Showing papers on "Magnetic anisotropy published in 2021"

Recent progress on 2D magnets: Fundamental mechanism, structural design and modification

Abstract: 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.

Anomalous thickness dependence of Curie temperature in air-stable two-dimensional ferromagnetic 1T-CrTe2 grown by chemical vapor deposition

Abstract: The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe2 ultrathin crystals with controlled thickness Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition With reducing the thickness of 1T-CrTe2 from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane Monotonic increase of Curie temperature with the thickness decreasing from ~1300 to ~76 nm is observed Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties

Direct observation of two-dimensional magnons in atomically thin CrI3

Abstract: Magnons are collective spin excitations in crystals with long-range magnetic order. The emergent van der Waals magnets1–3 provide a highly tunable platform to explore magnetic excitations in the two-dimensional limit with intriguing properties, manifesting from their honeycomb lattice structure and switchable magnetic configurations. Here, we report the direct observation of two-dimensional magnons through magneto-Raman spectroscopy with optical selection rules determined by the interplay between crystal symmetry, layer number and magnetic states in atomically thin CrI3. In monolayers, we observe an acoustic magnon mode at ~0.3 meV. It has strict cross-circularly polarized selection rules locked to the magnetization direction that originates from the conservation of angular momentum of photons and magnons dictated by three-fold rotational symmetry4. Additionally, we reveal optical magnon modes at ~17 meV. This mode is Raman silent in monolayers, but optically active in bilayers and bulk due to a relaxation of the parity criterion resulting from the layer index. In the layered antiferromagnetic states, we directly resolve two degenerate optical magnon modes with opposite angular momentum and conjugate optical selection rules. From these measurements, we quantitatively extract the spin-wave gap, magnetic anisotropy and intralayer and interlayer exchange constants, and establish two-dimensional magnets as a new platform for exploring magnon physics. Magnons are collective excitations that dictate many of a magnet’s low-temperature properties. By means of Raman scattering, the magnon spectra of CrI3 are measured in the monolayer limit.

Square skyrmion crystal in centrosymmetric itinerant magnets

Abstract: We theoretically investigate the origin of the square-type skyrmion crystal in centrosymmetric itinerant magnets, motivated by the recent experimental findings in ${\mathrm{GdRu}}_{2}{\mathrm{Si}}_{2}$ [N. D. Khanh et al., Nat. Nanotech. 15, 444 (2020)]. By simulated annealing for an effective spin model derived from the Kondo lattice model on a square lattice, we find that a square skyrmion crystal composed of a superposition of two spin helices is stabilized in a magnetic field by synergy between the positive biquadratic, bond-dependent anisotropic, and easy-axis anisotropic interactions. This is in stark contrast to triangular skyrmion crystals, which are stabilized by only one of the three, suggesting that the square skyrmion crystal is characteristic of itinerant magnets with magnetic anisotropy. We also show that a variety of noncollinear and noncoplanar spin textures appear, depending on the model parameters as well as the applied magnetic field. The present systematic study will be useful not only for identifying the key ingredients in ${\mathrm{GdRu}}_{2}{\mathrm{Si}}_{2}$ but also for exploring further skyrmion-hosting materials in centrosymmetric itinerant magnets.

A complete ab initio view of Orbach and Raman spin-lattice relaxation in a Dysprosium coordination compound.

Abstract: The unique electronic and magnetic properties of Lanthanides molecular complexes place them at the forefront of the race towards high-temperature single-ion magnets and magnetic quantum bits. The design of compounds of this class has so far been almost exclusively driven by static crystal field considerations, with emphasis on increasing the magnetic anisotropy barrier. This guideline has now reached its maximum potential and new progress can only come from a deeper understanding of spin-phonon relaxation mechanisms. In this work we compute relaxation times fully ab initio and unveil the nature of all spin-phonon relaxation mechanisms, namely Orbach and Raman pathways, in a prototypical Dy single-ion magnet. Computational predictions are in agreement with the experimental determination of spin relaxation time and crystal field anisotropy, and show that Raman relaxation, dominating at low temperature, is triggered by low-energy phonons and little affected by further engineering of crystal field axiality. A comprehensive analysis of spin-phonon coupling mechanism reveals that molecular vibrations beyond the ion's first coordination shell can also assume a prominent role in spin relaxation through an electrostatic polarization effect. Therefore, this work shows the way forward in the field by delivering a novel and complete set of chemically-sound design rules tackling every aspect of spin relaxation at any temperature

