Local Magnetic Moments Research Articles

Microscopic origins and stability of ferromagnetism in Co3Sn2S2

Based on the density functional theory, we examine the origin of ferromagnetism in the Weyl semimetal ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ using different types of response theories. We argue that the magnetism of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ has a dual nature and bears certain aspects of both itineracy and localization. On the one hand, the magnetism is soft, where the local magnetic moments strongly depend on temperature and the angles formed by these moments at different Co sites of the kagome lattice, as expected for itinerant magnets. On the other hand, the picture of localized spins still remains adequate for the description of the local stability of the ferromagnetic (FM) order with respect to the transversal spin fluctuations. For the latter purposes, we employ two approaches, which provide quite different pictures for interatomic exchange interactions: the regular magnetic force theorem and a formally exact theory based on the calculation of the inverse response function. The exact theory predicts ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ to be a three-dimensional ferromagnet with the strongest interaction operating between next-nearest neighbors in the adjacent kagome planes. The ligand states are found to play a very important role by additionally stabilizing the FM order. When the local moments decrease, the interplane interactions sharply decrease, first causing the FM order to become quasi-two-dimensional, and then making it unstable with respect to the spin-spiral order propagating perpendicular to the kagome plane. The latter instability is partly contributed by the states at the Fermi surface and may be relevant to the magnetic behavior of ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ near the Curie temperature. Peculiarities of the half-metallic ferromagnetism in ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ are also discussed.

Structural phase transitions and magnetism of Cr doped InN under high pressure

The density functional theory (DFT) calculations within the generalized gradient approximation + U (GGA + U) had been performed to acquire the electronic structure, enthalpy, and magnetic properties of Cr0.5In0.5N under hydrostatic pressure of 0 GPa–20 GPa, the three common structures of InN were used as doped subjects to study related properties of Cr doped InN, including wurtzite (B4), zinc-blende (B3) and rocksalt phase (B1). The enthalpy calculations demonstrated the doped system would occur structural phase transitions at high pressure, and the transition pressures were 7.20 GPa and 9.09 GPa for B4 to B1 and B3 to B1, respectively. Moreover, the total DOS and partial DOS showed a half-metallic character for all doped structures, also showed spin polarization of Cr0.5In0.5N. The total magnetic moment and local magnetic moment were investigated from the ferromagnetic structures of Cr0.5In0.5N, the total magnetic moment of B1 was always 3 μB under normal pressure or high pressure, however, the total magnetic moment of B3 increased with pressure, and it would reach a maximum of 3 μB under high pressure. What's more, we found that the Curie temperature (TC) of B3 decreased slowly with pressure increasing, and the TC was higher than room temperature under the pressure of less than 20 GPa all the time.

Unveiling the role of Y content in glass-forming ability and soft magnetic properties of Co-Y-B metallic glasses by experiment and ab initio molecular dynamics simulations

The effects of Y content on glass-forming ability (GFA) and soft magnetic properties of Co75-xYxB25 (x = 0, 3.5, 5) metallic glasses (MGs) were investigated by experiment and ab initio molecular dynamics (AIMD) simulations, and the relationship between local atomic structures and properties was discussed. The GFA and magnetic softness of Co75B25 alloy are improved by 3.5 at.% Y addition in our experiment. By calculating the local atomic structures (pair distribution function, coordination numbers, chemical short-range order, Voronoi polyhedron, structure factor, and the ratio of voids), dynamic behavior, electronic structure, magnetic moment, and magnetic anisotropy energy (MAE), we have found that the local atomic structures of Co-Y-B MGs are dominated by the B-centered prism units, and Y plays a vital role in the formation of the densely packed structures. In particular, the strongest chemical affinity of B-B, Co-Y, and B-Y pairs in Co71.5Y3.5B25 alloy is the critical factor for enhancing GFA and magnetic softness, which improves the degree of atomic packing in the first shell, the viscosity of supercooling melts, the stability of the local atomic structures, and reduces the MAE of the system. However, the excessive addition of Y (5 at.%) leads to a reduction of the GFA and magnetic softness, which may contribute to the highest fraction of deformed body-centered cubic (bcc) structures and the largest size of the medium-range order (MRO) structure in Co70Y5B25 alloy. This study shows a valuable perspective to understand the correlation between local atomic structures and properties of Co-based MGs, and also provides ideas for designing high-performance soft-magnetic MGs.

