Theoretical approach for computing magnetic anisotropy in single molecule magnets

Raghunathan, Rajamani and Ramasesha, Suryanarayanasastry and Diptiman, Sen (2008) Theoretical approach for computing magnetic anisotropy in single molecule magnets. In: PHYSICAL REVIEW B, 78 (10). 104408-1-104408-8.

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Abstract

We present a theoretical approach to calculate the molecular magnetic anisotropy parameters, $D_{M}$ and $E_M$ for single molecule magnets in any eigenstate of the exchange Hamiltonian, treating the anisotropy Hamiltonian as a perturbation. Neglecting intersite dipolar interactions, we calculate molecular magnetic anisotropy in a given total spin state from the known single-ion anisotropies of the transition metal centers. The method is applied to $Mn_{12}Ac$ and $Fe_8$ in their ground and first few excited eigenstates, as an illustration. We have also studied the effect of orientation of local anisotropies on the molecular anisotropy in various eigenstates of the exchange Hamiltonian. We find that, in case of $Mn_{12}Ac$, the molecular anisotropy depends strongly on the orientation of the local anisotropies and the spin of the state. The $D_M$ value of $Mn_{12}Ac$ is almost independent of the orientation of the local anisotropy of the core Mn(IV) ions. In the case of $Fe_8$, the dependence of molecular anisotropy on the spin of the state in question is weaker. We have also calculated the anisotropy constants for several sets of exchange parameters and found that in $Mn_{12}Ac$ the anisotropy increases with spin excitation gap, while in $Fe_{8}$, the anisotropy is almost independent of the gap.

Item Type:	Journal Article
Publication:	PHYSICAL REVIEW B
Publisher:	The American Physical Society
Additional Information:	Copyright of this article belongs to The American Physical Society.
Keywords:	TRANSITION-METAL-COMPLEXES; FREQUENCY EPR-SPECTRA; ELECTRONIC-STRUCTURE; OPTICAL-PROPERTIES; AB-INITIO; FIELD; BARRIER; CRYSTAL; CLUSTER; ION
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit Division of Physical & Mathematical Sciences > Centre for High Energy Physics
Date Deposited:	28 Jan 2010 06:55
Last Modified:	19 Sep 2010 04:52
URI:	http://eprints.iisc.ac.in/id/eprint/16456

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