Giant Uniaxial Magnetocrystalline Anisotropy in SmCrGe 3
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Xu, Mingyu↗
Engineering topics
Lee, Yongbin
Publications and source records attributed to Lee, Yongbin.
CSD 2374310: Experimental Crystal Structure Determination
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Cell Parameters↗
Probing the van Hove singularity of the kagome metal YV 6 Sn 6 through quantum oscillations
Kagome metals with the Fermi energy tuned near the van Hove singularities (vHss) have shown to host exotic phases including unconventional superconductivity and a chiral flux phase arising from a charge density wave. However, most quantum oscillations studies of the electronic structure of kagome metals focus on compounds which electronically or magnetically order, obscuring the unperturbed vHs. Here we present quantum oscillation measurements of YV 6 Sn 6 which contains a pristine kagome lattice free from long-range order. We discovered quantum oscillations corresponding to a large orbit (≈70% of the Brillouin Zone area) with the heaviest mass ever observed in vanadium-based kagome metals (≈3.3m e ), consistent with a Fermi pocket whose Fermi level is near the vHs. Comparing with first-principle calculations suggests that the effective mass of this pocket is highly sensitive to the position of Fermi level. Finally, our study establishes the enhanced density of states associated with a vHs in a kagome metal, allowing further insight into a potential driving mechanism for the unconventional electronic orderings in this class of materials.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Coexistence of ferromagnetism and antiferromagnetic dimers in topological insulators
The addition of magnetic impurities in topological insulators (TIs) can drive ferromagnetic order that leads to quantum anomalous Hall transport well below the Curie temperature. The fragility of the quantized regime has been ascribed to the random nature of the magnetic moment distribution. Here, we refine this hypothesis by using inelastic neutron scattering and density-functional theory calculations to show that two antagonistic components define the magnetism in Mn-substituted SnTe, thereby limiting the effectiveness of dilute magnetic TIs. One component is strongly bound antiferromagnetic dimers that compete with ferromagnetic order. In conclusion, the other component consists of undimerized moments where ferromagnetic order develops via long-range interactions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Dual nature of magnetism driven by momentum dependent f-d Kondo hybridization
The intricate nature of magnetism in uranium-based Kondo lattices is a consequence of correlations between U-5 f and conduction electrons. Previously, the source of magnetism has been ascribed to either Mott physics or Ruderman-Kittel-Kasuya-Yosida interaction, both of which are not fully applicable to uranium-based Kondo lattices. Using linearized quasiparticle self-consistent GW plus dynamical mean-field theory, we demonstrate a crossover from incoherent to coherent f - d Kondo cloud in the paramagnetic phase of UTe 2 , USbTe and USbSe. As the transition occurs, we observe an augmented f - d coherence and Pauli-like magnetic susceptibility, with a substantial frozen magnetic moment of U-5 f persisting. We show that momentum dependent f - d hybridization is responsible for the magnetic moments arising from the renormalized f electrons’ van Hove singularity. Our findings provide a perspective to explain the dual nature of magnetism and the long-range magnetic ordering induced by pressure in UTe 2 .
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Nanoscale visualization and spectral fingerprints of the charge order in ScV 6 Sn 6 distinct from other kagome metals
Charge density waves (CDWs) in kagome metals have been tied to many exotic phenomena. Here, using spectroscopic-imaging scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we study the charge order in kagome metal ScV 6 Sn 6 . The similarity of electronic band structures of ScV 6 Sn 6 and TbV 6 Sn6 (where charge ordering is absent) suggests that charge ordering in ScV 6 Sn 6 is unlikely to be primarily driven by Fermi surface nesting of the Van Hove singularities. In contrast to the CDW state of cousin kagome metals, we find no evidence supporting rotation symmetry breaking. Differential conductance dI/dV spectra show a partial gap Δ 1 CO ≈ 20 meV at the Fermi level. Interestingly, dI/dV maps reveal that charge modulations exhibit an abrupt phase shift as a function of energy at energy much higher than Δ 1 CO , which we attribute to another spectral gap. Our experiments reveal a distinctive nature of the charge order in ScV 6 Sn 6 with fundamental differences compared to other kagome metals.
