman spectroscopy, which is sensitive to symmetry breaking via the observation of collective excitations.…”

“…At lower temperatures, CaMn 7 O 12 undergoes two magnetic phase transitions 20,21,26 at T N1 = 90 K and T N2 = 48 K. Since our current study mainly concerns the orbital order, here we refrain from a detailed description of the magnetism in CaMn 7 O 12 , but only mention that (1) the magnetic wave vector q m in the T N2 < T < T N1 phase locks into the orbital-ordering wave vector, q m = q o /2 (Ref. 27), and (2) the orbital order appears to be responsible for the magnetic interactions that lead to the helical magnetic order below T N1 (Ref.…”

Giant Improper Ferroelectricity in the Ferroaxial MagnetCaMn7O12

“…Measurements of polycrystalline samples showed that the development of long-range antiferromagnetic order below T N1 coincides with the onset of a large ferroelectric polarization [7]. In the present study, the electric polarization was measured on our single crystals perpendicular to the natural facets (parallel to the <100> pseudo-cubic axes) and along the three-fold axis of the rhombohedral cell, as shown in Fig.…”

“…Here, we determine the origin of the magnetically induced ferroelectricity in CaMn 7 O 12 [7] through the analysis of electric polarization, magnetic susceptibility, and neutron powder diffraction measurements. We show that the magnetically induced polarization, the largest measured to date in any compound, develops at 90 K, oriented parallel to the c axis.…”