Layered perovskites A 3 M 2 O 7 are known to exhibit the so-called hybrid improper ferroelectricity. Despite experimentally confirmed cases (e.g. nonmagnetic M =Ti and Sn), the ferroelectricity in magnetic Ca 3 Mn 2 O 7 remains a puzzle. Here, the structural, ferroelectric, magnetoelectric, and optical properties of Ca 3 Mn 2 O 7 are systematically investigated. Switchable polarization is directly measured, demonstrating its ferroelectricity. In addition, magnetoelectric response is also evidenced, implying the coupling between magnetism and ferroelectricity. Furthermore, strong visible light absorption is observed, which can be understood from its electronic structure. Its direct and appropriate band gap, as well as wide conducting bands, makes Ca 3 Mn 2 O 7 a potential candidate for ferroelectric photoelectric applications.

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The ferroelectric and tunnel electro- and magnetoresistance properties in La0.6Sr0.4MnO3/BiFeO3/La0.6Sr0.4MnO3 multiferroic tunnel junctions sandwiched with the antiferromagnetic-ferroelectric BiFeO3 as a tunnel barrier were reported. Besides the four non-volatile resistance states and the interfacial magnetoelectric coupling effect with the tunnel magnetoresistance manipulated by ferroelectric polarizations, one of the most important results is that the exchange bias effect on the tunnel magnetoresistance is observed in this junction due to the magnetic interaction between antiferromagnetic BiFeO3 and ferromagnetic La0.6Sr0.4MnO3 layers. These finds may be helpful for designing exchange bias based multiferroic tunnel junction in next generation random access memory devices.