Theoretical investigation of multiferroic metal–organic framework magnet [CH3NH3][Co(HCOO)3]: Green’s function method

: For the first presented magnetic ordering-induced multiferroics with a metal-organic framework (MOF) of formula [CH3NH3][Co(HCOO)3], we theoretically investigate its multiple ferroics. It is found that Dzyaloshinskii-Moriya interaction is a main cause that leads to non-zero magnetization, and electric polarization, and the induced electric polarization can be regulated by magnetic fields. As an assistant mechanism, magnon-magnon interaction and quantum fluctuation play an important role on ferroelectrics and magnetism. Our methods are based on the double-time Green's function and Holstein-Primakoff transformation. Theoretical results can be compared with experiments, though there are some discrepancies.