J. Phys. IV France
Volume 114, April 2004
Page(s) 335 - 337

J. Phys. IV France
114 (2004) 335
DOI: 10.1051/jp4:2004114076

Localization of conduction-band electrons in ${\beta} ''$-(BEDT-TTF) 4 NH 4 [ Cr (C 2O4) 3] ${\cdot} $DMF single crystals

R.B. Morgunov1, 2, 1, A.A. Baskakov1, L.R. Dunin-Barkovskiy1, 2, S.S. Khasanov1, R.P. Shibaeva1, T.G. Prokhorova3, E.B. Yagubskiy3, T. Kato2 and Y. Tanimoto2

1  Institute of Solid State Physics, Chernogolovka 142432, Moscow Region, Russia
2  Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
3  Institute of Problems of Chemical Physics, Chernogolovka 142432, Moscow Region, Russia

Temperature dependence of EPR spectrum of $\beta
$ ?-(BEDT-TTF) 4  NH 4  [ Cr (C 2O 4)3] ${\cdot} $DMF single crystals, which consists of two separate lines characterizing magnetic features of BEDT-TTF and Cr 3+ ions, was studied within the range 1.5-300 K. It was found that reconstruction of the EPR spectrum occurs under decrease of the temperature down to ?  $\approx $ 20 ?. The reconstruction consists in change of Lorentzian shape of the ??DT-TTF line to Gaussian one and in decrease of the effective magnetic moment of ?r 3+ ions. Analysis of temperature and orientation dependencies of parameters of the EPR spectra allows one to suppose that localization of conduction electrons within regions with dimensions close to the size of individual ??DT-TTF molecules occurs at ?  $\approx $ 20 ?. Exchange interactions between ?r 3+ ions change towards antiferromagnetic spin correlations as well. Key words. 2D organic conductors, ${\beta} ''$-(BEDT-TTF) 4  NH 4  [ Cr (C 2O 4)3] ${\cdot} $DMF, ESR, electron localization.

© EDP Sciences 2004