Magnetic properties of ZnFe2O4: First-principles calculations

• Main Authors: Ching-Sheng Liu, 劉晉生
• Other Authors: Ching Cheng
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/36046595630156315526

碩士 === 國立成功大學 === 物理學系碩博士班 === 95 === In this thesis, structures of different configurations in magnetic ordering for ZnFe2O4 were constructed to investigate the magnetic and structural properties of this material. The calculated lowest energy structure was found to be different from the conventionally regarded magnetic structure of ZnFe2O4. The Heisenberg model with up to the 4th neighbour interactions was employed to describe the total energies of the seven structures with different magnetic ordering to obtain the interaction energies between the magnetic dipole moments of Fe atoms in the material. In case only up to the 2nd nearest-neighbour interactions was included, the nearest-neighbour (nn) and next nearest-neighbour (nnn) interactions were found to be antiferromagnetic and ferromagnetic respectively with the magnitude of the nn interaction about thrice of that of the nnn interaction. However, much lower consistent results were obtained when the 4th neighbour interactions were included in describing the total energies for these seven structures of different magnetic ordering for ZnFe2O4. Similar conclusions were reached when different constraints were applied in the relaxation processes, i.e. relaxation with constrained cubic geometry, relaxation with allowed shape change for unit cell and relaxation with ionic relaxation applied to O atoms only. The inconsistency in applying the Heisenberg model of up to the 4th neighbour interactions indicates the complexity of magnetic ordering in this material and models beyond the present consideration, e.g. including noncolinearity and different interacting paths, need to be included in the future studies.