Magnetic Fullerenes inside Single-Wall Carbon Nanotubes

Abstract

C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C59N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of spin-lattice relaxation time, T1, of C59N indicates a reversible charge transfer toward the host nanotubes above ∼ 350 K. Bound C59N-C60 heterodimers are formed at lower temperatures when C60 is co-encapsulated with the functionalized C59N. In the 10-300 K range, T1 of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.Single-wall carbon nanotubes (SWCNTs) [1, 2] exhibit a variety of unusual physical phenomena related to their one-dimensional and strongly correlated electronic properties. These include excitonic effects [3,4], superconductivity [5], the Tomonaga-Luttinger liquid state [6], and the Peierls transition [7]. Magnetic resonance is a powerful method to study strong correlations in low dimensional systems. However, for SWCNTs both nuclear magnetic resonance (NMR) and electron spin resonance (ESR) are severely limited by NMR active 13 C nuclei and ESR active electron spins in residual magnetic catalytic particles and other carbon phases. Synthesis of 13 C isotope engineered SWCNTs solved the problem for NMR [8,9]. To enable ESR spectroscopy of SWCNTs, a local probe, specifically attached to SWCNTs, is required. The N@C 60 [10] and C 59 N [11] magnetic fullerenes are ideal candidates for such studies. In fullerene doped SWCNTs, fullerenes occupy preferentially the interior of the tubes and form "peapods" (C 60 @SWCNT) [12]. Fullerenes adhesing to the outside can be removed [13] in contrast to e.g. filling with iron [14]. ESR on encapsulated magnetic fullerenes could yield information on the electronic state of the tubes and it could also enable to study the fullerene rotational dynamics in a confined environment. In addition, magnetic fullerene peapods could exploit the combination of the SWCNT strength and the magnetic moment of molecules in magnetic scanning probe tips and they could enable a bottom-up design for magnetic storage devices or for building elements of quantum computers [15].Typical spin concentrations in (N@C 60 :C 60 )@SWCNT are low, ∼1 spin/tube, and the N spins are insensitive to SWCNT properties [16]. The C 59 N monomer radical is a better local probe candidate as the unpaired electron is on the cage. C 59 N can be chemically prepared but it forms spinless dimers (C 59 N) 2 or monomer adducts [11].The magnetic C 59 N monomer radical can be stabilized as C 59 N:C 60 , a dilute solid solution of C 59 N in C 60 [17].Here, we report on the first ESR study of SWCNT properties and peapod rotational dynamics using a paramagnetic local probe: C 59 N monomer radicals encapsulated inside SWCNTs. SWCNTs were first filled with chemically inert C 59 N derivatives. A heat treatment in vacuum removes the side-group and the monomer radical is left behin...

Enhanced thermal stability and spin-lattice relaxation rate of N@C60inside carbon nanotubes

“…As we show below, this holds down to the lowest temperatures. It is interesting to note here, that a similar situation was encountered for another diluted magnetic fullerene peapod system, the C 59 N:C 60 , where the rapid T 1 relaxation causes a homogeneous broadening [17].…”

“…The eight voids between the fullerenes and the host nanotube wall are significantly smaller than the so-called octahedral and tetrahedral voids in crystalline C 60 . This, combined with the hindered rotation of the fullerenes [17], probably limits the above described escape process of nitrogen simply by geometrically limiting the available room for the above described swinging-out process. For both mechanisms, the Gaussian distribution of tube diameters with an average of 1.4 nm and 0.1 nm variance explains why the thermally induced decay of N@C 60 is spread out in temperature: we expect that both the electronic modification of the fullerenes through the fullerene-nanotube interaction and also the geometrical effect are strongly influenced by the diameter of the host tubes.…”

“…Peapods with magnetic fullerenes can be used to study the electronic properties of the tubes [17] and may be suitable for quantum information processing [18,19] and they are thought to be good candidates for magnetic force microscopy cantilevers. The endohedral N@C 60 fullerene is itself a unique molecule as it contains an atomic nitrogen in the electron spin S=3/2 configuration [20].…”

Assembly of Cobalt Phthalocyanine Stacks inside Carbon Nanotubes

“…[9,10] Magnetic effects have been observed recently in the encapsulation of azafullerene (C 59 N). [11] Similarly, from the metallic point of view, both cobaltocene and ferrocene have been successfully encapsulated in nanotubes. [12,13] For both these molecules a strong interaction with the nanotubes is observed, resulting in electron doping of the nanotubes, which is confirmed by density functional calculations.…”

Raman scattering from nanomaterials encapsulated into single wall carbon nanotubes

“…37 When the functional group was split off by heating after the molecule was filled into the tube, a magnetic molecule was retained. 38 However,…”