Identifier: imarina:6179165
Authors:
De Graaf, Cornelis
Abstract:
© Springer-Verlag Berlin Heidelberg 2017. Zero-field splitting (ZFS) is one of the essential ingredients for the occurrence of magnetic bistability at a molecular level. It is commonly understood as the loss of degeneracy of the spin components of a spin-orbit free electronic state in the absence of an external magnetic field. The loss of degeneracy finds its origin in the combined action of spin-orbit coupling and an anisotropic crystal field exerted on the magnetic center. Although ZFS was already described in the early days of quantum mechanics, it became a central issue of many theoretical and experimental studies after the discovery of single-molecule magnet behavior about twenty years ago. Moreover, ZFS also plays an important role in the magnetic properties of multiferroic solid state compounds, where electric and magnetic properties are intrinsically coupled and one may induce magnetic phase transitions by applying an external electric field, or vice versa. ZFS is commonly described in terms of model Hamiltonians that are basically introduced on a phenomenological basis. Typically, these model Hamiltonians only contain spin operators, since the ZFS applies by definition only to systems where the ground state orbital configuration is well separated from the other configurations (i.e., no orbital degree of freedom), and hence, the effective description of the low-lying energy levels can be restricted to the spin variables. This chapter aims to fill the gap between ab initio calculations based on the full electronic Hamiltonian and the phenomenological Hamiltonians used to describe ZFS. In this way, the model Hamiltonians can be validated and put on a rigorous foundation. Moreover, we establish magneto-structural correlations and demonstrate that these correlations
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