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Constructing Asymmetrical Ni-centered {NiN2O4} Octahedra in Layered Metal-organic Structures for Near-room-temperature Single-phase Magnetoelectricity
K. Mao, J. Zhang, Z. Guo, L. Liu*, H. Ma, Y. Y. Chin, H. J. Lin, S. Bao*, H. Xie, R. Yang, Z. Jing, J. Shen, G. Yuan, J. Chen, P. Wu, and X. Wu*
Layered metal–organic structures (LMOSs) as magnetoelectric (ME) multiferroics have been of great importance for realizing new functional devices in nanoelectronics. Until now, however, achieving such room-temperature and single-phase ME multiferroics in LMOSs have proven challenging due to low transition temperature, poor spontaneous polarization, and weak ME coupling effect. Here, we demonstrate the construction of a LMOS in which four Ni-centered {NiN2O4} octahedra form in layer with asymmetric distortions using the coordination bonds between diphenylalanine molecules and transition metal Ni(II). Near room-temperature (283 K) ferroelectricity and ferromagnetism are observed to be both spontaneous and hysteretic. Particularly, the multiferroic LMOS exhibits strong magnetic-field-dependent ME polarization with low-magnetic-field control. The change in ME polarization with increasing applied magnetic field μ0H from 0 to 2 T decreases linearly from 0.041 to 0.011 μC/cm2 at the strongest ME coupling temperature of 251 K. The magnetic domains can be manipulated directly by applied electric field at 283 K. The asymmetrical distortion of Ni-centered octahedron in layer spurs electric polarization and ME effect and reduces spin frustration in the octahedral geometry due to spin-charge-orbital coupling. Our results represent an important step toward the production of room-temperature single-phase organic ME multiferroics.