Issue
EPL
Volume 77, Number 3, February 2007
Article Number 37006
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/77/37006
Published online 30 January 2007
EPL, 77 (2007) 37006
DOI: 10.1209/0295-5075/77/37006

A first-principles study of electronic and magnetic properties of a quasi-one-dimensional organic ferromagnet

S. J. Luo1, 2, G. Y. Guo2 and A. Laref2

1  Department of Basic Sciences, Hubei Automotive Industries Institute - Hubei 442002, PRC
2  Department of Physics, National Taiwan University - Taipei 106, Taiwan

shijunluo21c@yahoo.com.cn
gyguo@phys.ntu.edu.tw

received 4 July 2006; accepted in final form 8 December 2006; published February 2007
published online 30 January 2007

Abstract
The magnetic properties of a trans-polyacetylene with either one or two side radicals containing unpaired electrons, have been studied within the density functional theory using the generalized gradient approximation. Results show that a $\pi $-electron spin-polarization cloud appears around the unpaired electrons with alternation of the sign and amplitude of the spin moment extending over the main chain. Furthermore we found that in order to obtain ferromagnetic order in this kind of material, the number of carbon atoms between the two carbon atoms with which the free radicals are connected, should be odd. Additionally, the system has the most stable ferromagnetic state, the strongest ferromagnetism and the highest Curie temperature when the number of the carbon atoms between the two carbon atoms with which the two free radicals are connected, is three. It is shown that dimerization would stabilize the high-spin ground state and hence enforce the ferromagnetism of the quasi-one-dimensional organic ferromagnet. It is also found that dimerization has almost no effect on the electric properties of the quasi-one-dimensional organic metallic-ferromagnet, and therefore, Peierls metal-insulator phase transition would not occur in this system.

PACS
71.15.Mb - Density functional theory, local density approximation, gradient and other corrections.
75.50.Xx - Molecular magnets.
71.20.Rv - Polymers and organic compounds.

© Europhysics Letters Association 2007