Nature - USA (2020-05-14)

Nature | Vol 581 | 14 May 2020 | 175

order upon self-intercalation, whereas their parental MX 2 bilayers are
nonferromagnetic. Notably, group V and group VI TMDs exhibit strong
ferromagnetism after self-intercalation (Fig. 4b). MX 2 bilayers that are
intrinsically ferromagnetic—that is, VX 2 , CrX 2 , MnX 2 and FeX 2 —retain
ferromagnetism upon self-intercalation (highlighted by orange trian-
gles in Fig. 4a). Among the 14 self-intercalated 2D ferromagnets that
we generated, the formation energies of 12 of these—the two excep-
tions being MoS 2 and MoSe 2 —were lower than or similar to those of the
non-intercalated materials (Supplementary Figs. 23, 24), indicating
that self-intercalation is energetically feasible.
To validate our theoretical predictions, we attempted to grow a
wide variety of ic-2D materials (Fig. 4a). In this figure, blue triangles

indicate that the self-intercalation can be experimentally realized^11 ,^12 ,

whereas grey triangles indicate that intercalation was not successful

under our experimental conditions. We succeeded in growing several

ic-2D crystals—namely V 11 S 16 (Fig. 4c, Supplementary Fig. 25), In 11 Se 16

(Fig. 4d, Supplementary Fig. 26) and FexTey (Fig. 4e, Supplementary

Fig. 27)—by either CVD or MBE. The topological features and corre-

sponding FFT patterns of these crystals are depicted in Fig. 4f–h. The

intercalated V 11 S 16 has a 2a × 2a superstructure, and the intercalation

concentration was estimated at 75% (Fig. 4f). In 11 Se 16 also showed a

2 a × 2a superstructure; however, in this case, the intercalated In atoms

reveal a signature honeycomb structure (Fig. 4g). The crystal structure

of self-intercalated FexTey was complicated—additional Fe atoms were

50%

0 PB

66.7%

0.016 PB 100% 0 PB

33.3%

1.46 PB

25%

17% 0.01 PB

0 PB

Ta intercalation, V (%)

20 40 60 80 100

0

0.4

1.6

Magnetic moment (

PB

) 1.2

0.8

–0.4

66.7%

0 PB

33.3%

0.39 PB

17%

0.43 PB

25%

0.69 PB

[100]

[010]

a

[010]

[001]

Ta

S

√ 3 a

Intercalated

Ta

S

S

b

0 100200300

T (K)

0.95

0.90

0.85

0.80

R (m

Ω cm)

c

Magnetoresistance (%)

d

Energy (eV) Energy (eV)

Rxy

(Ω

)

2

1

0

–1

–2

1.5 K 2 K

5 K 10 K

–2 –1 0– 1 2 2– 120 1

√ 3 a

e

f

gh

i j

2

1

0

–1

–2

B (T) B (T)

–10 –5 0510

1.2

0

0.4

0.8 10 K

1.5 K

2 K

5 K

dxy dyz dz 2 dxz dx (^2) –y 2 Spin-up dxy dyz dz^2 dxz dx^2 –y^2 Spin-down
–3
–2
–1
0
1
2
3
–3
Bilayer
Bulk
–2
–1
0
1
2
3
ΓΜΚΓΓΜΚ Γ
Fig. 3 | Ferromagnetism in Ta-intercalated Ta 7 S 12 ic-2 D cr yst al s.
a, Atomic-resolution STEM–ADF image of a typical self-intercalated Ta 7 S 12 film.
This image was collected using a half-angle range from about 30 mrad to 110
mrad to enhance the contrast of S. b, Optical microscopy image of a Ta 7 S 12 Hall
bar device encapsulated with hexagonal boron nitride. c, Resistivity of the
Ta 7 S 12 ic-2D crystal as a function of temperature. d, e, Temperature-dependent
magnetoresistance (d) and Hall resistance (Rxy) (e) of Ta 7 S 12 under an
out-of-plane magnetic field. f, Contour plot of charge density difference in
Ta - i n t e r c a l a t e d Ta 7 S 12. g, h, Orbital-resolved spin-up (g) and spin-down (h) band
structures of the intercalated Ta in Ta 7 S 12. i, Top view (top) and side view
(bottom) spin density isosurface of Ta-intercalated Ta 7 S 12. j, Calculated
magnetic moments as a function of the Ta-intercalation concentration (σ) in
2Ha-stacked nonstoichiometric TaxSy. μB, Bohr magneton. Scale bars: a, 0.5 nm;
b, 20 μm.