The two-dimensional (2D) magnet, a long-standing missing member in the family of 2D functional materials, is promising for next-generation information technology. The recent experimental discovery of 2D magnetic ordering in CrI3, Cr2Ge2Te6, VSe2, and Fe3GeTe2 has stimulated intense research activities to expand the scope of 2D magnets. This review covers the essential progress on 2D magnets, with an emphasis on the current understanding of the magnetic exchange interaction, the databases of 2D magnets, and the modification strategies for modulation of magnetism. We will address a large number of 2D intrinsic magnetic materials, including binary transition metal halogenides; chalogenides; carbides; nitrides; oxides; borides; silicides; MXene; ternary transition metal compounds CrXTe3, MPX3, Fe-Ge-Te, MBi2Te4, and MXY (M = transition metal; X = O, S, Se, Te, N; Y = Cl, Br, I); f-state magnets; p-state magnets; and organic magnets. Their electronic structure, magnetic moment, Curie temperature, and magnetic anisotropy energy will be presented. According to the specific 2D magnets, the underlying direct, superexchange, double exchange, super-superexchange, extended superexchange, and multi-intermediate double exchange interactions will be described. In addition, we will also highlight the effective strategies to manipulate the interatomic exchange mechanism to improve the Curie temperature of 2D magnets, such as chemical functionalization, isoelectronic substitution, alloying, strain engineering, defect engineering, applying electronic/magnetic field, interlayer coupling, carrier doping, optical controlling, and intercalation. We hope this review will contribute to understanding the magnetic exchange interaction of existing 2D magnets, developing unprecedented 2D magnets with desired properties, and offering new perspectives in this rapidly expanding field.

The recent discovery of two-dimensional (2D) magnetic order in monolayer CrI3 and bilayer Fe3GeTe2 has stimulated intense experimental and theoretical activities to expand the family of 2D magnets. Most 2D magnets reported to date are transition metal compounds with unpaired d electrons. Novel 2D intrinsic magnets with long-range p state coupling are also highly desirable. Here, we propose that nonstoichiometry is a feasible and universal strategy to realize long-range p electron magnetic order in 2D metal-shrouded AXenes (Na2N, K2N, and Rb2N), supported by our first-principles calculations. Taking K2N as a representative, three series of cation-deficient K2N (T, H, and I phases) have been predicted as stable ferromagnetic half-metal/metal with a Curie temperature of 480–1180 K. Their robust ferromagnetism is ascribed to the coexistence of carrier-mediated exchange and N–K–N superexchange interaction. Moreover, mechanical deformation can trigger reversible phase transformation by choosing their 3D layered counterpart as the intermediate phase.

The unique bonding feature of TM2Ps contributes to their high stability, excellent catalytic performance, good ductility, and abundant magnetic properties.

The contributions of spin-phonon coupling (SPC) to spin and thermal transport properties are important in the emerging two-dimensional (2D) magnetic semiconductors and are relevant for the data security and working...

Two-dimensional (2D) ferromagnets with high Curie temperature TC are desirable for spintronics applications. However, they are rarely obtained in experiments mainly due to the challenge of synthesizing high-quality 2D crystals, and their TC values are below room temperature. Using first-principles calculations, we design a family of stable 2D FenGeTe2 (4 ≤ n ≤ 7) ultrathin films with coexisting itinerant and localized magnetism. Among them, 2D Fe3GeTe2 and Fe4GeTe2 are ferromagnetic metals with TC = 138 and 68 K; 2D Fe5GeTe2, Fe6GeTe2, and Fe7GeTe2 are Néel’s P-, R-, and R-type ferrimagnetic metals with TC = 320, 450, and 570 K. A thickness-induced magnetic phase transition originates from competition between itinerant and localized states, and also correlates with Fe3+ and Fe2+ content. A valence/orbital-dependent magnetic exchange model is proposed for these effects. Our results reveal a universal mechanism for magnetic coupling in complex magnetic systems.

As an unconventional bonding pattern different from conventional chemistry, the concept of planar hypercoordinate atom was first proposed in the molecular system, and it has been recently extended to 2D...

The interactive control between electron charge and spin is essential to spintronics. Two-dimensional (2D) ferromagnetic semiconductors (FMSs) are a kind of unique candidate materials that could lead to flexible magnetoelectric and magneto-optic applications. In this Letter, we construct a series of van der Waals heterostructures by 2D magnetic CrXh (X = S/Se, h = Cl/Br/I) monolayers. Based on first-principles calculations, both monolayers and heterostructures have been demonstrated as intrinsic FMSs with large magnetic moments, suitable bandgaps, good carrier mobility, and high Curie temperatures. Taking advantage of the heterojunction effect, one can precisely control the charge transport behavior by forming three types of band alignments. Under an external alternating magnetic field, CrSeBr/CrSeCl and CrSBr/CrSI heterostructures can reversibly reconfigure between type-II and type-I band alignments upon switching of the spin direction. Combining the robust magnetic ordering and distinctive spin-polarized band alignment, our designed CrXh based magnetic heterostructures are ideal candidates for innovative magnetic-field-modulated photoelectric devices for realizing ultrarapid and reversible “write-read” processes.

Two-dimensional (2D) intrinsic multiferroics have long been pursued not only for their potential technological applications but also as model systems for studying emergent quantum phenomena and coupling mechanisms between various order parameters in low-dimensional space. However, the realization of 2D multiferroics is still a challenge. In this paper, we reveal that 2D AgCr2X4 (X = S or Se) crystals, which have been synthesized from the non-van der Waals (non-vdW) AgCrX2 bulk phase, are type I half-metallic/metallic multiferroics in which ferroelectricity and ferromagnetism coexist. The off-centering displacement of the Ag ion introduces out-of-plane polarization, and the magnetism originates from the interactions between Cr atoms. Remarkably, AgCr2Se4 shows topologically nontrivial spin textures, such as Meron pairs and Néel-type skyrmions, under suitable temperatures and magnetic fields. Our findings demonstrate that 2D multiferroics can be achieved from non-vdW materials and in turn open a new avenue for 2D multiferroics.