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Tabby graphene: Dimensional
magnetic crossover in uorinated
graphite
T. L. Makarova1,2, A. L. Shelankov2, A. I. Shames3, A. A. Zyrianova
4, A. A. Komlev
1,
G. N. Chekhova5, D. V. Pinakov5,6, L. G. Bulusheva5,6, A. V. Okotrub5,6 & E. Lähderanta1
Tabby is a pattern of short irregular stripes, usually related to domestic cats. We have produced Tabby
patterns on graphene by attaching uorine atoms running as monoatomic chains in crystallographic
directions. Separated by non-uorinated sp2 carbon ribbons, sp3-hybridized carbon atoms bonded
to zigzag uorine chains produce sp2-sp3 interfaces and spin-polarized edge states localized on both
sides of the chains. We have compared two kinds of uorinated graphite samples C2Fx, with x near
to 1 and x substantially below 1. The magnetic susceptibility of C2Fx (x < 1) shows a broad maximum
and a thermally activated spin gap behaviour that can be understood in a two-leg spin ladder model
with ferromagnetic legs and antiferromagnetic rungs; the spin gap constitutes about 450 K. Besides,
stable room-temperature ferromagnetism is observed in C2Fx (x < 1) samples: the crossover to a three-
dimensional magnetic behaviour is due to the onset of interlayer interactions. Similarly prepared
C2Fx (x ≈ 1) samples demonstrate features of two-dimensional magnetism without signs of high-
temperature magnetic ordering, but with transition to a superparamagnetic state below 40 K instead.
The magnetism of the Tabby graphene is stable until 520 K, which is the temperature of the structural
reconstruction of uorinated graphite.
Magnetism in restricted dimensions can be studied in real bulk crystals if the exchange interactions are much
stronger in one or two spatial directions than in the remaining ones1,2. us, low dimension magnets have the
advantage of bulk materials in providing sucient intensity for experiments investigating the thermodynamic
and spectroscopic characterization of magnetism. Most studies of low dimensional magnetism concentrate on
molecular magnets based on organic radicals (see e.g.3,4) or Cu and Ni compounds which have spins ½ or 1,
correspondingly5. We have recently synthesized a novel graphene derivative decorated by monoatomic uorine
chains running in crystallographic directions, and have observed clear signs of one-dimensional-like magnetism
in this two-dimensional material6. Nanoscale magnetic activity of pure graphene is controlled by the edge geom-
etry. In the present study, graphene uorination, instead of breaking of the carbon-carbon bonds, is used as an
ecient approach to generate edges and, therefore, correlated magnetic states in this material. e uorine chain
running in zigzag direction induces strong spin polarization with a mixed ferro-antiferro-magnetic coupling
between locally emerged magnetic moments.
A distinctive characteristic of the novel derivative is that the interfaces form Tabby stripes. Tabby is a pattern
of a cat’s coat with tiger stripes and leopard spots. Ideally, if the sp2-sp3 interfaces were parallel and evenly spaced
lines, they would form embedded graphene nanoribbons. e stoichiometry C4F yields a 3-carbon atom wide
nanoribbon, C3F is a 2-atom wide one, and C2F produces monoatomic chains (Fig.1a). However, this ideal pic-
ture is only partially applicable, because the stripes run in all crystallographic directions (Fig.1b). Still, the Tabby
graphene is a unique derivative because the retention of the π-electron system results in dierent electronic
properties of the Tabby graphene compared to fully functionalized graphene derivatives, which are insulators.
e Tabby graphene contains conned islands of the π-electron system, it is semiconducting with the band gap
2–2.5 eV, and colour dependent on the C/F ratio7. e most distinct feature is that the Tabby graphene contains up
1Lappeenranta University of Technology, Lappeenranta, 53851, Finland. 2Ioe Institute, St. Petersburg, 194021,
Russian Federation. 3Ben-Gurion University of the Negev, Be’er-Sheva, 8410501, Israel. 4St. Petersburg State
University, St. Petersburg, 199034, Russian Federation. 5Nikolaev Institute of Inorganic Chemistry SB RAS,
Novosibirsk, 630090, Russian Federation. 6Novosibirsk State University, Novosibirsk, 630090, Russian Federation.