No observation of chiral flux current in the topological kagome metal CsV3Sb5

Compounds with kagome lattice usually host many exotic quantum states, including the quantum spin liquid, non-trivial topological Dirac bands and a strongly renormalized flat band, etc. Recently an interesting vanadium based kagome family $A$V$_{3}$Sb$_{5}$ ($A$ = K, Rb, or Cs) was discovered, and these materials exhibit multiple interesting properties, including unconventional saddle-point driving charge density wave (CDW) state, superconductivity, etc. Furthermore, some experiments show anomalous Hall effect which inspires that there might be some chiral flux current states. Here we report scanning tunneling measurements by using spin-polarized tips. Although we have observed clearly the $2a_0\times2a_0$ CDW and $4a_0$ stripe orders, the well-designed experiments with refined spin-polarized tips do not reveal any trace of the chiral flux current phase in CsV$_3$Sb$_5$ within the limits of experimental accuracy. No observation of the local magnetic moment in our experiments may put an upper bound constraint on the magnitude of magnetic moments induced by the possible chiral loop current which has a time-reversal symmetry breaking along $c$-axis in CsV$_{3}$Sb$_{5}$.

Ab initio calculations of electronic properties and charge transfer in Zn-=SUB=-1-x-=/SUB=-Cu-=SUB=-x-=/SUB=-O with wurtzite structure

The results of studying the electronic structure and the influence of the local environment of the copper impurity on the properties and magnetic moment in supercells in Zn1-xCuxO are presented. DFT calculations were carried out in the local electron density (LDA) and generalized gradient approximation (GGA). The band structure of in Zn1-xCuxO was calculated taking into account the correction for spin polarization and the strong electronic interaction. DFT LSDA + U and SGGA + U (U is the Coulomb interaction) calculations made it possible to take into account the contributions of the 3d shells of the Zn and Cu cations to the band spectrum of in Zn1-xCuxO. The introduction of copper into the ZnO lattice leads to a change in the impurity and valence bands of in Zn1-xCuxO. In this case, the bottom of the in Zn1-xCuxO conduction band shifts towards low energies. The total density of electronic states of in Zn1-xCuxO near the Fermi level is mainly determined by the 3d states of Zn and Cu and the 2p state of oxygen. ZnO doped with copper acquires a magnetic moment. The introduction of a vacancy into a supercell in Zn1-xCuxO noticeably changes the local magnetic moment. As the copper concentration in Zn1-xCuxO (x=0, 0.01, and 0.02) increases, the conductivity of the samples in both constant and alternating current increased, and the activation energy of conduction decreased. Keywords: ZnO, copper doping, density functional theory, band calculations, electronic structure, localized magnetic moment, defect formation energies, Zn1-xCuxO, charge transfer, parameters of localized states.

DFT Calculations for Structural, Electronic, and Magnetic Properties of ZnFe2O4 Spinel Oxide: The Role of Exchange-Correlation Functional

In this study, quantum-mechanical calculations in the framework of the Density Functional Theory (DFT) were performed to investigate the role of exchange-correlation functional in describing structural, electronic, and magnetic properties of ZnFe2O4. Herein B3LYP, PBE0, B1WC, and WC1LYP functionals implemented in the CRYSTAL17 code were considered due to the different amounts of the exact Hartree-Fock exchange fraction. In particular, the role of HF fraction on ZnFe2O4 properties was addressed for the first time. Indeed, structural, electronic, and magnetic properties indicate the dependence upon the exchange fraction, where WC1LYP with a 16% exact HF exchange exhibits the best performance compared to the other hybrid functionals. The obtained results reveal an excellent agreement for bandgap, local magnetic moment, long-range magnetic ordering, and unit-cell lattice parameters, overcoming previous theoretical studies based on local/semilocal exchange-correlation treatments. These results confirm the importance of hybrid HF/DFT with controlled HF term contribution to describe the essential features of strongly correlated materials.

