Emergent magnetism at transition-metal–nanocarbon interfaces

Charge transfer at metallo–molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc–C60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo–carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp3 orbitals are annealed into sp2−π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz–π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices

TUNEABLE MAGNETIC PROPERTIES OF 3D TRANSITION METALS USING CARBON ALLOTROPES

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. Kerr microscopy 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

Photocatalytic Performance Improvement by Doping Ag on ZnO/MWCNTs Nanocomposite Prepared with Pulsed Laser Ablation Method Based Photocatalysts Degrading Rhodamine B Organic Pollutant Dye

ZnO/MWCNTs nanocomposite has significant potential in photocatalytic and environmental treatment. Unfortunately, its photocatalytic efficacy is not high enough due to its poor light absorbance and quick recombination of photo-generated carriers, which might be improved by incorporation with noble metal nanoparticles. Herein, Ag-doped ZnO/MWCNTs nanocomposite was prepared using a pulsed laser ablation approach in the liquid media and examined as a degradable catalyst for Rhodamine B. (RhB). Different techniques were used to confirm the formation of the nanostructured materials (ZnO and Ag) and the complete interaction between them and MWCNTs. X-ray diffraction pattern revealed the hexagonal wurtzite crystal structure of ZnO and Ag. Additionally, UV-visible absorption spectrum was used to study the change throughout the shift in the transition energies, which affected the photocatalytic degradation. Furthermore, the morphological investigation by a scanning electron microscope showed the successful embedding and decoration of ZnO and Ag on the outer surface of CNTs. Moreover, the oxidation state of the formed final nanocomposite was investigated via an X-ray photoelectron spectrometer. After that, the photocatalytic degradations of RhB were tested using the prepared catalysts. The results showed that utilizing Ag significantly impacted the photo degradation of RhB by lowering the charge carrier recombination, leading to 95% photocatalytic degradation after 12 min. The enhanced photocatalytic performance of the produced nanocomposite was attributed to the role of the Ag dopant in generating more active oxygen species. Moreover, the impacts of the catalyst amount, pH level, and contact time were discussed

Photodetection Properties of CdS/Si Heterojunction Prepared by Pulsed Laser Ablation in DMSO Solution for Optoelectronic Application

The high-quality n-type CdS on a p-type Si (111) photodetector device was prepared for the first time by a one-pot method based on an ns laser ablation method in a liquid medium. Cadmium target was ablated in DMSO solution, containing sulfur precursor, and stirred, assisting in 1D-growth, to create the sulfide structure as CdS nano-ropes form, followed by depositing on the Si-substrate by spin coating. The morphological, structural, and optical characteristics of the CdS structure were examined using X-ray diffraction, transmission, and scanning electron microscopy, photoluminescence, and UV-VIS spectroscopy. From X-ray diffraction analysis, the growing CdS spheres have a good crystal nature, with a high purity and desired c-axis orientation along the (002) plane, and the crystallinity was around 30 nm. According to optical characterization, high transparency was found in the visible–near-infrared areas of the electromagnetic spectrum, and the CdS spheres have a direct optical energy band gap of 3.2 eV. After that, the CdS/Si hetero-structured device was found to be improved remarkably after adding CdS. It showed that the forward current is constantly linear, while the dark current is around 4.5 µA. Up to a bias voltage of 4 V, there was no breakdown, and the reverse current of the heterojunctions somewhat increased with reverse bias voltage, while the photocurrent reached up to 580 and 690 µA for using 15 and 30 W/cm2 light power, respectively. Additionally, the ideal factors for CdS/Si heterojunction were 3.1 and 3.3 for 15 and 30 W/cm2 light power, respectively. These results exhibited high performance compared to the same heterojunction produced by other techniques. In addition, this opens the route for obtaining more enhancements of these values based on the changing use of sulfide structures in the heterojunction formation

Data on Emergent Magnetism in Metallo-Carbon Interfaces.

Data as presented in the paper by Fatma Al Ma'Mari et al. In the journal Proceedings of the National Academy of Sciences of the United States of America vol. 114 (22), pp 5583-5588 (2017)