Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

Abstract

We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe 0.25 TaS 2 . The vdW interlayer coupling at the Fe-intercalated plane of Fe 0.25 TaS 2 allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material through the vdW junction.*E-mail: moriyar@iis.u-tokyo.ac.jp; tmachida@iis.u-tokyo.ac.jp 2 Recently, studies on two-dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN), and transition metal dichalcogenides (TMDs) have received considerable attention [1,2]. These materials exhibit layered structure in the bulk form, and the van der Waals (vdW) force connects each of the layers. Thus, these crystals can easily be exfoliated down to monolayer and used to construct heterostructures of different 2D materials connected by vdW force [3]. Metal, semiconductor, and insulator 2D materials have been studied, and various functional electronics and opto-electronics devices have been demonstrated with these materials [4][5][6][7]. Further, these 2D materials could be potentially applied in the field of spintronics [8]; for example, long-distance spin transport has been demonstrated in graphene/h-BN heterostructures [9], and spin polarized tunneling has been demonstrated through graphene [10] and h-BN [11,12]. In these experiments, the source for the spin-polarized electrons is a ferromagnetic metal fabricated by the evaporation technique; thus, the interface between the ferromagnetic and non-magnetic materials involves chemical bonding. On the other hand, the vdW interface does not require any chemical bonding at the junction, in principle. Therefore, layered ferromagnetic 2D materials could possibly be used for constructing vdW heterostructures with spintronic functions. Moreover, the vdW hetrostructure could provide another degree of freedom that has not been possible in the conventional spintronics device; such as controlling the interlayer twist [13,14] In Fig. 1(c), optical micrographs of the exfoliated flake and their vdW junction are shown. The area of vdW junction is 67.8 µm 2 . The quality of the vdW interface is analyzed using cross-sectional transmission electron microscopy (TEM), as shown in Fig. 1(d). The TEM image revealed the layered structure of each Fe 0.25 TaS 2 flake with a stacking period of 0.61 nm; this period is close to the reported value for the bulk material [18]. The vdW contact between the flakes is clearly visible in the TEM image [ Fig. 1(d)].The TEM reveals that vdW junction displays different TEM contrast from the flake; this behavior is attributed to the presence of a native oxide layer existing at the surface of cleaved Fe 0.25 TaS 2 . The presence of Ta 2 O 5 oxide layer in the topmost layer of the exfoliated Fe 0.25 TaS 2 surface i...

Electric-field control of magnetism in a few-layered van der Waals ferromagnetic semiconductor

“…[7][8][9][10][11][12][13][14][15][16][17] For example, the long-standing Mermin-Wagner restriction [18] has been recently lifted in the monolayer limit in CrI 3 , which shows Ising ferromagnetism despite of the zero out-of-plane dimensionality [19,20]. Previous studies on few-layered vdW magnets have also manifested much promising physical phenomena, including the observation of spin-resolved Raman modes, [21,22] the spin waves measured by neutron scattering, [23] potential applications in spinvlaves, [24] as well as the synthesis of new magnetic semiconductors by doping non-magnetic vdW crystals. [25,26] Recent advances in the peculiar tunnelling magneto-resistance in CrI 3 further reveals that atomically thin vdW magnetic materials may serve as potential magnetic sensors.…”

Mechanical and liquid phase exfoliation of cylindrite: a natural van der Waals superlattice with intrinsic magnetic interactions

“…Finally, we also provide a magnetic characterization of bulk and exfoliated cylinders which display magnetic correlations below 20 K. Cylindrite and other intrinsically magnetic natural https://iopscience.iop.org/article/10.1088/2053-1583/ab1a4c heterostructures could therefore be an interesting alternative to expand the exiguous family of the 2D magnetic materials [33][34][35]. Cylindrite presents the additional advantage of being stable in ambient conditions and conducting and therefore of potential interest for magneto-transport [36,37], in contrast with other insulating magnetic 2D materials. Cylindrite belongs to the sulfosalt mineral family and it has an approximate formula Pb3Sn4FeSb2S14.…”

Anomalous Hall effect mechanisms in the quasi-two-dimensional van der Waals ferromagnet Fe0.29TaS2

“…Indeed, to fully understand this feature, future experimental verification of the domain structures for various thickness Fe0.29TaS2 flakes would be essential [33,34]. Nevertheless, the strong thickness dependence of Bc in 2D Fe0.29TaS2 could be useful for designing the giant and tunneling magnetoresistance devices based on its heterostructures [16,[35][36][37][38].…”

“…Figure 1(a) shows the crystalline structure of the layered Fe-intercalated van der Waals ferromagnet FexTaS2, where the Fe atoms are located between the two TaS2 layers. These layers are stacked together via van der Waals interaction with an interlayer distance of ≈ 6 Å. FexTaS2 single crystals are synthesized using the iodine vapor transport method, as described in previous reports [16,[21][22][23][24]. The concentration of Fe (x) in synthesized FexTaS2 single crystals is determined to be 0.29 by energy-dispersive spectroscopy ( Fig.…”