Conduction band-edge valley splitting in two-dimensional ferroelectric AgBiP2S6 by magnetic doping: towards electron valley-polarized transport.

Two-dimensional valleytronic systems, using the valley index of carriers to perform logic operations, serves as the basis of the next-generation information technologies. For efficient use of the valley degree of freedom, the major challenge currently is to lift the valley degeneracy to achieve valley splitting. In this work, using first-principles calculations, we propose that valley splitting can be readily achieved in a ferroelectric AgBiP2S6 monolayer by TM doping (TM = V, Cr, Mn, Fe, Co, and Ni), which is highly feasible in experiments. In sharp contrast to most previous reports of valley-related features in the valence band-edge, the pristine AgBiP2S6 monolayer has a direct band-gap located at K/K′ points of the Brillouin zone and harbors strong coupled spin and valley physics around the conduction band-edge, due to inversion symmetry breaking combined with strong spin–orbit coupling. By TM-doping, the local magnetic moment can be introduced into the system, which can destroy the valley degeneration of the conduction band-edge and induce valley splitting. Especially in a V-doped system, accompanied with a large valley splitting (26.8 meV), there is a serious n-type doping in AgBiP2S6. The efficient electron-doping moves the Fermi level just located between the conduction band minimum of the K/K′ valleys, which is suitable for valley-polarized transport. Moreover, the valley-polarized index can be flipped by applying a small magnetic field to rotate the magnetocrystalline direction. The magnitude of valley splitting relies on the strength of orbital hybridization between the TM-d and Bi-p states and can be tuned continually by applying biaxial strain. Under an in-plane electric field, such valley degeneracy breaking would give rise to the long-sought anomalous valley Hall effect, which is crucial to design a valleytronic device.

Ab initio расчет зонной структуры и свойств модификаций соединения Ti-=SUB=-3-=/SUB=-Sb, допированного литием

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2×2×2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a = 5.217 Å) and tetragonal system (D8_m type structure; а = 10.457 Å, с = 5.258 Å). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8_mTi3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti–Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8_m) of Ti3Sb near the Fermi level for s, p, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8_m) increase the magnetic moment (M) as compared to the value of M (M_tot = 0.08 μ_B) of a “pure” Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb–Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb–Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti–Sb–Li system has been established. The isothermal section of the Ti–Sb–Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (<6.25 at. % Li) into the Ti3Sb (Space group Pm3 ̅n; № 223; a = 5.217 Å) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb–Li supercell.

Ab initio calculation of the band structure and properties of modifications of the Ti-=SUB=-3-=/SUB=-Sb compound doped with lithium

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2x2x2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a=5.217 Angstrem) and tetragonal system (D8m type structure; a=10.457 Angstrem, c=5.258 Angstrem). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8m Ti3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti-Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8m) of Ti3Sb near the Fermi level for s-, p-, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8m) increase the magnetic moment (M) as compared to the value of M (M=0.08 μB) of a "pure" Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb-Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb-Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti-Sb-Li system has been established. The isothermal section of the Ti-Sb-Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (≤6.25 at.% Li) into the Ti3Sb (Space group Pm3 n; N 223; a=5.217 Angstrem) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb-Li supercell. Keywords: Ti3Sb intermetallic compounds, A15 cubic modification, D8m tetragonal modification, doping with lithium, Ti3Sb-Li, DFT-LSDA calculations, supercell, electronic and magnetic properties, Ti-Sb-Li phase stability.