T. L. Makarova is deceased. Correspondence and requests for materials should be addressed to E.L. (email: Erkki.
Lahderanta@lut.)
Received: 29 June 2017
Accepted: 8 November 2017
Published: xx xx xxxx
OPEN
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
to 10% of stable unpaired spins on carbon atoms. ese states interact antiferromagnetically or ferromagnetically,
depending on sublattice position.
We implemented the zigzag edge states at sp2-sp3 interfaces by slow uorination of graphite intercalation
compounds, which expanded into graphenes during the synthesis. is approach allowed us to obtain single-
or bi-layers of uorinated graphenes. In the case of the fully uorinated graphene CF, all π-electrons on the
basal planes were spent for covalent bonding with uorine8, whereas decient uorination (Fig.1) preserved
the π-system partially, and its electronic properties were sensitive to the uorine coverage9,10. Spin-half Curie
paramagnetism in graphene functionalized with fluorine has been observed previously11. Quite recently, a
ferromagnetic-like response has been found in hydroxouorographenes and interpreted as due to biradical
states12.
In this paper, we report on data demonstrating that the π-electron network in carbon nanosegments formed
by Tabby uorine patterns on the basal planes, shows non-Curie paramagnetism and magnetic order, depending
on the stacking of graphitic planes and the uorine coverage. We concentrate on similarities and dierences in the
magnetic properties of the Tabby graphene for various uorine contents.
Results
Magnetic properties of Tabby graphene C2Fx with x < 1. e magnetic properties of Tabby graphenes are
tightly connected with their structure, which changes during the sample history. Immediately aer the synthesis, the
samples were diamagnetic with only a Curie-like paramagnetic tail at low temperatures13. Unexpectedly, the meas-
urements performed in several months, during which the samples were stored in a desiccator at room temperature,
revealed qualitative changes: in addition to spin-half paramagnetism (Fig.2a), the magnetic susceptibility as
a function of temperature exhibited a maximum at ~250 K (Fig.2b). e contribution of this non-Curie para-
magnetism increased during further ageing (Fig.2c), and in about one year the broad maximum followed by an
activation-like drop on cooling (Fig.2d) became a dominating feature in the magnetic susceptibility. Remarkably,
the magnetization increased by 50 times aer one year of storage.
The linear magnetic susceptibility χ(T) in Fig.2 can be split as χ = χ0 + χCurie + χspin into a
temperature-independent term χ0, a small Curie-like part χCurie = C/T identified by the low-T upturn,
and a spin contribution χspin. e term χspin(T), that is the nontrivial part of the magnetic response, shows a
non-monotonous temperature dependence with a broad maximum. is feature cannot be understood in the
frames of independent magnetic moments. As shown in Fig.2, non-monotonous temperature dependence of
magnetic susceptibility χspin is the hallmark of low dimensional magnetism and is typical for both chain- and
ladder-structured materials14. e position of the maximum in the plot of χspin (T) establishes an energy scale
related to the strength of antiferromagnetic (AF) spin-spin interaction which favours spin pairing, and therefore,
opposes the spin alignment parallel to an external magnetic eld15.
