Magnetoelectric multiferroics have received much attention in the past decade due to their interesting physics and promising multifunctional performance. For practical applications, simultaneous large ferroelectric polarization and strong magnetoelectric coupling are preferred. However, these two properties have not been found to be compatible in the single-phase multiferroic materials discovered as yet. Here, it is shown that superior multiferroic properties exist in the A-site ordered perovskite BiMn Cr O synthesized under high-pressure and high-temperature conditions. The compound experiences a ferroelectric phase transition ascribed to the 6s lone-pair effects of Bi at around 135 K, and a long-range antiferromagnetic order related to the Cr spins around 125 K, leading to the presence of a type-I multiferroic phase with huge electric polarization. On further cooling to 48 K, a type-II multiferroic phase induced by the special spin structure composed of both Mn- and Cr-sublattices emerges, accompanied by considerable magnetoelectric coupling. BiMn Cr O thus provides a rare example of joint multiferroicity, where two different types of multiferroic phases develop subsequently so that both large polarization and significant magnetoelectric effect are achieved in a single-phase multiferroic material.

The magnetoelectric multiferroicity is not expected to occur in a cubic perovskite system due to the high structural symmetry. By versatile measurements in magnetization, dielectric constant, electric polarization, neutron and X-ray diffraction, Raman scattering as well as theoretical calculations, we reveal that the A-site ordered perovskite LaMn 3 Cr 4 O 12 with cubic symmetry is a novel spin-driven multiferroic system with strong magnetoelectric coupling effects. When magnetic field is applied in parallel/perpendicular to electric field, the ferroelectric polarization can be enhanced/suppressed significantly. The unique multiferroic phenomenon observed in this cubic perovskite cannot be understood by conventional spin-driven microscopic mechanisms. Instead, a nontrivial effect involving the interactions between two magnetic sublattices is likely to play a crucial role. 3The magnetoelectric (ME) multiferroicity with coupled ferroelectric and magnetic orders have received much attention due to their great potential for numerous applications [1][2][3][4][5][6][7][8]. Perovskite is one of the most important material systems for multiferroic study. Since the discovery of multiferroic behaviors in perovskite BiFeO 3 and TbMnO 3 [2,3], a large number of multiferroic materials with different physical mechanisms have been found in the last decade [9][10][11][12][13]. Among them, the spin-induced multiferroics have received the most attention because the ferroelectricity is induced by magnetic structures so that a strong ME coupling would be expected [14][15][16]. Several theories such as spin-current model (or inverse Dzyaloshinskii-Moriya interaction), exchange striction mechanism and d-p hybridization mechanism have been proposed to account for the spin-induced ferroelectricity in ME multiferroics by special spin textures such as non-collinear spiral spin structures and collinear E-type antiferromagnetic (AFM) structure with zigzag spin chains [17][18][19][20][21]. It is well known that a cubic perovskite lattice is unfavorable for ferroelectricity due to the existence of an inversion center. However, the total symmetry for an ME multiferroics is the product of the crystal and magnetic symmetries. Therefore, in principle, it is possible to find an ME multiferroics in a cubic perovskite system if its magnetic structure breaks the space inversion symmetry. Nevertheless, such an intriguing case has never been found in previous studies. 4The A-site ordered perovskite with a chemical formula of AA′ 3 B 4 O 12 provides an opportunity for searching ME multiferroics in a cubic lattice.This type of ordered perovskite can be formed when three quarters of the A-site of a simple ABO 3 perovskite is substituted by a transition-metal ion A′ (Fig. 1a) [22]. Since both A′ and B sites accommodate magnetic transition-metal ions, multiple magnetic interactions may develop while the crystal structure can be finely tuned by selecting appropriate A′ and B elements to maintain a cubic lattice [23][24][25][26][27]. In this lette...