Superparamagnetism of potassium-doped tris(diphenacyl) iron

Synthesis and exploration of intriguing physical properties of alkali-metal-doped aromatic hydrocarbons have been the important research topics in the fields of physics, chemistry and materials science. In this work, a powder sample of potassium-doped tris(diphenacyl) iron molecular crystal is prepared by the high-vacuum annealing method. The X-ray diffraction results show that the crystal structure of the synthesized sample is different from that of pristine tris(diphenacyl)iron. The direct current (DC) magnetic susceptibilitiy shows a pronounced hump structure near 8.0 K, which is distinct from the paramagnetism of pristine material in the whole temperature range of 1.8–300 K. The alternating current (AC) magnetic susceptibility shows that the hump has a significant frequency dependence, which can safely rule out the possibility of antiferromagnetism. The combination of the Vogel-Fulcher law, the Néel-Brown model and the critical slowing down model reveals that the hump originates from superparamagnetism with a blocking temperature (<i>T</i><sub>B</sub>) of about 8.0 K. According to the results of Raman spectroscopy, it can be confirmed that the 4s electrons of potassium in the doped material are transferred to the benzene ring of tris(diphenacyl)iron, causing the characteristic Raman modes to be red-shifted and the local magnetic moment to form. Our work is of great significance in exploring alkali-metal-doped aromatic hydrocarbons, and provides a new route for searching organic magnetic materials.

Structural, magnetic and ferroelectric properties of VOBr<sub>2 </sub>monolayer: A first-principles study

On the basis of first-principles calculations, the structure, magnetism and ferroelectricity of VOBr<sub>2</sub> monolayer are studied systematically in the present work. The calculation results indicate that a spontaneous ferroelectric distortion takes place at low temperature, causing the structure of VOBr<sub>2</sub> to transform from a centrosymmetric paraelectric phase to a ferroelectric one. In contrast with its sister compound VOI<sub>2</sub>, the dimerization of V is unstable in VOBr<sub>2</sub> and may quench the local magnetic moment on V ions. Additionally, the easy magnetization axis of VOBr<sub>2</sub> monolayer is in-plane along the <i>a</i>-axis, and the magnetic coupling between adjacent local moments is antiferromagnetic both along the <i>a</i>-axis and along the <i>b</i>-axis. Moreover, the ferroelectric displacement of V ions occurs in the <i>a</i>-axis, along the V—O—V chains direction, resulting in a polarization of about 40 μC/cm<sup>2</sup>. Comparing with the ferro-to-paraelectric reversal pathway, the energy barrier can be effectively reduced for ferroelectric switching on partial or individual V—O—V chains. It is reasonable to believe that the dipole moment flipping on specific chain can be achieved through a moderate external field, thereby providing new direction for designing the low-energy-consumption and high-density ferroelectric memory device.

The Nature of Mn-Mn Coupling in Mn-Ni-Al Alloys

"The occurrence of ferro - and antiferromagnetism in Mn-Ni-Al alloys is governed by the sign of the direct exchange interaction between the Mn magnetic ions. Experimentally has been found that, if the separation between the Mn magnetic ions is greater than the critical value dcr= 2.91 Å, they are ferromagnetic and if the distance is less than the critical value, they are antiferromagnetic. The value of Mn local magnetic moment depends on the number of Al atoms in the first vicinity but the dominant factor is the Mn-Al distance. The nature of Mn-Mn exchange coupling was studied through X-ray diffraction, magnetic and XPS measurements. Keywords: exchange coupling, local magnetic moments, crystallographic structure, electronic structure "

