First-Principles Study Of Magnetism In Organic Molecules DDQ-TM2 And Determination Of The In-plane Anisotropy Field In Hexagonal Systems Via Rotational Magnetization: Theoretical Model And Monte Carlo Simulations

As the requirement of magnetic materials, organic magnetic materials which have low density and high plasticity have received much attention. But in the experiment most of these materials show small molecular magnet and low Curie temperature. In order to synthesize the organic magnets which have an above room temperature Curie temperature, magnetic theory of the origin and mechanism of the exchange became extremely important.In this paper, first principles was did based on the calculation software vasp. According to the molecular structure and chemical properties, we built a possible structure which only contain a single-molecule organic magnets DDQ-TM2. Using the structural model, we calculated the ground state, charge density, spin density, density of materiald, and the magnetic properties of the molecules was analyzed based on the caculation.In the calculation of the TM2·O·DDQ system we found that ferromagnetic property of is caused by the super-exchange interaction. Because of the competition between super-exchange and direct exchange, the whole 3d systems show a series of different magnetic properties. Magnetic moment of Ni2-ddq system mostly origins from the Ni ions and polarization of particles or clusters around the Ni ions. We also calculated the system contains different 3d metal atoms which totally have 10 valence d-electrons. We got a we a similar density of state to the one in letters, and it confirmed that in this system the semi-metallic anti-ferromagnetic is possible.In this paper, we also did some calculation work at theory of experience. We developed an new method to measure the high order anisotropy constant of materials. In the method,we deduced the magnetic anisotropy field of thin films which have in-plane uni axial anisotropy, from the measured rotation magnetization curve (RMC),which can be measured in a rotating magnetic field while the size of the field are fixed. We did a precise theoretical derivation of the method based on calculating the minima of total energy. We explained the reason of the difference between the theoretical curve and experiment curve in the case of h<0.5, concluding that it is caused by coercive force's effect to the magnetization reversal of magnetic moment. In this paper we used the method to investigate the hexagonal crystal system samples which have the in-plane uniaxial anisotropy. We analyze the rotation magnetization curve (RMC) of hexagonal crystal system under a series of different field. The theoretical calculations are consistent with Monte Carlo simulation results. Research shows that the magnetization rotation provides a new way to measure high-order hexagonal magnetic anisotropy constant K3.