This research consideres the effect of molecular overlayers on the spin Hall magnetoresistance (SHMR) and anisotropic magnetoresistance (AMR) of heavy metals (Pt, Ta, and PtMn). The objective is to investigate the effect of molecular overlayers on the effective spin orbit coupling (SOC), i.e. the charge-spin conversion of heavy metals. We have pursued this objective by measuring the SHMR & the AMR in YIG/Metal and YIG/Metal/C60 structures. This effect has generated a large interest over the last few years, and they are critical in the study of the spin Hall angle and its applications, e.g. for devices such as spin torque MRAM.
"In this study" when C60 is grown on a metal, the electronic structure is altered due to hybridisation and charge transfer. A conducting layer with high SOC is formed at the interface between a heavy metal and molecules. The SHMR for Pt/C60 and Ta/C60 at room temperature are up to a factor 6 higher than for the pristine metals, with the spin Hall angle increased by 20-60 %. At low fields of 1-30 mT, there is an AMR which increases up to 700 % at room temperature by C60. Given the dielectric properties of C60, this opens the possibility of gating the effective SOC of metals, with applications for spin transfer torque memories and pure spin current dynamic circuits.
Annealing sample plays a crucial part in our transport properties of (Pt, PtMn) and (Pt, PtMn)/C60 because of changes to the crystallinity and metallo-molecular coupling at the interface. As a result, the SHMR/MR can increase by a further factor 4 when annealing at a temperature of 300 ◦C.