Chiral Symmetry Breaking for Deterministic Switching of Perpendicular Magnetization by Spin-Orbit Torque.

Abstract: Symmetry breaking is a characteristic to determine which branch of a bifurcation system follows upon crossing a critical point. Specifically, in spin-orbit torque (SOT) devices, a fundamental question arises: how can the symmetry of the perpendicular magnetic moment be broken by the in-plane spin polarization? Here, we show that the chiral symmetry breaking by the antisymmetric Dzyaloshinskii-Moriya interaction (DMI) can induce the deterministic SOT switching of the perpendicular magnetization. By introducing a gradient of saturation magnetization or magnetic anisotropy, the dynamic noncollinear spin textures are formed under the current-driven SOT, and thus, the chiral symmetry of these dynamic spin textures is broken by the DMI, resulting in the deterministic magnetization switching. We introduce a strategy to induce an out-of-plane (z) gradient of magnetic properties as a practical solution for the wafer-scale manufacture of SOT devices.

Room Temperature Ferromagnetism of Monolayer Chromium Telluride with Perpendicular Magnetic Anisotropy.

Abstract: The realization of long-range magnetic ordering in 2D systems can potentially revolutionize next-generation information technology. Here, the successful fabrication of crystalline Cr3 Te4 monolayers with room temperature (RT) ferromagnetism is reported. Using molecular beam epitaxy, the growth of 2D Cr3 Te4 films with monolayer thickness is demonstrated at low substrate temperatures (≈100 °C), compatible with Si complementary metal oxide semiconductor technology. X-ray magnetic circular dichroism measurements reveal a Curie temperature (Tc ) of v344 K for the Cr3 Te4 monolayer with an out-of-plane magnetic easy axis, which decreases to v240 K for the thicker film (≈7 nm) with an in-plane easy axis. The enhancement of ferromagnetic coupling and the magnetic anisotropy transition is ascribed to interfacial effects, in particular the orbital overlap at the monolayer Cr3 Te4 /graphite interface, supported by density-functional theory calculations. This work sheds light on the low-temperature scalable growth of 2D nonlayered materials with RT ferromagnetism for new magnetic and spintronic devices.

Opening Magnetic Hysteresis by Axial Ferromagnetic Coupling: From Mono-Decker to Double-Decker Metallacrown

Abstract: Combining Ising-type magnetic anisotropy with collinear magnetic interactions in single-molecule magnets (SMMs) is a significant synthetic challenge. Herein we report a Dy[15-MCCu -5] (1-Dy) SMM, where a DyIII ion is held in a central pseudo-D5h pocket of a rigid and planar Cu5 metallacrown (MC). Linking two Dy[15-MCCu -5] units with a single hydroxide bridge yields the double-decker {Dy[15-MCCu -5]}2 (2-Dy) SMM where the anisotropy axes of the two DyIII ions are nearly collinear, resulting in magnetic relaxation times for 2-Dy that are approximately 200 000 times slower at 2 K than for 1-Dy in zero external field. Whereas 1-Dy and the YIII -diluted Dy@2-Y analogue do not show remanence in magnetic hysteresis experiments, the hysteresis data for 2-Dy remain open up to 6 K without a sudden drop at zero field. In conjunction with theoretical calculations, these results demonstrate that the axial ferromagnetic Dy-Dy coupling suppresses fast quantum tunneling of magnetization (QTM). The relaxation profiles of both complexes curiously exhibit three distinct exponential regimes, and hold the largest effective energy barriers for any reported d-f SMMs up to 625 cm-1 .