XPS on Mn0.95Dy0.05NiSb Heusler Alloy

"XPS results on Mn0.95Dy0.05NiSb Heusler alloy are presented. The compound is single phase with a C1b type cubic structure. All the experimental results suggest that the rare earth atoms entered in the lattice and they are not forming second phases. An exchange splitting of Mn 3s core-level spectrum of about 4.6 eV was shown, giving a direct evidence of the local magnetic moments on Mn sites. The Ni 3d states are giving the major contribution to the XPS valence band spectra. The Ni 3d satellite peak situated around 6 eV was attributed to the fact that the Ni 3d states in the valence band are not fully occupied. However, the Ni 3d band is almost full in this alloy and the Stoner criterion for the existence of a magnetic moment on Ni sites is no longer fulfilled. Keywords: Heusler alloys, X-ray photoelectron spectroscopy, valence band spectra. "

The effect of Co substitution on the stability and magnetic behavior of FeAg nanoalloys

In this research the structural and magnetic properties of 19-atom Fe-Co-Ag trimetallic nanoalloys have been investigated systematically. In the study, both empirical potentials (EP) and DFT approaches on Fe2ConAg17-n nanoalloys have been performed. For this reason, the global minimum structures and a few low-energy isomers optimized by EP are subjected to DFT reoptimization. It has been found that the double icosahedron structure is the lowest energy configuration for trimetallic Fe2ConAg17-n nanoalloys and fixed two Fe atoms are preferentially located in the inner sites of the nanoalloys. It has also been found that total magnetic moment increases in general and a wide range of magnetic moment values can be obtained by alloying with Co atoms. It is also clear that the local magnetic moments and the local charges of the constituent atoms are well correlated with the composition and the local coordination of the Co atoms.

Orbitally selective Mott phase in electron-doped twisted transition metal-dichalcogenides: A possible realization of the Kondo lattice model

Moir\'e superpotentials in two-dimensional materials allow unprecedented control of the ratio between kinetic and interaction energy. By this they pave the way to study a wide variety of strongly correlated physics under a new light. In particular, the transition-metal dichalcogenides (TMDs) are promising candidate ``quantum simulators'' of the Hubbard model on a triangular lattice. Indeed, Mott and generalized Wigner crystals have been observed in such devices. Here we theoretically propose to extend this model into the multiorbital regime by focusing on electron-doped systems at filling higher than 2. As opposed to hole bands, the electronic bands in TMD materials include two, nearly degenerate species, which can be viewed as two orbitals with different effective mass and binding energy. Using realistic band-structure parameters and a slave-rotor mean-field theory, we find that an orbitally selective Mott (OSM) phase can be stabilized over a wide range of fillings, where one band is locked in a commensurate Mott state, while the other remains itinerant with variable density. This scenario thus realizes the basic ingredients in the Kondo lattice model: a periodic lattice of localized magnetic moments interacting with metallic states. We also discuss possible experimental signatures of the OSM state.

Structural, magnetic, electronic, and phonon properties of NdNiO2 under pressure from first-principles

In this paper, the structural, electronic, magnetic, and phonon properties of NdNiO2 under the pressure range between 0 and 20 ​GPa are studied. The ground state of NdNiO2 is the C-AFM phase within the pressure range of 0–20 ​GPa. Another surprising finding is that no matter what the pressure is, no matter what kind of magnetic structure, the local magnetic moment of Nd is almost 3.0 μB. The results suggest that assuming the spin value of Nd moment is always 3.0 μB, which is a characteristic of an f3 Hund's rule. The electronic structures for the stable C-AFM magnetic configuration of NdNiO2 under the pressure range between 0 and 20 ​GPa show metallic properties. Both the Nd-f bands and Ni-3dxy bands across the Fermi level. The phonon spectra show no imaginary modes under the pressure range between 0 and 20 ​GPa, so NdNiO2 is dynamically stable within the pressure scope between 0 and 20 ​GPa. The vibration frequency of the O atom is nearly higher than that of Ni and Nd atoms, the main reason is that the mass of the O atom is much smaller than that of Ni and Nd atoms.

