Growth of crystalline C₆₀ by evaporation

This application note describes the growth of crystalline thin films of C6

Van der Waals epitaxy of C₆₀ on the topological insulator Bi₂Se₃

This application note describes the growth of a novel Bi₂Se₃/ C₆₀ heterostructure in the Royce deposition system at the University of Leeds. We also present structural characterisation and transmission electron microscopy data in order to understand nature of the Bi₂Se₃/ C₆₀ interface

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

Observation of a molecular muonium polaron and its application to probing magnetic and electronic states

We thank the Engineering and Physical Sciences Research Council (EPSRC UK) for support via Grants No. EP/M000923/1, No. EP/K036408/1, No. EP/I004483/1, No. EP/S031081/1, and No. EP/S030263/1. L.L., S.S., D.J. and G.T. acknowledge also support from STFC-ISIS Neutron and Muon Source and Ada Lovelace Centre at STFC-SCD. We acknowledge use of the ARCHER (via the U.K. Car–Parrinello Consortium, EP/P022618/1 and EP/P022189/2), U.K. Materials and Molecular Modelling Hub (EP/P020194/1), and STFC Scientific Computing Department's SCARF HCP facilities. We acknowledge support from the Henry Royce Institute. This work was also supported financially through the EPSRC Grant Nos. EP/ P022464/1, and EP/R00661X/1.Muonium is a combination of first- and second-generation matter formed by the electrostatic interaction between an electron and an antimuon (μ+). Although a well-known physical system, their ability to form collective excitations in molecules had not been observed. Here, we give evidence for the detection of a muonium state that propagates in a molecular semiconductor lattice via thermally activated dynamics: a muonium polaron. By measuring the temperature dependence of the depolarization of the muonium state in C60, we observe a thermal narrowing of the hyperfine distribution that we attribute to the dynamics of the muonium between molecular sites. As a result of the time scale for muonium decay, the energies involved, charge and spin selectivity, this quasiparticle is a widely applicable experimental tool. It is an excellent probe of emerging electronic, dynamic, and magnetic states at interfaces and in low dimensional systems, where direct spatial probing is an experimental challenge owing to the buried interface, nanoscale elements providing the functionality localization and small magnitude of the effects.Publisher PDFPeer reviewe

π-anisotropy: A nanocarbon route to hard magnetism

High coercivity magnets are an important resource for renewable energy, electric vehicles, and memory technologies. Most hard magnetic materials incorporate rare earths such as neodymium and samarium, but concerns about the environmental impact and supply stability of these materials are prompting research into alternatives. Here, we present a hybrid bilayer of cobalt and the nanocarbon molecule C60 which exhibits significantly enhanced coercivity with minimal reduction in magnetization. We demonstrate how this anisotropy enhancing effect cannot be described by existing models of molecule-metal magnetic interfaces. We outline a form of anisotropy, arising from asymmetric magnetoelectric coupling in the metal-molecule interface. Because this phenomenon arises from π−d hybrid orbitals, we propose calling this effect π-anisotropy. While the critical temperature of this effect is currently limited by the rotational degree of freedom of the chosen molecule, C60, we describe how surface functionalization would allow for the design of room-temperature, carbon-based hard magnetic films

Tuning the magnetic properties of Fe thin films with RF-sputtered amorphous carbon

RF-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. This paper describes changes in the magnetic properties of iron thin films with a-C overlayers. In as-deposited samples, hybridisation and intermixing at the Fe/a-C interface leads to magnetic softening (Liu et al., 2006) [1], with a reduction in the coercive field (Hc) up to a factor of five for Fe/a-C/Fe trilayers, and a 10–30% lower saturation magnetization as a function of the metal film thickness. After annealing at 500 °C, inter-diffusion and graphitization of the carbon layer results in up to a factor five increased coercivity due to increased pinning as shown via Kerr microscopy. Therefore, RF-sputtered carbon overlayers and post-processing can tune the anisotropy and domain configuration of metallic thin films in a synthesis methodology that is simple, cheap and sustainable

Reversible spin storage in metal oxide—fullerene heterojunctions

We show that hybrid MnOx/C60 heterojunctions can be used to design a storage device for spin-polarized charge: a spin capacitor. Hybridization at the carbon-metal oxide interface leads to spin-polarized charge trapping after an applied voltage or photocurrent. Strong electronic structure changes, including a 1-eV energy shift and spin polarization in the C60 lowest unoccupied molecular orbital, are then revealed by x-ray absorption spectroscopy, in agreement with density functional theory simulations. Muon spin spectroscopy measurements give further independent evidence of local spin ordering and magnetic moments optically/electronically stored at the heterojunctions. These spin-polarized states dissipate when shorting the electrodes. The spin storage decay time is controlled by magnetic ordering at the interface, leading to coherence times of seconds to hours even at room temperature