The structural and organic magnetoresistance response of poly(9-vinyl carbazole) using low applied magnetic fields and magnetic nanoparticle addition

Abstract

Herein, we report the tuning of the structural and organic magnetoresistance response of poly(9-vinyl carbazole) (PVK) with magnetic nanoparticle addition under exposure to low applied magnetic fields. X-ray diffraction analysis showed evidence of PVK conformational changes by either adding magnetic nanoparticles or by applying an external magnetic field. Molecular dynamics simulations suggested that the loss of aromaticity could lead to slight but detectable modifications in the PVK structure. Confocal Raman spectroscopy under low applied magnetic field evidenced modifications in PVK singlet and triplet populations followed by theoretical simulation to assign the vibrational modes in PVK different multiplicities. Both the addition of magnetic nanoparticles and the presence of an applied magnetic field showed an increase in the PVK triplet-to-singlet ratio. PVK nanocomposites showed negative low field magnetoresistance (MR) reaching maximum values of MR (2 kOe) = −1.1 and −9.0% for T = 280 and 20 K, respectively. The MR dependence with low applied magnetic fields showed a typical behavior in agreement with the electron–hole recombination mechanism. This latter effect could be experimentally associated with the change in the PVK triplet-to-singlet ratio, as observed by Raman analysis. In addition, the PVK magnetoresistance effect could also be ascribed to conformational changes induced by the presence of magnetic nanoparticles and an applied magnetic field, as evidenced by X-ray diffraction analysis.