Ferromagnetism in Graphene Nanoribbons: Split versus Oxidative Unzipped Ribbons

Rao, Suchetha; Jammalamadaka, S. Narayana; Stesmans, André; Moshchalkov, Victor; Tol, Johan van; Kosynkin, Dmitry V.; Duque, Amanda L.; Tour, James M.

doi:10.1021/nl203512c

Cited by 96 publications

(93 citation statements)

References 51 publications

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“…From the exchange bias variation, a maximum value of H E ~ 52 Oe is observed when the GNRs were cooled with negative field of 1 kOe. On the other hand, previously, a maximum H E of 40 Oe has been observed upon cooling the GNRs with a positive field value of 4 kOe [19]. Our results are in accordance with the work done by Wu et.…”

Section: Resultssupporting

confidence: 94%

“…In our earlier work [19], we have reported that the low temperature susceptibility of the GNRs exhibits a peak at 70 K under the zero field conditions (ZFC), such a broad maximum has been correlated to the competing interaction between various FM and AFM magnetic phases. Such competing interactions lead to a negative EB upon positive field cooling.…”

Section: Resultsmentioning

confidence: 94%

“…Such magnetic, EB and the dynamic response of EB of potassium splitting of the multiwalled carbon nanotubes (GNRs) have been paralleled by experimental observations recently [19]. Possible sources for the observed ferromagnetism has been suggested from the clustering of magnetic fragments comprises of carbon defects coupled with hydrogen.…”

mentioning

confidence: 74%

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Influence of Negative Field Cooling on the Exchange Bias Properties of Potassium Split Graphene Nanoribbons

Narayana¹,

Singamaneni²,

Jammalamadaka³

2016

JMSE-A

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Abstract:We demonstrate the evidenced exchange bias properties of graphene nanoribbons (GNRs) with the negative magnetic field cooling. Upon the negative field cooling from 300 K to 5 K, the hysteresis loop shifts along the negative magnetic field axis, that coincides with the cooling field direction. This observation indicates that there exists a positive exchange bias in GNRs. Furthermore, enhanced exchange bias was observed when the polarity of field cooling is negative as compared with positive field cooling, hinting that there might be complex interplay between orbital and spin degrees of freedom. In addition, the variation of exchange bias and the coercive field as a function of negative cooling field is also studied.

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Section: Resultssupporting

confidence: 94%

Section: Resultsmentioning

confidence: 94%

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Influence of Negative Field Cooling on the Exchange Bias Properties of Potassium Split Graphene Nanoribbons

Narayana¹,

Singamaneni²,

Jammalamadaka³

2016

JMSE-A

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“…In analogy to our earlier HYSCORE work 38 on other GNRs, in addition to the proton hf interactions, the HYSCORE 13 C signals (in natural abundance) at low frequencies in Fig. 6 indicate 13 C hfc's are in the range |A( 13 C)| < 4 MHz (≈0.14 mT).…”

Section: Resultssupporting

confidence: 71%

Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

et al. 2014

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Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.

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“…31 Additional evidence is coming from magnetization and electron spin resonance experiments on unzipped graphene ribbons. 32 The sublattice degree of freedom plays a central role in the magnetic properties of bipartite lattices. [33][34][35] Very much like an external magnetic field favors one spin orientation and splits the spin states, an external perturbation favors one sublattice with respect to the other and opens a gap in the band structure of graphene.…”

Section: Introductionmentioning

confidence: 99%

Interplay between sublattice and spin symmetry breaking in graphene

Soriano

Fernández-Rossier

2012

Phys. Rev. B

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We study the effect of sublattice symmetry breaking on the electronic, magnetic, and transport properties of two-dimensional graphene as well as zigzag terminated one-and zero-dimensional graphene nanostructures. The systems are described with the Hubbard model within the collinear mean field approximation. We prove that for the noninteracting bipartite lattice with an unequal number of atoms in each sublattice, in-gap states still exist in the presence of a staggered on-site potential ± /2. We compute the phase diagram of both 2D and 1D graphene with zigzag edges, at half filling, defined by the normalized interaction strength U/t and /t, where t is the first neighbor hopping. In the case of 2D we find that the system is always insulating, and we find the U c ( ) curve above which the system goes antiferromagnetic. In 1D we find that the system undergoes a phase transition from nonmagnetic insulator for U < U c ( ) to a phase with ferromagnetic edge order and antiferromagnetic interedge coupling. The conduction properties of the magnetic phase depend on and can be insulating, conducting, and even half-metallic, yet the total magnetic moment in the system is zero. We compute the transport properties of a heterojunction with two magnetic graphene ribbon electrodes connected to a finite length armchair ribbon and we find a strong spin filter effect.

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Ferromagnetism in Graphene Nanoribbons: Split versus Oxidative Unzipped Ribbons

Cited by 96 publications

References 51 publications

Influence of Negative Field Cooling on the Exchange Bias Properties of Potassium Split Graphene Nanoribbons

Influence of Negative Field Cooling on the Exchange Bias Properties of Potassium Split Graphene Nanoribbons

Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

Interplay between sublattice and spin symmetry breaking in graphene

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