To extract the strength of the interaction from the data and to estimate the amount of interacting spins, one
may think in terms of localized spins with the Heisenberg Hamiltonian, H = Σij Jij Si·Sj where Si is the spin located
at site i and Jij denotes the strength of the exchange interaction. As in the case of molecule-based materials, various
models can be tried out: the Heisenberg chain with anisotropic antiferromagnetic coupling (Bonner-Fisher16),
the Hateld model17 of a 1D spin chain with modulated coupling, a dimerised chain (Bleaney-Bowers18), and a
spin ladder with antiferromagnetic interactions (Troyer-Tsunetsugu-Würtz19). However, none of these models
which assume various modications of only antiferromagnetic couplings, could give satisfactory agreement with
our experiment. Indeed, the picture of the spin interactions that was predicted by the discoverers of the peculiar
edge states of zigzag graphene nanoribbons in the seminal work by Wakabayashi et al.20, is characterized by
ferromagnetic exchange coupling JFM ~ 103 K within a zigzag edge and an antiferromagnetic edge-edge coupling
of the order JAFM ~ 10–100 K, depending on the nanoribbon width21. It is therefore reasonable to interpret the
experimental results in the frames of the spin ladder model with ferromagnetic legs (JFM) and antiferromagnetic
rungs (JAFM). We calculated the magnetic susceptibility of this model for the number of spins in a leg, Ns, changing
Figure 1. Basal plane of deciently uorinated graphene: (a) Embedded nanoribbons; (b) Tabby pattern is
plotted according to the results of spectroscopic investigations7,28,29. e blue circles denote carbon atoms, and
the yellow circles denote uorine atoms.
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
from 1 to 126, and found that this model could be used successfully to t a large batch of samples. As an example,
the solid line in Fig.2d corresponds to a combination of Ns = 3 and Ns = 8.
On the basis of the analysis of the susceptibility curves obtained on the dierent samples, we have arrived at
the following quantitative conclusion: (i) with the maximum at T = 200–280 K, the exchange interaction strength
(JAFM) value is in the range JAFM = 300–450 K22; (ii) the concentration of the exchange-coupled spins is rather large,
being in the range 1–20% per CnF structural unit; (iii) the residual concentration of isolated spins ½ does not
exceed 0.1%. e JAFM value conrms quantitatively that the AFM interactions within the graphene planes are
much stronger than those in the organic radical crystals (e.g. nitroxide-based radicals, verdazyl radical crystals,
or thiazyl radicals3), making the Tabby graphene an ideal candidate for 2D behaviour studies of pure organic
materials.
Evolution of the magnetism of C2Fx (x < 1) on ageing and annealing. A remarkable property of
the Tabby graphene is the development of macroscopic magnetic order during ageing. Figure3a shows that the
behaviour of as-prepared samples is accurately described by the Brillouin function, which provides a good t
for total angular momentum quantum number J = S = ½ (free isolated electron spin). e saturation value in
the magnetization curve shown in Fig.3b corresponds to 0.3% of localized spins participating in the long-range
magnetic order.
As the samples were purely organic, their magnetism was prone to thermal eects. We observed a sharp drop
of paramagnetic response (Fig.3c,d) and saturated magnetization (Fig.3e) as a result of short-term heating up to
the uorine detachment temperature (520 K). is conrms that the magnetism of the Tabby graphene has pure
organic origin and is determined by the uorine arrangement on the basal plane.
We made an attempt to determine the Curie temperature for this organic magnet by measuring the isothermal
M(H) loops and plotting the saturated magnetization at each temperature point (Fig.3f). e Curie temperature
was higher than the room temperature, but its exact value could not be determined because the magnetism falled
irreversibly due to thermal destruction of the samples.
Magnetic properties of C2Fx with x ≈ 1. e Tabby graphenes of the composition C2Fx (x ≈ 1) were
prepared by using similar technological procedures as in the case of C2Fx, x < 1 (see the supplementary infor-
mation for more details). All samples were Curie-like paramagnetic at room temperatures without any sign of
ferromagnetism. However, on cooling, a strong increase in the magnetic moment was observed, pointing out
at a ferromagnetic-like transition near 40 K (Fig.4a). is transition was registered by both Superconducting
Quantum Interference Device (SQUID) and Electron Paramagnetic Resonance (EPR). e double integrated
intensity (EPR susceptibility) followed the ZFC magnetization protocols. e zero eld–cooled (ZFC) and the
eld-cooled (FC) magnetizations diverged below 16 K, indicating a slow relaxation (blocking) of magnetization
(Fig.4a). is low-temperature behaviour was sensitive to the applied magnetic elds (H), and at H = 1000 Oe
the dierence between the ZFC and FC magnetizations was undetectable (Fig.4c). e position of the shis to
lower temperatures as the eld increased, yielding the anisotropy eld HA = 2600 Oe and a zero-eld value of
the blocking temperature, T0max = 10.5 K. M(H) isothermal dependencies (Fig.4d), conrmed that below 40 K
we observed superparamagnetism, and the numerical ts of the data in Fig.4c,d give an average spin quantum
number S ≅ 1000.
