Electron transfer and spin injection in C60-ferromagnetic composites

• Main Author: Moorsom, Timothy
• Other Authors: Cespedes, Oscar
• Published: University of Leeds 2016
• Subjects: 620.1
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.698249

The magnetic properties of spin doped fullerenes are investigated in hybrid organic/inorganic structures with the aim of establishing the extent to which magnetic states can be induced and controlled in these materials. Volume magnetometry is used to measure a reduction of net magnetization and an increase in coercivity in cobalt which can be understood in terms of a transfer of majority spin electrons from the transition metal d-band into spin polarized hybrid interface states. This is supported by PNR and XAS studies of Co/C60 which reveal AF coupling between Co metal films and a hybrid interfacial region where magnetic ground states are induced in fullerenes through charge transfer. Investigations of hybridization between C60 and the RE-TM alloy CoGd show that the compensation temperature of the ferrimagnet is altered by the presence of C60. PNR measurements of CoGd/C60 MLs reveal interfacial coupling which creates an AF region 1.5 $\pm$ 0.1 nm thick. Magnetometry of Gd/C60 bilayers indicates that hybridization between the metal conduction bands and the C60 LUMO modifies magnetic ordering in Gd. This is supported by the observation of novel features in the temperature dependence of magnetization and resistivity in the composite. XAS of Gd/C60 bilayers shows a large peak in the carbon K-edge at 282 eV which is attributed to interfacial hybridization. It is shown that PL quenching in C60 is greater over Co than Au which is attributed to the greater electron transfer between Co and C60. PL quenching is proposed as an effective way to measure magnetic coupling and electron transfer in interfaces. Raman spectra are recorded in C60 junctions during spin polarised transport. The Ag(2) peak splitting is shown to depend on the polarisation of injected current acting as an effective probe of triplet formation in C60. Finally, XAS at the carbon K-edge is recorded during spin transport. A suppression of the LUMO to zero and increase in the intensity of the 282 eV peak occurs after removal of external bias and is shown to be reversible and repeatable under cycles of grounding and charge injection. A proposed mechanism involving the redistribution of charge following the removal of bias which causes electrons to become trapped in interfacial states is suggested.