Room temperature p-orbital magnetism in carbon chains and the role of group IV, V, VI, and VII dopants

Abstract

The study of magnetism without the involvement of transition metals or rare earth ions is considered the key to the fabrication of next generation spintronic devices. Several recent reports claim that optimizing the occupation number of the mixed p-orbitals is the correct way to reinforce p-orbital magnetism in bulk crystals. We provide experimental evidence that the kinked monoatomic carbon chains, the so-called linear-chained carbon, generate intrinsic ferromagnetism even above room temperature. According to our ab initio calculations, unconventional magnetism has its origin in the p-shells. In contrast, the linear monoatomic carbon chains are non-magnetic. Although the optimized differential spin density of states at the Fermi level (SDOS) of the kinked carbon chains is higher than that of bulk Fe, the magnetic moment is as low as 0.3μB. In order to enhance the magnetic response, we decided to tune the p-orbital magnetism by adding dopants from groups IV to VII of the periodic table. We observed that the strength of the p-orbital magnetism and the sign of the exchange interaction depend not only on the kink angle, but also on the concentration of lone pair electrons, free radical electrons, lateral chain spacing, internal electric dipole, dative covalent bonds and the Bohr radius of the dopants. Surprisingly, the V and VII-doped carbon chains show a strong non-zero SDOS, which has its origin in the p-shells. The VII-doped carbon chains give the SDOS of the opposite sign. Our best system, the arsenic-doped carbon chain, exhibits a strong local magnetic moment of 1.5μB, which is comparable to that of the bulk Fe of 2.2μB, with the mean exchange-correlation energy reaching a 63% ratio relative to that of the bulk Fe.

X-ray Photoelectron Spectra of Ag-Au Colloidal Nanoparticles after Interaction with Linear Carbon Chains

“…In particular, it was shown that one-dimensional carbon chains can have a strength, elastic modulus, and stiffness greater than any known material, including diamond, carbon nanotubes, and graphene, and make it possible to create new composite materials [22]. It is also assumed that carbines can be used to create field-effect transistors [25], and also show the possibility of possessing one-dimensional carbon chains with interesting magnetic [26] and electrical properties [27,28].…”

Enormous enhancement of p-orbital magnetism and band gap in the lightly doped carbyne

“…Although the magnetic moment of p-shell may be weak [6], the electrons that move less freely on p-shells allow a strong exchange coupling [5]. An experimental observation confirmed that the p-orbital ferromagnetism of the undoped monoatomic carbon chain persisted up to 400K, even though the magnetic moment of carbon is only ~0.2µ B [5].…”

“…A. Bergara et al have verified that the optimized magnetic moment of the p-shell corresponds to a maximum overlap between the p-shells [1]. If the orbitaloverlap is too strong, the circulation motion of the electron is disturbed by a strong electrostatic repulsion which destroys the magnetic moment of p-shell [1,5].…”

“…Although carbon materials do not contain electrons in d-shells, the circular motion of the electrons can activate p-orbital magnetism when the p-orbits effectively overlap [1,2,3]. The disappearance of orthogonal interaction in a one-dimensional system allows the resulting orbital overlap of pshells concentrating on the chain axis, so that the p-orbital magnetism is more favorable in a one dimensional structure [1,4,5]. An early investigation on the monoatomic lithium or sodium nanowires showed that the strength of p-orbital ferromagnetism depends on the bond length and the bond angle [1,4].…”

Toward the Synthesis of Highly Processable Long-Chain Carbyne Using Multilevel Pulse Injection

“…Journal of Nanomaterials needed for carbyne production [8]. Thus, the proposed mechanism sought to satisfy these four essential conditions without the use of CNTs, suggesting a possible route toward highly processable long-chain carbyne.…”