Molecule-based Magnet Studied By Green Function Method

Molecule-based magnets are a broad, emerging class of magnetic materials, which have many excellent properties include low density, transparency, electrical insulation, low-temperature fabrication, and so on. Essentially all of the common magnetic phenomena associated with conventional transition-metal and rare-earth-based magnets can be found in molecule-based magnets. Although discovered less than two decades ago, magnets with ordering temperatures exceeding room temperature, very high and very low coercivities, and substantial remanent and saturation magnetizations have been achieved.In this paper, we have applied the multisublattice Green's function technique to study the magnetic properties of a mixed spin-2 and spin-5/2 Heisenberg ferrimagnetic system on a two-dimensional honeycomb lattice. First, we obtained correlation functions of the system using the technique of the equation for Green's functions and the spectral theorem. Then using the correlation function one can get the physical quantities such as the sublattice magnetizations, the critical and compensation temperatures. We calculated numerically these physical quantities for different sets of parameters and give the plots of these physical quantities versus parameters, and investigate the magnetic properties of system.It is shown that the positive energy E+ is sensitive to the change of the next-nearest-neighbor interaction J2 as J1 is fixed, while the negative energy branch E- is insensitive to the change of J2. We found that there are three types of magnetization curves. When only the nearest-neighbor interaction and the single-ion anisotropy interaction are included, there are compensation points at finite temperature. But when the next-nearest-neighbor interaction is included and exceeds a minimum value, the compensation point disappears.It is also shown that the single-ion anisotropies interaction have a great effect on the critical and compensation temperatures.