36 MATERIALS SCIENCE↗
Inducing Ferrimagnetic Exchange in 1D-FeSe 2 Chains Using Heteroleptic Amine Complexes: [Fe(en)(tren)][FeSe 2 ] 2
[Fe(en)(tren)][FeSe 2 ] 2 (en = ethylenediamine, C 2 H 8 N 2 , tren = tris(2-aminoethyl)amine, C 6 H 18 N 4 ) has been synthesized by a mixed-ligand solvothermal method. Its crystal structure contains heteroleptic [Fe(en)(tren)] 2+ complexes with distorted octahedral coordination, incorporated between 1D-FeSe 2 chains composed of edge–sharing FeSe 4 tetrahedra. The twisted octahedral coordination environment of the Fe–amine complex leads to partial dimerization of Fe–Fe distances in the FeSe 2 chains so that the FeSe 4 polyhedra deviate strongly from the regular tetrahedral geometry. 57 Fe Mössbauer spectroscopy reveals oxidation states of +3 for the Fe chain atoms and +2 for the Fe complex atoms. The close proximity of Fe atoms in the chains promotes ferromagnetic nearest neighbor interactions, as indicated by a positive Weiss constant, θ = +53.8(6) K, derived from the Curie–Weiss fitting. Magnetometry and heat capacity reveal two consecutive magnetic transitions below 10 K. DFT calculations suggest that the ordering observed at 4 K is due to antiferromagnetic intrachain interactions in the 1D-FeSe 2 chains. The combination of two different ligands creates an asymmetric coordination environment that induces changes in the structure of the Fe–Se fragments. Finally, this synthetic strategy opens new ways to explore the effects of ligand field strength on the structure of both Fe-amine complexes and surrounding Fe–Se chains.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Pseudogap behavior in charge density wave kagome material ScV 6 Sn 6 revealed by magnetotransport measurements
Over the last few years, significant attention has been devoted to studying the kagome materials A V 3 Sb 5 (A = K, Rb, Cs) due to their unconventional superconductivity and charge density wave (CDW) ordering. Recently $ScV_{6}Sn_{6}$ was found to host a CDW below ≈ 90 K, and, like A V 3 Sb 5 , it contains a kagome lattice comprised only of V ions. Here we present a comprehensive magnetotransport study on $ScV_{6}Sn_{6}$. We discovered several anomalous transport phenomena above the CDW ordering temperature, including insulating behavior in interlayer resistivity, a strongly temperature-dependent Hall coefficient, and a violation of Kohler’s rule. All these anomalies can be consistently explained by a progressive decrease in carrier densities with decreasing temperature, suggesting the formation of a pseudogap. Our findings suggest that high-temperature CDW fluctuations play a significant role in determining the normal state electronic properties of $ScV_{6}Sn_{6}$.
36 MATERIALS SCIENCE↗
Microscopic characterization of the magnetic properties of the itinerant antiferromagnet La 2 Ni 7 by La 139 NMR/NQR measurements
In this study, 139 La nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed to investigate the magnetic properties of the itinerant magnet La 2 Ni 7 , which shows a series of antiferromagnetic (AFM) phase transitions at T N1 = 61 K, T N2 = 56 K, and T N3 = 42 K under zero magnetic field. Two distinct La NMR signals were observed due to the two crystallographically inequivalent La sites in La 2 Ni 7 (La1 and La2 in the La 2 Ni 4 and the LaNi 5 subunits of the La 2 Ni 7 unit cell, respectively). From the 139 La NQR spectrum in the AFM state below T N3 , the AFM state was revealed to be a commensurate state where Ni-ordered moments align along the crystalline c axis. Owing to the two different La sites, we were able to estimate the average values of the Ni-ordered moments (0.09 – 0.10 μB / Ni and 0.17 μB / Ni around La1 and La2, respectively) from 139 La NMR spectrum measurements in the AFM state below T N3 , suggesting a nonuniform distribution of the Ni-ordered moments in the AFM state. In contrast, a more uniform distribution of the Ni-ordered moments in the saturated paramagnetic state induced by the application of high magnetic fields is observed. The temperature dependence of the sublattice magnetization measured by the internal magnetic induction at the La2 site in the AFM state was reproduced by a local-moment model better than the self-consistent renormalization (SCR) theory for weak itinerant antiferromagnets. Given the small Ni-ordered moments in the magnetically ordered state, our results suggest that La 2 Ni 7 has characteristics of both itinerant nature and localized nature in its magnetism. With this in mind, it is noteworthy that the temperature dependence of nuclear spin-relaxation rates (1/T 1 ) in the paramagnetic state above T N1 measured at zero magnetic field can be explained qualitatively by both the SCR theory and the local-moment model.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Interplay between magnetism and band topology in the kagome magnets R Mn 6 Sn 6
