Exchange Bias in Molecule/Fe₃GeTe₂ van der Waals Heterostructures via Spinterface Effects

Abstract

a Curie temperature close to the room temperature and strong out-of-plane anisotropy. [7][8][9][10] Moreover, the magnetic properties of FGT are tunable, as they can be modified either electrically, applying a gate voltage [11] and a large electrical current, [12] or through magnetic proximity effects. [13][14][15][16] In particular, when interfaced with antiferromagnetic layered materials, FGT displays an increased coercivity and exchange bias, [13][14][15][16] which are the prototypical manifestation of magnetic proximity [17][18][19] and are key elements in spintronic devices. [20] Another attractive approach to tune the properties of a magnetic surface is molecular functionalization. [21,22] The interfaces between magnetic materials and molecules, often named spinterfaces, [21,22] host hybrid states or magnetic interactions which lead to radical changes on the magnetic properties of both the molecular layer [23][24][25][26][27][28][29][30] and the magnetic material. [27][28][29][30][31][32][33] So far, the ferromagnetic layers used for investigating spinterface effects are typically films of 3d metals or oxides with dangling bonds on the surface, which result in nonideal interfaces with molecules. Moreover, until recently, the molecular side of a spinterface has been the main target of research due to its easily tunable electronic properties, [23][24][25][26][27][28][29] whereas the possibility of tailoring the magnetism of ferromagnetic materials has yet to be fully exploited.Layered magnetic materials are excellent candidates for developing a spinterface in view of their tunable magnetism and their single crystalline nature, which offer the possibility to form highly controllable interfaces with molecules [34,35] via the so-called van der Waals epitaxy. [36][37][38][39] Indeed, hybrid heterostructures based on atomically sharp 2D material/molecule interfaces have been widely used to tailor the optoelectronic and transport properties of nonmagnetic layered materials. [40][41][42][43][44][45] However, so far the possibility to tune the properties of a layered magnetic material through the magnetic interactions at a van der Waals spinterface has not yet been experimentally demonstrated.Here, we report on the emergence of spinterface effects between molecular films of Co-phthalocyanine (CoPc) and a few-nm-thick FGT flakes. The molecular layer induces a negative magnetic exchange bias in FGT, indicating that the The exfoliation of layered magnetic materials generates atomically thin flakes characterized by an ultrahigh surface sensitivity, which makes their magnetic properties tunable via external stimuli, such as electrostatic gating and proximity effects. Another powerful approach to engineer magnetic materials is molecular functionalization, generating hybrid interfaces with tailored magnetic interactions, called spinterfaces. However, spinterface effects have not yet been explored on layered magnetic materials. Here, the emergence of spinterface effects is demonstrated at the interface between flakes of the ...

Exchange Bias State at the Crossover to 2D Ferromagnetism

“…Bulk vs Monolayer Limits. EB in 2D materials is detected by various means such as measuring the magneto-optic Kerr effect, 25,26,30 the anomalous Hall effect, 23,24,27,29,31 or the reflectance magnetic circular dichroism. 24,26 The large area of the samples produced by MBE allows for direct magnetization measurements of the samples by a SQUID magnetometer.…”

“…EB in 2D materials is detected by various means such as measuring the magneto-optic Kerr effect, ,, the anomalous Hall effect, ,,,, or the reflectance magnetic circular dichroism. , The large area of the samples produced by MBE allows for direct magnetization measurements of the samples by a SQUID magnetometer. These measurements are accompanied by a study of electron transport in GdSi 2 films (see Methods for technical details).…”

“…The research is dominated by heterostructures of FGT (Fe n GeTe 2 , n = 3, 5), including FGT/CrCl 3 , FGT/CrOCl, FGT/FePS 3 , FGT/MnPS 3 , and FGT/MnPSe 3 . The number of possibilities is immense: to produce EB, FGT has been coupled with molecular layers, a non van der Waals AFM material, sandwiched between two AFM materials. , EB can also be induced by chemical modification such as surface oxidation or protonation of FGT nanoflakes; proton intercalation provides gate-tunable EB in FGT/FePS 3 . The physical origins of the observed EB effects are under debate. , However, the potential of 2D materials in applications is evident.…”

“…The physical origins of the observed EB effects are under debate. , However, the potential of 2D materials in applications is evident. In particular, they give impetus to search for large EB fieldssubstantial EB effects, reaching almost 1 kOe, have been detected in heterostructures of FGT. − …”

2D Magnetic Semiconductor Fe3GeTe2 with Few and Single Layers with a Greatly Enhanced Intrinsic Exchange Bias by Liquid-Phase Exfoliation

“…Research on the properties of 2D FGT is still in the preliminary stage, and further studies are required. For example, the exchange bias (EB) originating from the unidirectional pinning on the ferromagnetic/antiferromagnetic (FM/AFM) interface − in vdW magnetic heterojunctions has huge potential applications in magnetic random-access memory, magnetic tunnel junctions, etc. By carefully designing the vdW stacking structure, Hu et al obtained an EB of 253 Oe at 10 K and observed an antisymmetric magnetoresistance in the FGT/MnPS 3 heterostructure.…”