Anomalous Non-Linear to Linear Shift in Magnetoresistance of Amorphous Carbon Films

Abstract

Non-linear to linear negative magnetoresistance (MR) was studied under the magnetic field ranging from −7 T to 7 T with a change in measurement temperature from 2 K to 300 K. Under the magnetic field of 7 T, a maximum MR magnitude of 8.2% was observed at 2 K. The chemical vapor deposition technique was adopted to synthesize the amorphous carbon thin films. Non-saturated and non-linear negative MR was observed for the lower temperatures, while 10 K was observed as transition temperature. Afterwards, the more likely linear MR behavior was observed up to 300 K. MR shape change was correlated with the structural morphology of metallic disordered graphitic layers or the random stacking of graphene layers with amorphous carbon. The negative MR mechanism for such a non-linear to linear shift was partially assumed as a combined effect of the diffused scattering theory and the weak localization theory. The negative MR effect has a direct relation with the degree of structural order.

Substrate Impact on MR Characteristics of Carbon Nano Films Explored via AFM and Raman Analysis

“…As the carbon material consisted of a majority of sp 2 clusters and are good conductors, while the carbon material consisted of a majority of sp 3 clusters and are not good conductors [26], the samples with a larger C(sp 2 )/C(sp 3 ) ratio will have excellent conduction properties. We observed the magnitude for the sp 2 cluster ratio of 85% for the a-Carbon on the SiO 2 specimen, as shown in Figure 5b.…”

“…Subsequently, we have recently performed a series of experiments, in which we have reported on a-Carbon structure-dependent MR properties, and we reported an enhanced angular MR of 18% and negative MR of 13% for a-Carbon thin films fabricated through a CVD technique. Furthermore the mechanism of such MR properties was investigated and it was found that they greatly depend on grain boundary scattering (GBS) and weak localization theory (WLT) [25,26]. Furthermore, the correlation of MR of a-Carbon with spintronics, has greatly demanded attention in recent years owing to its magnetoresistance applications; for higher magnetic fields, a-Carbon MR is still considered as unsaturated.…”