Tuneable Magnetic Properties of 3D Transition Metals Using Carbon Allotropes
|Dr. Oscar Cespedes
|SHOUG MOHAMMAD ALI ALGHAMDI
|PHYSICS - SOLID EXPERIMENTAL
|UNIVERSITY OF LEEDS
|This research describes changes in the magnetic properties of 3d transition metals with hybrid nanocarbon and molecular carbon interfaces. Sputtered amorphous carbon (a-C) offers a simple and cheap pathway to tune the magnetic properties of transition metal thin ﬁlms for magnetic memories and different spintronic applications. Here, amorphous nanocarbon ﬁlms were RF-sputtered. Annealing the ﬁlms changed the structure from amorphous to nanocrystalline as determined by Raman spectroscopy. The RF-sputtered a-C ﬁlms were then coupled with pure iron (Fe) and iron nitride (FexN(1−x)) to study the magnetic properties for both hybrid interfaces at different annealing temperatures. Before annealing, hybridisation at the Fe/a-C interface leads to magnetic softening, with a reduction in coercivity (Hc) up to a factor of 5 for a Fe/a-C/Fe trilayer and a 10-30% lower saturation magnetisation as a function of the metal ﬁlm thickness. On the other hand, after annealing, inter-diffusion and graphitisation of the carbon layer results in increased coercivity, also by a factor of 5, with the highest energy product being of the order of 53 kJ per m3 of iron in a 10 nm ﬁlm annealed at 500◦C. Kerrmicroscopy images of the ﬁlms show a reduction in domain size and increased pinning points after annealing. Similar results were obtained when Fe is doped with nitrogen, with a BH(max) of 9 kJ per m3 in a 9 nm FexN(1−x)/with RF-sputtered a-C was annealed at 500 ◦C. RF-sputtered carbon overlayers and post-processing can therefore be used to tune the anisotropy, domain conﬁguration and magnetic properties of metallic thin ﬁlms in a synthesis methodology that, for some applications in thin ﬁlm technologies, could be simpler and cheaper than the use of heavy noble metals and/or rare earths. C60 was also coupled with Fe and Co and the resulting Fe/C60 bilayer samples show changes in Hc after annealing when the metallic layer is > 4 nm. Low temperature experiments at Co/C60 exhibited massive increases in coercivity (Hc). The Hc also rose as a result of annealing the ﬁlm. Low temperature MR measurements point to an exchange spring effect. The research ﬁndings emphasise the importance of the hybridisation effects between the nanocarbon and molecular π orbitals and 3d bands of metals in controlling the magnetic properties at the interfaces before and after annealing.
|Tuneable Magnetic Properties of 3D Transition Metals Using Carbon Allotropes
|SACM - United Kingdom