Emergent Spin Ordering at C60 interfaces

This work is a pioneer study on the role played by molecular interfaces in altering the electronic states of non-ferromagnetic materials. Here, we consider diamagnetic copper and paramagnetic manganese and scandium, to overcome the Stoner criterion and make them magnetically ordered at room temperature. The mechanism is mediated by the charge transfer from the transition metal and hybridization with molecular carbon, creating new 3d-π that drastically modify the electron energy bands around the Fermi energy of both metal and molecule. This effect is achieved via interfaces between metallic thin films and C60 molecular layers. The emergent spin ordering arising in these systems is measured using magnetometry shows magnetically ordered behaviour at room temperature, but dependent on the thickness and continuity of the metallic layer. To determine how in the layered structure the emergent spin ordering is distributed, low-energy muon spin spectroscopy is utilised by studying the depolarization process of low-energy muons implanted in the sample. This technique indicates localised spin-ordered states at, and close to, the metallo-molecular interface. X-ray absorption spectroscopy provides an excellent tool for identifying the emergent spin ordering of specific elements within a sample. The change in the molecular orbitals of C60 due to charge transfer and 3d-π hybridization is evaluated based on this technique. The presence of spin ordering in a non-magnetic metallic host due to molecular charge transfer has a drastic effect not only on the magnetic but also on the transport properties of the system. The decisive role of the molecular interfaces in the physics of spin dependent scattering within a non-magnetic host has been demonstrated. Localised spin ordering leads to changes in the Kondo and weak localisation effects with applications in low temperature thermometry and quantum devices. It is found that there is an additional magnetic scattering that has a pronounced contribution when C60 molecules are embedded into the non-magnetic Cu and hence creates localised spins. The localised spin ordering that emerged at molecular interfaces is a new approach for novel generation of materials for future spintronics devices

Optical conversion of pure spin currents in hybrid molecular devices

Carbon-based molecules offer unparalleled potential for THz and optical devices controlled by pure spin currents: a low-dissipation flow of electronic spins with no net charge displacement. However, the research so far has been focused on the electrical conversion of the spin imbalance, where molecular materials are used to mimic their crystalline counterparts. Here, we use spin currents to access the molecular dynamics and optical properties of a fullerene layer. The spin mixing conductance across Py/C60 interfaces is increased by 10% (5 × 1018 m−2) under optical irradiation. Measurements show up to a 30% higher light absorbance and a factor of 2 larger photoemission during spin pumping. We also observe a 0.15 THz slowdown and a narrowing of the vibrational peaks. The effects are attributed to changes in the non-radiative damping and energy transfer. This opens new research paths in hybrid magneto-molecular optoelectronics, and the optical detection of spin physics in these materials

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

Dataset associated with 'Discrete Hall resistivity contribution from Néel skyrmions in multilayer nanodiscs'

Magnetic skyrmions have excited much interest as the basis for novel data storage applications in which information is encoded and transferred in these magnetic knot-like quasiparticles. The proposed read-out of any such skyrmion-based spintronic device will rely upon the electrical detection of a single magnetic skyrmion within a nanostructure, through, for example, a change in the Hall resistivity. We have fabricated nanodiscs from multilayers of Pt/Co/Ir which can support skyrmions at room temperature and have measured the Hall resistivity whilst simultaneously imaging the spin texture using magnetic scanning transmission x-ray microscopy. We show that the Hall resistivity is correlated to both the presence and size of a magnetic skyrmion in the nanodisc and that the size-dependent part matches the expected anomalous Hall signal when averaging the magnetisation over the disc. The additional contribution arising from the presence of the single skyrmion is 11±1 nΩ cm

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)