Theoretikal investigation of contact-induced phenomena in composite materials containing fullerenes and nanotubes deposited on ferromagnetic substrates

Abstract

The interfaces of armchair and zigzag carbon and boron nitride nanotubes with ferromagnetic Co(0001) and Ni(111) surfaces was investigated by first-principles calculations. The electronic structure analysis reveals the presence of contact-induced spin polarization in all composites. It was found that NT(n,0)/Co composites are approximately twice as low in energy as NT(n,0)/Ni ones and spin polarization in these systems is also much stronger. Lower energy of CNT(9,0)/TM in comparison with CNT(10,0)/TM can be attributed to the difference in their conducting properties. Conducting nature of CNT(9,0) also causes a weaker spin polarization in comparison with other tubes. In addition, BNNTs demonstrate a local contact-induced conductivity while the fragments distant from interface remain to be insulating. Value of spin polarization differs significantly from one possible configuration of composite to another for armchair nanotubes. Unfortunately, for all considered systems there is almost no difference in energy among the variants of nanotube and metal substrate mutual arrangement. This makes their utilization in spintronics unreasonable, in contrast with previously studied zigzag nanotubes [8]. However, contact-induced local conductivity in boron nitride nanotubes still can be used somewhere in nanoelectronic devices. Particularly, their high thermal conductivity along with abovementioned unique electronic properties allows using them in thermoelectric coolers based on the Peltier effect. Density functional study of atomic and electronic structure of C60/Fe(100) composite shows the coexistence of a number of possible structures with strong chemical bonding between composite compartments. Fullerene and slab deformation plays an important role in the formation of composites. Low potential barriers of fullerene’s relocation witness the possibility of transitions between stable structures which are almost equally probable according to the Gibbs distribution. Average charge transfer and magnetic moment on C60 molecule remain virtually the same within the range of 250–350 K, opening possibility of using such composites for quantum computing or other applications. Many possible structures were also found to co-exist for LSMO/C60 nanocomposites in wide range of temperatures. Only spin polarization at Fermi level was found to depend strongly on the configuration while both C60 charge and magnetic moment remain virtually the same. However, spin-polarized transport is still possible even for less favorable configurations. Manganese atoms play a key role in binding between fullerene and LSMO which is confirmed by the values of binding energies and spatial spin density distribution patterns. The mechanism of spin-polarized charge transport was discussed. According to our analysis of magnetic moment values and spin density spatial distribution, it’s evident that this is due to the special kind of magnetic ordering in C60 molecule rising from the interaction with manganese atoms and complex magnetic exchange interaction. The interaction with LSMO(Sr-O) slab changes the electronic structure of the tubes noticeably. However, this change is mainly due to the deformation of the tubes, not the interaction with the substrate. The electronic structure of LSMO remains unchanged, and only a weak van-der-Waals interaction is responsible for the composite formation. In contrast to the Sr-O terminated surface, there is a visible interaction between CNT(5,5) and Mn-O terminated LSMO. Overlapping between carbon and manganese atoms plays a key role in composite formation, in agreement with results obtained for C60 [116]. Regardless the major deformation of nanotubes when interacting with LSMO, the composite formation is energetically favorable in all cases.