Kagome-lattice magnets R Mn 6 Sn 6 recently emerged as a new platform to exploit the interplay between magnetism and topological electronic states. Some of the most exciting features of this family are the dramatic dependence of the easy magnetization direction on the rare-earth specie, despite other magnetic and electronic properties being essentially unchanged, and the kagome geometry of the Mn planes that in principle can generate flat bands and Dirac points; gapping of the Dirac points by spin-orbit coupling has been suggested recently to be responsible for the observed anomalous Hall response in the member TbMn 6 Sn 6 . In this paper, we address both issues with ab initio calculations. We have discovered the significant role played by higher-order crystal-field parameters and rare-earth magnetic anisotropy constants in these systems. Further, we demonstrate that the microscopic origin of rare-earth magnetic anisotropy can also be quantified and understood at various levels: ab initio, phenomenological, and analytical. In particular, using a simple and physically transparent analytical model based on perturbation theory, we are able to explain, with full quantitative agreement, the evolution of rare-earth magnetic anisotropy across the series. We analyze in detail the topological properties of Mn-dominated bands and demonstrate how they emerge from the multiorbital planar kagome model. We further show that, despite this fact, most of the topological features at the Brillouin zone corner K are strongly 3D and therefore cannot explain the observed quasi-2D anomalous Hall effect, while the most pronounced quasi-2D dispersion are too far removed from the Fermi level. By employing self-consistent calculations with ab initio many-body approaches, we demonstrate that the exchange-correlation effects beyond the density functional theory for itinerant Mn- d electrons do not significantly alter the obtained electronic and magnetic structure. Therefore, we conclude that, contrary to previous claims, the most pronounced 2D kagome-derived topological band features bear little relevance to transport in RMn 6 Sn 6 , albeit they may possibly be brought to focus by electron or hole doping.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Role of Magnetic Defects in Tuning Ground States of Magnetic Topological Insulators
Abstract Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi 2 Se 3 ‐based dilute ferromagnetic (FM) TIs and MnBi 2 Te 4 (MBT)‐based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb 2 Te 3 form strong AFM dimer singlets within a quintuple block. The AFM superexchange coupling occurs via Mn–Te–Mn linear bonds and is identical to the AFM coupling between antisite defects and the FM Mn layer in MBT, establishing common interactions in the two materials classes. It is also found that the FM correlations in (Sb 1− x Mn x ) 2 Te 3 are likely driven by magnetic defects in adjacent quintuple blocks across the van der Waals gap. In addition to providing answers to long‐standing questions about the evolution of FM order in dilute TI, these results also show that the evolution of global magnetic order from AFM to FM in Sb‐substituted MBT is controlled by defect engineering of the intrablock and interblock coupling.
36 MATERIALS SCIENCE↗
Breakdown of the scaling relation of anomalous Hall effect in Kondo lattice ferromagnet USbTe
The interaction between strong correlation and Berry curvature is an open territory of in the field of quantum materials. Here we report large anomalous Hall conductivity in a Kondo lattice ferromagnet USbTe which is dominated by intrinsic Berry curvature at low temperatures. However, the Berry curvature induced anomalous Hall effect does not follow the scaling relation derived from Fermi liquid theory. The onset of the Berry curvature contribution coincides with the Kondo coherent temperature. Combined with ARPES measurement and DMFT calculations, this strongly indicates that Berry curvature is hosted by the flat bands induced by Kondo hybridization at the Fermi level. Our results demonstrate that the Kondo coherence of the flat bands has a dramatic influence on the low temperature physical properties associated with the Berry curvature, calling for new theories of scaling relations of anomalous Hall effect to account for the interaction between strong correlation and Berry curvature.
36 MATERIALS SCIENCE↗
Magnetic field induced a b -plane rotation of the Eu magnetic moments in trigonal EuMg 2 Bi 2 and EuMg 2 Sb 2 single crystals below their Néel temperatures
The thermodynamic and electronic-transport properties of trigonal EuMg 2 Bi 2 in ab-plane magnetic fields H x and the A-type antiferromagnetic structure have recently been reported. The Eu magnetic moments with spin S = 7/2 remain locked in the ab plane up to and above the ab-plane critical field $H^{c}_{x}$ = 27.5 kOe at which the Eu moments become parallel to H x . Here additional measurements at low fields are reported that reveal a new spin-reorientation transition at a field H c1 ≈ 465 Oe where the Eu moments remain in the ab plane but become perpendicular to H x . At higher fields, the moments cant toward the field resulting in M ∝ H x up to $H^{c}_{x}$. Similar results are reported from measurements of the magnetic properties of EuMg 2 Sb 2 single crystals, where H c1 ≈ 220 Oe is found. Theory is formulated that models the low-field magnetic behavior of both materials, and the associated anisotropies are calculated. Further, the ab-plane trigonal anisotropy in EuMg 2 Sb 2 is found to be significantly smaller than in EuMg 2 Bi 2 .
