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

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

Corresponding authors: shijunluo21c@yahoo.com.cn gyguo@phys.ntu.edu.tw

Received: 4 July 2006
Accepted: 8 December 2006

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 -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.