Keeping the samples at room temperature for a year caused strong changes to the magnetic response (Fig.4b).
e magnetism of the aged samples looked similar at rst glance, but really it was not. First, the values of mag-
netic moment below the ferromagnetic-like transition were 40–50 times smaller in the aged samples. Second,
on cooling from room temperature, the magnetic susceptibility passed through a maximum around 280 K and
approached zero at low temperatures. is indicates clearly that the temperature dependence of magnetic sus-
ceptibility exhibits an activated behaviour below a broad maximum, which is characteristic of thermal excitation
from a nonmagnetic ground state with a spin gap. Annealing the samples in a dynamic vacuum at T = 373 K for
24 hours resulted in full restoration of the magnetic properties shown in Fig.4a. is resulted in the reduction
of the oxygen and water content from 0.47% to 0.19%, and from 1.21% to 0.75% correspondingly, as veried by
X-ray photoelectron spectroscopy. is led probably to the increase of interlayer interactions and development
of 3D superparamagnetic ordering below 40 K. Apparently, both oxygen and water pushed the graphene planes
apart, and the magnetic response was dominated by short-range 2D antiferromagnetic interactions.
Figure 2. Evolution of magnetic susceptibility vs. temperature upon ageing of C2Fx (x < 1): (a) A Curie-like spin
magnetism observed in as prepared samples; (b) and (c) progressive changes aer few months of storage; (d)
aer 1 year.
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
EPR study of C2Fx with x ≈ 1. e EPR technique, which allows selective tracking of dierent magnetic
entities, diagnoses the magnetic units responsible for the described phenomena. For all the studied samples, the
room temperature EPR spectra revealed two main constituents: (a) narrow lines within the region of g = 2.00,
typical for uorinated carbon, and (b) asymmetric broad lines with g ~ 2. e total spin densities were found
to be 1018–1020 spin/g with only 1–2% contribution coming from the narrow signals. We focused the attention
on the broad lines. For all samples, doubly integrated intensities for the broad lines which corresponded to EPR
susceptibility followed the trends for SQUID susceptibility (see Fig.4a,b), while the dierences between the FC
and ZFC measurements followed the shi of the resonant eld positions Hrbroad. At each temperature, the position
of a broad EPR line (i.e., resonant eld Hrbroad) for this paramagnetic entity was determined by the origin of the
entities (g-factor) and the internal magnetic elds (like hyperne one etc.). us, the developing temperature shi
of Hrbroad manifested progressive strengthening of the internal magnetic eld. It is worth mentioning here that the
resonant eld of the narrow EPR line, attributed to uorinated carbon, remained the same within the entire tem-
perature region of 4–300 K. is may have reected both the inhomogeneity of the samples and the local nature
of magnetic ordering in the corresponding entities.
An unambiguous attribution of the magnetic unit can be done for as-prepared C2Fx (x ≈ 1). ere we observed
clear transformation of the same broad EPR signal that was observed at room temperatures, into a multicompo-
nent ferromagnetic resonance (FMR) signal (Fig.5). Below 40 K the broad EPR signal grew abruptly in integral
intensity, broadened and then split into low and high eld components, which shied towards opposite directions
on further temperature decrease. e low eld component kept shiing to the zero eld region and then disap-
peared below 25 K, whereas the high eld component at T = 15 K turned back to lower resonance eld values, still
remaining within the high eld region (Fig.6c). All the above features are typical for ferromagnetic (FMR) sig-
nals originated from partially oriented ferromagnetic subsystems with dierent magnetic anisotropies. us, the
Figure 3. Evolution of the ferromagnetic properties of the Tabby graphene C2Fx (x < 1) upon ageing and
annealing: (a) magnetic moment M as a function of a magnetic eld H; the symbols are the measurements
and the solid curve ts the Brillouin function with S = ½ and g = 2; (b) M(H) dependence of the same sample
aer 1 year of ageing at room temperature. e temperature dependences of the magnetic susceptibility of the
aged sample; (c) the same sample aer short-term heating to the uorine detachment temperature 520 K (d).