Observation of novel coexistence of Kondo effect and room temperature magnetism in AlN/Al/AlN trilayer thin film

In this work for the first time, we are reporting the unusual observation of the Kondo effect with the coexistence of room temperature ferromagnetism in AlN/Al/AlN trilayer thin film. The grown film shows resistivity minimum at a temperature of ∼48K, which shifts to the lower temperature on the application of magnetic fields. After considering various possibilities for an upturn in resistivity, we found that the Kondo scattering is responsible for upturn at low temperature. The simultaneous presence of ferromagnetism and Kondo scattering is explained by spatial variation of nitrogen vacancy defects from the film surface to the Al sandwich layer. Furthermore, magneto-transport properties of the film measured at different temperature exhibits both negative and positive components described by localized magnetic moment model for the spin scattering of carriers and two-band model, respectively. This work provides insight into the novel co-existence of ferromagnetism and Kondo effect in crystalline AlN.

Geometric wavefront dislocations of RKKY interaction in graphene

Magnetically doped graphene has great potential for applications in spintronics, in which local magnetic moments are coupled by the Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction. RKKY interaction in graphene has attracted intensive interest. However, previous studies only show the features of the RKKY interaction dictated by energy dispersion, leaving the effect of the geometric nature of electronic structures unexplored. Here, we focus on the short-range oscillation behaviors of RKKY interaction contributed by intervalley scattering. Due to the unique geometric nature of electronic structures, two wavefront dislocations emerge in the RKKY interaction corresponding to winding number 1 of graphene. We further demonstrate the robustness of wavefront dislocations against the doping, trigonal warping, and gap opening of energy bands. This study reveals a unique feature for the RKKY interaction and implies the importance of the geometric nature of electronic structures for magnetism.

Graphdiyne doped with transition metal as ferromagnetic semiconductor

Long-range ferromagnetic ordering in semiconductors has become an attractive research hotspot due to its promising potential in spintronics and information technology. Especially the appearance of carbon-based semiconductors represented by graphdiyne (GDY) makes it easy to realize ferromagnetic semiconductors. Herein, a convenient and effective route has been developed to prepare GDY-based magnetic semiconductors using the modification with transition metal elements including Fe, Co, and Ni, respectively. Among them, lightly doped GDY with Co (Co-GDY) exhibits the most outstanding ferromagnetism with a typical Curie's temperature above room temperature. Meanwhile, the coercive field Hc = 78 Oe at T = 300 K of Co-GDY is the smallest, demonstrating characteristics of easy magnetization. Subsequent spin-polarized DFT calculation results reveal that the robust ferromagnetism of Co-GDY arises from the most significant local magnetic moment. Significantly, a noticeable band gap can still be maintained due to the very light doping level. These results reveal an optimization strategy for selecting doping elements, promoting carbon-based semiconductors application in spin-related fields.

Artificial heavy fermions in a van der Waals heterostructure.

Heavy-fermion systems represent one of the paradigmatic strongly correlated states of matter1-5. They have been used as a platform for investigating exotic behaviour ranging from quantum criticality and non-Fermi liquid behaviour to unconventional topological superconductivity4-12. The heavy-fermion phenomenon arises from the exchange interaction between localized magnetic moments and conduction electrons leading to Kondo lattice physics, and represents one of the long-standing open problems in quantum materials3. In a Kondo lattice, the exchange interaction gives rise to a band with heavy effective mass. This intriguing phenomenology has so far been realized only in compounds containing rare-earth elements with 4f or 5f electrons1,4,13,14. Here we realize a designer van der Waals heterostructure where artificial heavy fermions emerge from the Kondo coupling between a lattice of localized magnetic moments and itinerant electrons in a 1T/1H-TaS2 heterostructure. We study the heterostructure using scanning tunnelling microscopy and spectroscopy and show that depending on the stacking order of the monolayers, we can reveal either the localized magnetic moments and the associated Kondo effect, or the conduction electrons with a heavy-fermion hybridization gap. Our experiments realize an ultimately tunable platform for future experiments probing enhanced many-body correlations, dimensional tuning of quantum criticality and unconventional superconductivity in two-dimensional artificial heavy-fermion systems15-17.