Noncoplanar multiple- Q spin textures by itinerant frustration: Effects of single-ion anisotropy and bond-dependent anisotropy

Abstract: We theoretically investigate multiple-$Q$ spin textures, which are composed of superpositions of spin density waves with different wave numbers, for an effective spin model of centrosymmetric itinerant magnets. Our focus is on the interplay between biquadratic interactions arising from the spin-charge coupling and magnetic anisotropy caused by the spin-orbit coupling. Taking into account two types of the magnetic anisotropy, single-ion anisotropy and bond-dependent anisotropy, we elucidate magnetic phase diagrams for an archetypal triangular-lattice system in the absence and presence of an external magnetic field. In the case of the single-ion anisotropy, we find a plethora of multiple-$Q$ instabilities depending on the strength and the sign of the anisotropy (easy plane or easy axis), including a skyrmion crystal with topological number of two. In an external magnetic field, we find that a skyrmion crystal with topological number of one is stabilized by the in-plane (out-of-plane) magnetic field under the easy-plane (easy-axis) anisotropy. We also examine the stability of the field-induced skyrmion crystal by rotating the field direction. As a biproduct, we show that a triple-$Q$ state with nonzero chirality appears in the presence of the biquadratic interaction and the easy-axis anisotropy. Meanwhile, we find that the bond-dependent anisotropy also stabilizes both types of skyrmion crystals. We show that, however, for the skyrmion crystal with topological number of one, Bloch- and Neel-type skyrmion crystals are selectively realized depending on the sign of the bond-dependent anisotropy. Moreover, we find yet another multiple-$Q$ states, including two types of meron crystals with the skyrmion numbers of one and two. The systematic investigation will provide a reference to complex magnetic textures in centrosymmetric magnetic metals.

Properties and dynamics of meron topological spin textures in the two-dimensional magnet CrCl3

Abstract: Merons are nontrivial topological spin textures highly relevant for many phenomena in solid state physics. Despite their importance, direct observation of such vortex quasiparticles is scarce and has been limited to a few complex materials. Here, we show the emergence of merons and antimerons in recently discovered two-dimensional (2D) CrCl3 at zero magnetic field. We show their entire evolution from pair creation, their diffusion over metastable domain walls, and collision leading to large magnetic monodomains. Both quasiparticles are stabilized spontaneously during cooling at regions where in-plane magnetic frustration takes place. Their dynamics is determined by the interplay between the strong in-plane dipolar interactions and the weak out-of-plane magnetic anisotropy stabilising a vortex core within a radius of 8-10 nm. Our results push the boundary to what is currently known about non-trivial spin structures in 2D magnets and open exciting opportunities to control magnetic domains via topological quasiparticles.

Controlling the anisotropy of a van der Waals antiferromagnet with light

Abstract: Van der Waals magnets provide an ideal playground to explore the fundamentals of low-dimensional magnetism and open opportunities for ultrathin spin-processing devices. The Mermin-Wagner theorem dictates that as in reduced dimensions isotropic spin interactions cannot retain long-range correlations, the long-range spin order is stabilized by magnetic anisotropy. Here, using ultrashort pulses of light, we control magnetic anisotropy in the two-dimensional van der Waals antiferromagnet NiPS3. Tuning the photon energy in resonance with an orbital transition between crystal field split levels of the nickel ions, we demonstrate the selective activation of a subterahertz magnon mode with markedly two-dimensional behavior. The pump polarization control of the magnon amplitude confirms that the activation is governed by the photoinduced magnetic anisotropy axis emerging in response to photoexcitation of ground state electrons to states with a lower orbital symmetry. Our results establish pumping of orbital resonances as a promising route for manipulating magnetic order in low-dimensional (anti)ferromagnets.

