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Magnetic Exchange Calculations for Porphyrin based Structures

Sankar Kesanakurthi ,  Nadjib Baadji ,  Stefano Sanvito 

Trinity College, Deptartment of Physics, College Green, Dublin Dublin 2, Ireland
Trinity College Dublin, CRANN, Chemistry and Physics Departments, Dublin Dublin 2, Ireland

Abstract
Current interest in transition metal-based molecular magnets like Fe-Porphyrin stems from the tantalizing prospect of future molecular-based magnetic storage devices. Porphyrins, which have been for long time at the center of a large research activity in biology, are now taking an important place in spintronics. In general, organic materials are interesting since the weak spin-orbit coupling and very long spin-relaxation times make them ideal media to propagate spin information. In addition to this, magnetic-Porphyrins carry intrinsic magnetic moment that can be exploited for constructing all-organic spin-devices. Finally and equally important Porphirins can be arranged in large molecular-superstructures with magnetic properties that can be largely tailored. In this contribution we investigate theoretically the magnetic ground state of various Fe-porphirins complexes by using ab-initio density functional theory as numerically implemented in the SIESTA code [1].

In particular we will present results for three different structures all derived from Fe-porphyrins, namely Fe-porphyrin dimers, Fe-porphyrin deposited on Ni substrates and Fe-porphyrin double decker with TCNE bridges. In all the three cases we perform a detailed analysis of the local density of state with the aim of identifying the mechanism for the magnetic coupling or for the absence of it. Finally we will discuss the difficulties in obtaining the desired exchange coupling in some structures and the possible solutions to overcome these hurdles.

References
[1] J.M. Soler, E. Artacho, J.D. Gale, A. Garcia, J. Junquera, P. Ordejon and D. Sanchez-Portal, J. Phys.: Condens. Matter 14 2745 (2002)

 

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium E, by Sankar Kesanakurthi
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-04 17:16
Revised:   2009-06-07 00:48