Doping of Multiferroic Bulk and Nanosized Objects. Theoretical Model (part i)

Doping provides the opportunity to manipulate extensively the multiferroic properties of compounds and substances with the aim of achieving "room-temperature multiferroism". A theoretical foundation for substitutional doping has been constructed based on defined microscopic Hamiltonians describing the magnetic and ferroelectric subsystems and their interactions. Through a comprehensive analysis of the potential consequences of doping compounds with magnetic and non-magnetic ions of arbitrary valency, theoretical investigations have been conducted on changes in interactions within the magnetic and polarization systems and between them. Using the Green's function method, analytical expressions for polarization and magnetization, energies of spin, pseudo-spin, electronic, and lattice excitations, bandgap width, and dielectric function beyond the framework of the random phase approximation have been derived. Based on this model (in Part II of this development), approaches to doping can be elucidated, allowing the observation of multiferroic properties at room temperature.