Correlation-driven topological and valley states in monolayer VSi 2 P 4

Abstract: Electronic correlations could have significant impact on the material properties. They are typically pronounced for localized orbitals and enhanced in low-dimensional systems, so two-dimensional (2D) transition metal compounds could be a good platform to study their effects. Recently, a new class of 2D transition metal compounds, the ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$-family materials, has been discovered, and some of them exhibit intrinsic magnetism. Here, taking monolayer ${\mathrm{VSi}}_{2}{\mathrm{P}}_{4}$ as an example from the family, we investigate the impact of correlation effects on its physical properties, based on the first-principles calculations with the $\mathrm{DFT}+U$ approach. We find that different correlation strengths can drive the system into a variety of interesting ground states, with rich magnetic, topological, and valley features. With increasing correlation strength, while the system favors a ferromagnetic semiconductor state for most cases, the magnetic anisotropy and the band gap type undergo multiple transitions, and in the process, the band edges can form single, two, or three valleys for electrons or holes. Remarkably, there is a quantum anomalous Hall (QAH) insulator phase, which has a unit Chern number and has its chiral edge states polarized in one of the valleys. The boundary of the QAH phase corresponds to the half-valley semimetal state with fully valley polarized bulk carriers. We further show that for phases with the out-of-plane magnetic anisotropy, the interplay between spin-orbit coupling and orbital character of valleys enables an intrinsic valley polarization for electrons but not for holes. This electron valley polarization can be switched by reversing the magnetization direction, providing a new route of magnetic control of valleytronics. Our result sheds light on the possible role of correlation effects in the 2D transition metal compounds, and it will open new perspectives for spintronic, valleytronic, and topological nanoelectronic applications based on these materials.

Skyrmion crystals in centrosymmetric itinerant magnets without horizontal mirror plane.

Abstract: We theoretically investigate a new stabilization mechanism of a skyrmion crystal (SkX) in centrosymmetric itinerant magnets with magnetic anisotropy. By considering a trigonal crystal system without the horizontal mirror plane, we derive an effective spin model with an anisotropic Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction for a multi-band periodic Anderson model. We find that the anisotropic RKKY interaction gives rise to two distinct SkXs with different skyrmion numbers of one and two depending on a magnetic field. We also clarify that a phase arising from the multiple-Q spin density waves becomes a control parameter for a field-induced topological phase transition between the SkXs. The mechanism will be useful not only for understanding the SkXs, such as that in Gd $$_2$$ PdSi $$_3$$ , but also for exploring further skyrmion-hosting materials in trigonal itinerant magnets.

Prediction of the two-dimensional Janus ferrovalley material LaBrI

Abstract: Two-dimensional (2D) ferrovalley materials, displaying coexistence of spontaneous spin and valley polarizations, have recently attracted significant attention due to their potential for applications in the fields of spintronics and valleytronics. However, unfortunately, to date only a few 2D ferrovalley materials exist. Here, first-principles calculations predict a 2D Janus ferrovalley material lanthanum bromiodide (LaBrI). It is found that LaBrI is a stable ferromagnetic electride, whose magnetic moment originates mainly from the interstitial anionic electrons. The magnetic transition temperature of LaBrI monolayers is estimated to be far beyond room temperature, and a sizable magnetic anisotropy with easy in-plane magnetization is also present. Most importantly, LaBrI monolayers exhibit a large valley polarization due to the concurrent broken space- and time-reversal symmetries, with the calculated valley polarization reaching up to 59 meV. This value is comparable to that of the ferrovalley materials reported to date. Intriguingly, the inequivalent Berry curvature at the two valleys takes opposite values, giving rise to an anomalous valley Hall effect, where a valley current with an accompanying net charge Hall current may be induced.

Magnetic Anisotropy Trends along a Full 4f-Series: The fn+7 Effect.

