Carrier transport in the V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) organic-based magnet

The carrier transport of chemical vapor deposition (CVD) prepared films of the room temperature organic-based magnet V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) over a broad temperature and magnetic field range is reported. Due to disorder the [TCNE](·-) sites are located in statistically different environments, and their energies vary from site-to-site, which leads to tailing the density of states into the energy gap, creating electronic traps and suppressing the electron mobility. Conversely, these variations have little effect on the valence band derived from the octahedral V(II)3d(t(2g)) levels, and, hence, on the hole mobility. Presuming a Gaussian distribution of the energies of the localized states in the gap, a model that adequately describes the experimental data is proposed. In this model the T(-1) temperature dependent term was added to the Arrhenius activation energy, Ea, which effectively describes its decrease on cooling. The linear increase of positive magnetoresistance with magnetic field, as well as its weak temperature dependence [ is proportional to (1-T/Tc)(-1/2)] is discussed in terms of a small contribution to Ea associated with the change of magnetic energy.