M(H) dependence of an aged sample and the same sample aer short-term heating to 520 K (e). Temperature
dependence of the saturation magnetization Ms for the Tabby graphene; the sharp decrease of Ms around 400 K
is due to the beginning of thermal irreversible destruction of the sample (f).
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
subsystem of exchange-coupled magnetic entities responsible for the short-range in-plane interactions, was also
responsible for the ferromagnetism observed in these systems at low temperatures. is subsystem was present
in all the studied samples: as-prepared, aged and annealed. Its magnetic behaviour was rich: it demonstrated 2D
antiferromagnetic interactions, room temperature magnetic ordering, and the development of low-temperature
superparamagnetism. We note that superparamagnetic behaviour below 25 K have been observed in EPR studies
of nanosized graphite prepared by ball milling23 and of ultrathin graphitic particles obtained by heavy sonication
of graphite powder24.
In the case of Tabby graphenes C2Fx with x < 1, the position of the broad line, Hrbroad, was shied to the low
eld region and changed its position smoothly on cooling. is indicates a decrease of an internal spontaneous
Figure 4. Temperature dependencies of magnetic susceptibility for Tabby graphenes, C2Fx (x ≈ 1): (a) pristine
samples; (b) aged samples – the open circles represent the ZFC, the solid circles are the FC measurements, the
red symbols represent the double integrated intensity (the EPR susceptibility); (c) M(T) curves taken at dierent
elds; (d) M(H) dependencies taken at dierent temperatures.
Figure 5. Temperature dependence of EPR spectra for the as prepared Tabby graphene, C2Fx (x ≈ 1) at
T < 100 K. All spectra were recorded at the same experimental conditions: ν = 9.469 GHz, incident microwave
power 20 mW, 100 kHz magnetic eld modulation amplitude 0.5 mT, and receiver gain 104. e spectra have
been shied vertically for better presentation. e dashed arrows indicate changes in Hrbroad for low- and high-
eld components of the FMR signal at decreasing temperature.
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
magnetic eld (Fig.6a). For the case of Tabby graphenes with x < 1, the same behaviour of Hrbroad was observed
within the temperature range of 100–300 K. However, below 100 K, the Hrbroad in this sample shied abruptly to
the higher eld region (Fig.6b corresponds to the sample depicted in Fig.4b), indicating signicant change in the
internal magnetic eld on cooling.
Discussion
Fluorination is well known to be an eective method for introducing localized spin centres into graphene. When
the attached uorine atoms are arranged as monoatomic chains running in crystallographic directions (Tabby
pattern), the sp2-sp3 interfaces created by the uorine chain play the same role as zigzag edges. e graphene
bipartite lattice consists of inequivalent A and B sublattices. In the case of a zigzag chain, one expects a set of local-
ized spin states in sublattice A on one side of the nanochain and sublattice B on the other side. Density functional
theory (DFT) calculations for well-separated uorine chains clearly reveal the emergence of magnetism in uori-
nated graphene6. e calculated complex magnetic conguration combines the strong ferromagnetic interaction
between the local magnetic moments of C atoms within each side of the CF chain with the antiferromagnetic
coupling between the magnetic moments of C atoms located on the opposite sides of the CF chain.
