Tatiana Makarova

Magnetism in photopolymerized fullerenes

Abstract The phototransformation of bulk C60 and laser- and electron-beam treatment of C60 films in air changes their magnetic properties. Nonlinear magnetization is observed only for samples irradiated in the presence of oxygen, while, in the case of pressure-polymerized C60, oxygen adversely affects the magnetic properties. The contrasting roles of oxygen in these processes are discussed. Magnetic force microscopy shows that laser- and electron-beam irradiation of fullerene films produces magnetic images which are highly correlated with the topographic images.

Observation of intrinsic magnetic domains in C60 polymer

A C60 polymer has been characterized for the first time with respect to impurity content and ferromagnetic properties by laterally resolved particle induced X-ray emission (PIXE), superconducting quantum interference device (SQUID) and magnetic force microscopy (MFM) in order to detect intrinsic ferromagnetic domains. In parts of the pure regions (concentration of magnetic impurities <1 μg/g), we found stripe-domain magnetic images with different orientations of domain magnetization. The size of the regions where magnetic domains were observed is ∼30% of the pure region. All these results reveal that the polymerized C60 sample is a mixture of magnetic and non-magnetic parts and only a fraction of the sample contributes to the ferromagnetism.

Edge state magnetism in zigzag-interfaced graphene via spin susceptibility measurements

Development of graphene spintronic devices relies on transforming it into a material with a spin order. Attempts to make graphene magnetic by introducing zigzag edge states have failed due to energetically unstable structure of torn zigzag edges. Here, we report on the formation of nanoridges, i.e., stable crystallographically oriented fluorine monoatomic chains, and provide experimental evidence for strongly coupled magnetic states at the graphene-fluorographene interfaces. From the first principle calculations, the spins at the localized edge states are ferromagnetically ordered within each of the zigzag interface whereas the spin interaction across a nanoridge is antiferromagnetic. Magnetic susceptibility data agree with this physical picture and exhibit behaviour typical of quantum spin-ladder system with ferromagnetic legs and antiferromagnetic rungs. The exchange coupling constant along the rungs is measured to be 450 K. The coupling is strong enough to consider graphene with fluorine nanoridges as a candidate for a room temperature spintronics material.

Magnetic properties of carbon phases synthesized using high-pressure high-temperature treatment

Magnetic properties of carbon phases synthesized using high-pressure high-temperature treatment.

Unconventional Magnetism in Carbon Based Materials

Recently, a number of publications appeared in which reproducible observations of the roomtemperature ferromagnetic behavior of various carbon allotropes, such as graphite, fullerenes, microporous carbon and nanofoam were reported. Theoretical studies have shown that specific features of the electronic structure of carbon could give rise to ferromagnetic or superconducting correlations retained at high temperatures. This review collects the experimental studies of the carbon-based magnets and describes the current status of the theoretical work.

Pressure-induced ferromagnetism of fullerenes

Ferromagnetic behavior of polymerized fullerenes appears quite close to the boundary where the fullerene molecules are destroyed. However, when the presence of a disordered or graphitic phase is detectable by the standard characterisation methods, the ferromagnetic features quickly disappear.

Laser controlled magnetism in hydrogenated fullerene films

Room temperature ferromagnetic-like behavior in fullerene photopolymerized films treated with monatomic hydrogen is reported. The hydrogen treatment controllably varies the paramagnetic spin concentration and laser induced polymerization transforms the paramagnetic phase to a ferromagnetic-like one. Excess laser irradiation destroys magnetic ordering, presumably due to structural changes, which was continuously monitored by Raman spectroscopy. We suggest an interpretation of the data based on first-principles density-functional spin-unrestricted calculations which show that the excess spin from mono-atomic hydrogen is delocalized within the host fullerene and the laser-induced polymerization promotes spin exchange interaction and spin alignment in the polymerized phase.

Magnetic Properties of Polymerized Fullerene Doped with Hydrogen, Fluorine and Oxygen

Abstract We have presented recently a mechanism of ferromagnetism in polymeric fullerene phases based on spin and charge transfer from nonmagnetic donor or acceptor centers into fullerene molecules. In this work, the interaction between magnetic moments of the paramagnetic C60 R radical adducts (R=H, F, OH) dispersed in the 2D polymeric network is examined by using UB3LYP hybrid density functional method at 3‐21G level. The results show that the interaction is ferromagnetic, strong and long‐range.

Optical and vibrational properties of thin film Fullerene-Zn(II) tetraphenylporphyrin complexes

In this work a novel material, fullerene‐Zn(II) tetraphenylporphyrin, is obtained and studied using UV‐Vis‐NIR absorption and Raman scattering methods. C60–ZnTPP thin films were produced by vacuum evaporation in hot‐wall reactor. The detection of the Ag2‐derived modes at 1460 and 1452 cm−1 in the Raman spectra manifests the charge‐transfer C60–ZnTPP complex formation. It is shown that additional absorption band at 1.38–1.53 eV observed in the films corresponds to the HOMO‐LUMO gap of C60–ZnTPP complex.

Magnetic transition in the polymerized fullerene matrix

Abstract A mechanism of the ferromagnetism in the polymerized fullerene phase is proposed. We show that non‐magnetic defects and impurities give rise to a magnetic transition in the polymerized fullerene matrix. In our model, C60 molecules acquire spin and charge and become magnetically active due to the spin and charge transfer from non‐magnetic dopants. The interaction between magnetic moments of the arising paramagnetic species (C60 ± ions or C60 R radical adducts) dispersed in the polymeric network is inspected by using ab initio Hartree‐Fock and B3LYP hybrid density functional methods. It is revealed that the interaction is ferromagnetic and large enough for creating the high‐T c magnetism.