Abstract: The combined experimental and computational study of the 13 magnetic complexes belonging to the Na[LnDOTA(H2O)] (H4DOTA = tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid and Ln = Ce-Yb) family allowed us to identify a new trend: the orientation of the magnetic anisotropy tensors of derivatives differing by seven f electrons practically coincide. We name this trend the fn+7 effect. Experiments and theory fully agree on the match between the magnetic reference frames (e.g., the easy, intermediate, and hard direction). The shape of the magnetic anisotropy of some couples of ions differing by seven f electrons might seem instead different at first look, but our analysis explains a hidden similarity. We thus pave the way toward a reliable predictivity of the magnetic anisotropy of lanthanide complexes with a consequent reduced need of computational and synthetical efforts. We also offer a way to gain information on ions with a relatively small total angular momentum (i.e., Sm3+ and Eu3+) and on the radioactive Pm3+, which are difficult to investigate experimentally.

Manipulating Ferromagnetism in Few-Layered Cr 2 Ge 2 Te 6 .

Abstract: The discovery of magnetism in 2D materials offers new opportunities for exploring novel quantum states and developing spintronic devices. In this work, using field-effect transistors with solid ion conductors as the gate dielectric (SIC-FETs), we have observed a significant enhancement of ferromagnetism associated with magnetic easy-axis switching in few-layered Cr2 Ge2 Te6 . The easy axis of the magnetization, inferred from the anisotropic magnetoresistance, can be uniformly tuned from the out-of-plane direction to an in-plane direction by electric field in the few-layered Cr2 Ge2 Te6 . Additionally, the Curie temperature, obtained from both the Hall resistance and magnetoresistance measurements, increases from 65 to 180 K in the few-layered sample by electric gating. Moreover, the surface of the sample is fully exposed in the SIC-FET device configuration, making further heterostructure-engineering possible. This work offers an excellent platform for realizing electrically controlled quantum phenomena in a single device.

Magnetic anisotropy in spin-3/2 with heavy ligand in honeycomb Mott insulators: Application to CrI 3

Abstract: The authors derive a microscopic spin model for transition metals with ${d}^{3}$surrounded by heavy ligands in honeycomb Mott insulators and apply it to ferromagnetic CrI${}_{3}$.

Polymer-buried van der Waals magnets for promising wearable room-temperature spintronics.

Abstract: The demand for high-performance spintronic devices has boosted intense research on the manipulation of magnetism in van der Waals (vdW) magnets. Despite great efforts, robust ferromagnetic transitions above room temperature still face significant hurdles. Strain engineering can reversibly regulate magnetic exchange, but the degree of regulation is still impractical for most magnetic applications. Hereby we employ a large-strain transferrer to produce tunable strains of up to 4.7%, which induces authentic room-temperature ferromagnetism in large-area Fe3GeTe2 nanoflakes with 20-fold improvement in magnetization. The record increment of the Curie temperature (TC) of well above 400 K originates from the strain-enhanced magnetic anisotropy and excellent magnetoelastic coupling. The correlation between the emerging ferromagnetism and Raman spectral evolution is also established, which complements well the TC phase diagram in a large-strain region. In addition, an unusual exchange bias effect with a vertical magnetization shift is tracked for the first time upon bending, which reveals the hidden competition between antiferromagnetic and ferromagnetic coupling. The reversible strain manipulation of single-domain ferromagnetic order in a single nanoflake further opens up a route to develop low-power wearable spintronic devices. The findings here provide vast opportunities to exploit the possibility of practical applications of more vdW magnets.

Triaxial magnetic anisotropy in the two-dimensional ferromagnetic semiconductor CrSBr

Abstract: Two-dimensional (2D) ferromagnets have recently drawn extensive attention, and here we study the electronic structure and magnetic properties of the bulk and monolayer of CrSBr, using first-principles calculations and Monte Carlo simulations. Our results show that bulk CrSBr is a magnetic semiconductor and has the easy magnetization b-axis, hard c-axis, and intermediate a-axis. Thus, the experimental triaxial magnetic anisotropy (MA) is well reproduced here, and it is identified to be the joint effects of spin-orbit coupling (SOC) and magnetic dipole-dipole interaction. We find that bulk CrSBr has a strong ferromagnetic (FM) intralayer coupling but a marginal interlayer one. We also study CrSBr monolayer in detail and find that the intralayer FM exchange persists and the shape anisotropy has a more pronounced contribution to the MA. Using the parameters of the FM exchange and the triaxial MA, our Monte Carlo simulations show that CrSBr monolayer has Curie temperature Tc = 175 K. Moreover, we find that a uniaxial tensile (compressive) strain along the a (b) axis would further increase the Tc.

Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice.

Abstract: Kagome lattice, made of corner-sharing triangles, provides an excellent platform for hosting exotic topological quantum states. Here we systematically studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic structure with different easy axis at low temperature. The low-temperature magnetoresistance (MR) is positive and has no tendency to saturate below 7 T, while the MR gradually declines and becomes negative with the increasing temperature. A large intrinsic anomalous Hall conductivity about 250 {\Omega}-1cm-1, 40 {\Omega}-1cm-1, 95 {\Omega}-1cm-1 is observed for TbMn6Sn6, DyMn6Sn6, HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an excellent platform to discover other intimately related topological or quantum phenomena and also tune the electronic and magnetic properties in future studies.

Magnetic Properties of NbSi2N4, VSi2N4, and VSi2P4 Monolayers

Abstract: The recent demonstration of MoSi2N4 and its exceptional stability to air, water, acid, and heat has generated intense interest in this new family of two-dimensional (2D) materials. Among these materials, NbSi2N4, VSi2N4, and VSi2P4 are ferromagnetic with in-plane magnetization. Within the plane, there is no energy preference to the angle of the magnetic moments. The calculated Curie temperature of monolayer VSi2N4 is room temperature. The magnetic anisotropy energies (MAEs) are small. The moments remain in-plane for uniaxial strains of up to +/-4%. Band flling near experimentally accessible limits will cause VSi2N4 to switch from in-plane to perpendicular magnetic anisotropy and NbSi2N4 to become nonmagnetic.

Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator Mn 3 Si 2 Te 6

Abstract: Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of magnitude with an applied magnetic field above 9 Tesla, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard axis and is surprisingly absent when the magnetic field is applied along the magnetic easy axis where magnetization is fully saturated. The anisotropy field separating the easy and hard axes is 13 Tesla, unexpected for the Mn ions with nominally negligible orbital momentum and spin-orbit interactions. Double exchange and Jahn-Teller distortions that drive the hole-doped manganites do not exist in Mn3Si2Te6. The phenomena fit no existing models, suggesting a unique, intriguing type of electrical transport.

Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice

Abstract: Kagome lattice, made of corner-sharing triangles, provides an excellent platform for hosting exotic topological quantum states. Here, we systematically studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic structure with different easy axis at low temperature. The low-temperature magnetoresistance (MR) is positive and has no tendency to saturate below 7 T, while the MR gradually declines and becomes negative with the increasing temperature. A large intrinsic anomalous Hall conductivity about 250, 40, and 95 Ω−1 cm−1 is observed for TbMn6Sn6, DyMn6Sn6, and HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an excellent platform to discover other intimately related topological or quantum phenomena and also tune the electronic and magnetic properties in future studies.

Magnetic properties of NbSi2N4, VSi2N4, and VSi2P4 monolayers

Abstract: The recent demonstration of MoSi2N4 and its exceptional stability to air, water, acid, and heat has generated intense interest in this family of two-dimensional materials. Among these materials, monolayers of NbSi2N4, VSi2N4, and VSi2P4 are semiconducting, easy-plane ferromagnets with negligible in-plane magnetic anisotropy. They, thus, satisfy a necessary condition for exhibiting a dissipationless spin superfluid mode. The Curie temperatures of monolayer VSi2P4 and VSi2N4 are determined to be above room temperature based on Monte Carlo and density functional theory calculations. The magnetic moments of VSi2N4 can be switched from in-plane to out-of-plane by applying tensile biaxial strain or electron doping.