The parallels in the magnetic behaviour of Tabby graphenes with different stoichiometry and stacking
sequences lead to a conclusion that the magnetic unit responsible for the ordering eects originates from the
π-electron system in the nanosegments created by the Tabby patterns with the magnetic moments localized at the
zigzag interfaces. DFT calculations conrm that edge states near a single zigzag chain are preserved in disordered
networks of densely packed interfaces6. Strong dierences in the magnetic behaviour of the described samples are
explained by their structural dierences.
Several graphene derivatives are known, e.g. graphene oxide, hydrogenated graphene, uorographene, and
chlorographene. Functionalization opens the band gap of graphene, which is desirable for on/o electronics.
However, at full graphene coverage, the possibilities for manipulation of electronic properties are limited because
the π electrons are already spent to the attached atoms. Extensive studies are done on releasing the π electrons by
producing single-side C2F and C2H (still not synthesized), or “digging” the wide-gap derivatives, removing extra
atoms and forming one-dimensional graphene regions: point defects, quantum dots, nanoribbons, superlattices.
In the synthesis of the Tabby graphene, the method of slow uorination provides conditions where adsorb-
ates tend to align in a chain sequence in which F adatoms are located on alternating sides of the graphene plane.
Fluorine has the highest electronegativity of all elements. If the synthesis is made slowly at low temperature,
quasi-equilibrium conditions allow uorine to attach to the thermodynamically preferable places. Fluorinated
carbon tends to separate spatially from non-uorinated carbon. If one F is attached to the graphene, the next F
will most preferably attach close to it, to another side in the ortho-position. e adsorption of an odd number of
F atoms disturbs the π-electron system, so the adjacent atom attaches as close as possible, but to another side due
to strong repulsion. e meta-position is unfavourable because it creates unpaired radicals.
We observed 2D spin gap -activated magnetism of C2Fx (x < 1) samples aer prolonged ageing (Fig.2). It can
be speculated that this feature is related to the bilayer-like structure of uorinated graphite (x < 1). During the
Figure 6. Resonance eld positions Hr of the EPR signal vs. temperature for Tabby graphene C2Fx: (a) uorine
content x < 1; (b) aged sample with x ≈ 1; and (c) the same sample with x ≈ 1 as prepared.
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Scientific REPORTS | 7: 16544 | DOI:10.1038/s41598-017-16321-5
gas-phase synthesis, simultaneous F adsorption at multiple sites resulted in seeding of the chains in a random dis-
tribution across the graphene planes. Apparently, the chains were not long enough to produce the zigzag-inherited
edge states. e honeycomb lattice of graphene is a bipartite lattice. Sublattices A and B are identical in a single
layer. In a bilayer, atom attachment on B sites is energetically more preferable than on A sites. e chain grown in
a certain direction of a graphite layer may dictate the rule for the pattern formation in the adjacent layer. e C−F
bonds in graphene are dynamic, with a low energy barrier for the migration of F atom to the nearest C atom. e
uorine chains repeal and arrange in two neighbouring layers like the teeth of a comb. is creates an additional
discriminating mechanism leading to the formation of regular Tabby patterns where crossing and branching are
suppressed, which is presumably favourable for magnetic coupling.
When the layers in the Tabby graphene are substantially spaced, as in C2Fx (x ≈ 1), the compound can be
considered as a stack of monolayers. In this case the discriminating mechanism for chain formation is absent.
Although uorination does produce localized spins, the chain length is not enough for the development of zigzag
edge states with measurable magnetic interactions on the 2D plane, or the development of high-temperature
long-range magnetic ordering. High-temperature long-range magnetic ordering was absent in the samples of our
study. Instead, we observed transition to 3D superparamagnetic behaviour at low temperatures. A low tempera-
ture ferromagnetic transition was seen in the multicomponent FMR signal, with the features typical for partially
oriented ferromagnetic subsystems having dierent magnetic anisotropies. Ageing of the samples led to 50-fold
reduction in the 3D magnetism, whereas transition to 2D behaviour was detected from the broad maximum and
low-temperature activated behaviour of magnetic susceptibility.
