Enhancement of interlayer exchange in an ultrathin two-dimensional magnet

Abstract

Main Text:Following the recent isolation of monolayer CrI3 1 , there has been a surge of new twodimensional van der Waals magnetic materials 2-12 , whose incorporation in van der Waals heterostructures offers a new platform for spintronics 5-8 , proximity magnetism 13 , and quantum spin liquids 14 . A primary question in this burgeoning field is how exfoliating crystals to the few-layer limit influences their magnetism. Studies on CrI3 have shown a different magnetic ground state for ultrathin exfoliated films 1,5,6 but the origin is not yet understood. Here, we use electron tunneling through few-layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in the interlayer exchange compared to bulk crystals. Moreover, temperatureand polarization-dependent Raman spectroscopy reveal that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low temperature stacking order and, we hypothesize, increased interlayer exchange. Our study provides new insight into the connection between stacking order and interlayer interactions in novel two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets, such as RuCl3 14 .A key family of van der Waals magnets is the layered transition metal trihalides, which have been studied for decades as prototypical magnetic insulators 15-17 and as a platform for quasitwo-dimensional magnetism [18][19][20] . In the chromium trihalides, the Cr atoms are arranged in a honeycomb structure, with each Cr atom surrounded by six halide atoms in an octahedral geometry (Fig. 1a). The bulk crystals undergo a crystallographic phase transition from a monoclinic phase (space group C2/m) at room temperature to a rhombohedral phase (space group R3 " ) at low temperatures (below about 240 K for CrCl3 21 ). While the intralayer lattice spacings are largely

Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures

“…[20][21][22] Meanwhile, 2D ferromagnetism has been recently achieved in vdW materials, such as few-layer Cr2Ge2Te3, 23 CrI3, 24 and Fe3GeTe2, 25,26 spurring substantial interests to fabricate ultra-thin magnetic devices and study fundamental properties, such as magnons, spin liquids, and many other quantum states in reduced-dimensional structures. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] All these advances pave the way for exploring the existence of 2D multiferroics and magnetoelectronic couplings.…”

Determining the phase diagram of atomically thin layered antiferromagnet CrCl3

“…Consistently with the above considerations, in trilayers theory predicts the conductance to be constant for H < H 1 , and indeed, the measured magnetoconductance curve is rather flat at low field. A small dip is nevertheless present around H = 0 (whose magnitude is sample 44,45 and bias dependent; see Supplementary Fig. 5) that gives rise to the split peak in dG/dH around H = 0 (see the blue curve in Fig.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…For 2D-CrI 3 and CrBr 3 , optical methods, such as MOKE and RMCD, have been utilized, 67 while tunneling device has been adopted for CrCl 3 . 68 MCD signals of exfoliated monolayer, bilayer and trilayer CrBr 3 have been observed at low temperatures, with magnetic hysteresis showing remanent magnetization. 67 On the other hand, temperature-dependent conductance at zero applied field has been for CrCl 3 tunneling devices, with an marked decrease in the conductance between 14 and 16 K, reflecting an onset of interlayer antiferromagnetic alignment, in agreement with bulk Néel temperature.…”

“…The Curie temperatures of 2D‐CrX 3 obtained by various experimental tools. For 2D‐CrI 3 and CrBr 3 , optical methods, such as MOKE and RMCD, have been utilized, while tunneling device has been adopted for CrCl 3 . MCD signals of exfoliated monolayer, bilayer and trilayer CrBr 3 have been observed at low temperatures, with magnetic hysteresis showing remanent magnetization .…”