To sum up, uorination of graphene in such a way that the attached uorine atoms formed monoatomic
stripes running in crystallographic directions produced a special type of graphene derivative, which we call the
Tabby graphene. e sp2–sp3 interfaces produced by the uorine atoms attached in the zigzag directions gave rise
to numerous magnetic phenomena. Graphene is a two-dimensional material, whereas the uorine chain patterns
reduce the eective dimensionality to 1D. Magnetic susceptibility shows a behaviour typical for low-dimensional
quantum spin-ladder systems, which is characterized by spin ordering along the zigzag edges and their antipar-
allel alignment between opposite zigzag edges. e existence of a gap in the spin excitation spectra of graphene
ribbons with zigzag edges has been theorized since their discovery in 1998. We produced magnetically active
uorinated graphite samples and showed that this type of low-dimensional magnetism can be realized experi-
mentally in a graphene-based system. We observed magnetic dimensional crossover with changes in the uorine
loading and interlayer distance, the parameters that can be controlled by synthesis conditions, sample ageing, and
annealing. e Tabby graphene is a promising material with tuneable electronic and magnetic properties, and it
provides a playground for the exploration of new quantum many-body states as well.
Methods
Sample preparation. Samples of uorinated graphite C2Fx with the uorine content x, 0.5 ≤ x ≤ 1, were
produced by room temperature synthesis25–27. e starting material for the synthesis of the uorinated graphite
samples was natural graphite from the Zaval’evo deposit (Ukraine). To remove metal and silicate impurities, the
material was puried by double acid treatment (HNO3:HCl 1:3 and concentrated HF). e grain size of the sam-
ples was about 100 × 100 × 20 μm, and the content of 3d metal impurities was below 1 ppm. Detailed description
of sample preparation can be found in Supplementary Information.
Characterization methods. DC magnetic measurements were performed at a Quantum Design SQUID
magnetometer (MPMS-XL-1) in −1 T–+1 T magnetic elds. e DC magnetic susceptibility data were collected
in the 1.76–400 K range in a 10 mT magnetic eld. Electron Paramagnetic Resonance (EPR) measurements
within the temperature range 4 K < T < 300 K were carried out by using a Bruker EMX-200 X-band (ν~9 GHz)
EPR spectrometer equipped with Oxford Instrument ESR900 cryostat and Agilent 53150 A frequency counter at
microwave power (PMW) levels ranging from 50 µW to 200 mW. e structure and composition of the uorinated
graphite samples were studied by means of X-ray diraction (XRD) on a DRON-SEIFERT-RM4 diractometer by
using CuKα radiation and X-ray photoelectron spectroscopy (XPS) on a Phoibos 150 SPECS spectrometer using
monochromatized AlKα radiation with the energy of 1486.7 eV. e results of structure and composition analysis
are given in Supplementary Information.
Data availability statement. All data generated or analysed during this study are included in this pub-
lished article (and its Supplementary Information les).
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Acknowledgements
is research was supported by the Russian Science Foundation (Grant #14–13–00813) and European FP7 IRSES
project 295180 MagNonMag. We are grateful to Dr I.P. Asanov for the XPS measurements and Dr Yu. V. Shubin
for the XRD patterns.is study has been performed in the research group of Tatiana Makarova. Fighting with
her illness, Tatiana was able to prepare the rst version of the manuscript, working to the very last hours of her
life. We, colleagues and friends of Tatiana, will miss her warm personality and highest expertise in physics.
Author Contributions
T.L.M. designed and carried out most of the experiments. A.L.S. and L.G.B. performed the theoretical
modelling. Interpretation of the results was done by T.L.M. and A.L.S., with important contribution from A.I.S.
and E.L. Sample preparation was done by G.N.C. and D.V.P., whereas A.V.O. and L.G.B. provided structural
characterization. A.I.S. performed the EPR study. K.A.A. and A.A.Z. contributed to the SQUID magnetic
measurements. T.L.M. wrote the main part of the text with the contribution of all the authors. All authors
discussed and reviewed the results.
Additional Information
Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-017-16321-5.
Competing Interests: e authors declare that they have no competing interests.
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