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Short-Range Crystalline Order-Tuned Conductivity in Cr 2 Si 2 Te 6 van der Waals Magnetic Crystals
Two-dimensional magnetic materials (2DMMs) are significant not only for studies on the nature of 2D long-range magnetic order but also for future spintronic devices. Of particular interest are 2DMMs where spins can be manipulated by electrical conduction. Whereas Cr 2 Si 2 Te 6 exhibits magnetic order in few-layer crystals, its large band gap inhibits electronic conduction. Here we show that the defect-induced short-range crystal order in Cr 2 Si 2 Te 6 , on the length scale below 0.6 nm, induces a substantially reduced band gap and robust semiconducting behavior down to 2 K that turns to metallic above 10 GPa. Our results in this work will be helpful in designing conducting states in 2DMMs and call for spin-resolved measurement of the electronic structure in exfoliated ultrathin crystals.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
As–Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe–Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering
A novel mixed-valent hybrid chiral and polar compound, Fe 7 As 3 Se 12 (en) 6 (H 2 O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe 5 Se 9 ] chains connected via [As 3 Se 2 ]–Se pentagonal linkers and charge-balancing interstitial [Fe(en) 3 ] 2+ complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and 57 Fe Mössbauer spectroscopy showed the presence of mixed-valent Fe 2+ /Fe 3+ in the Fe–Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by 57 Fe Mössbauer spectroscopy, showing that a fraction of the Fe 3+ /Fe 2+ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe 3+ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. Here, this competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Modeling surface spin polarization on ceria-supported Pt nanoparticles
In this work, we employ density functional theory simulations to investigate possible spin polarization of CeO 2 -(111) surface and its impact on the interactions between a ceria support and Pt nanoparticles. With a Gaussian type orbital basis, our simulations suggest that the CeO 2 -(111) surface exhibits a robust surface spin polarization due to the internal charge transfer between atomic Ce and O layers. In turn, it can lower the surface oxygen vacancy formation energy and enhance the oxide reducibility. We show that the inclusion of spin polarization can significantly reduce the major activation barrier in the proposed reaction pathway of CO oxidation on ceria-supported Pt nanoparticles. For metal-support interactions, surface spin polarization enhances the bonding between Pt nanoparticles and ceria surface oxygen, while CO adsorption on Pt nanoparticles weakens the interfacial interaction regardless of spin polarization. However, the stable surface spin polarization can only be found in the simulations based on the Gaussian type orbital basis. Furthermore, given the potential importance in the design of future high-performance catalysts, our present study suggests a pressing need to examine the surface ferromagnetism of transition metal oxides in both experiment and theory.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Possible unconventional pairing in ( Ca , Sr ) 3 ( Ir , Rh ) 4 Sn 13 superconductors revealed by controlling disorder
Here we study the evolution of temperature-dependent resistivity with added pointlike disorder induced by 2.5 MeV electron irradiation in stoichiometric compositions of the “3-4-13” stannides, (Ca,Sr) 3 (Ir,Rh) 4 Sn 13 . Three of these cubic compounds exhibit a proposed microscopic coexistence of charge density wave (CDW) order and superconductivity (SC), while Ca 3 Rh 4 Sn 13 does not develop CDW order. As expected, the CDW transition temperature T CDW is universally suppressed by irradiation in all three compositions. The superconducting transition temperature, T c , behaves in a more complex manner. In Sr 3 Rh 4 Sn 13 , it increases initially in a way consistent with a direct competition of CDW and SC, but quickly saturates at higher irradiation doses. In the other three compounds, T c is monotonically suppressed by irradiation. The strongest suppression is found in Ca 3 Rh 4 Sn 13 , which does not have CDW order. We further examine this composition by measuring the London penetration depth λ(T), from which we derive the superfluid density. The result unambiguously points to a weak-coupling, full single gap, isotropic superconducting state. Therefore we must explain two seemingly incompatible experimental observations: a single isotropic superconducting gap and a significant suppression of T c by nonmagnetic disorder. We conduct a quantitative theoretical analysis based on a generalized Anderson theorem which points to an unconventional multiband s +– -pairing state where the sign of the order parameter is different on one (or a small subset) of the smaller Fermi surface sheets but remains isotropic and overall fully gapped.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Polaronic Conductivity in Cr 2 Ge 2 Te 6 Single Crystals
We report that intrinsic 2D ferromagnetic semiconductors are an important class of materials for spin-charge conversion applications. Cr 2 Ge 2 Te 6 retains long-range magnetic order in the bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, a series of structural, magnetic, X-ray scattering, electronic, thermal transport and first-principles calculation studies are performed, which reveal that localized electronic charge carriers in Cr 2 Ge 2 Te 6 are dressed by the surrounding lattice and are involved in polaronic transport via hopping that is observed via magnetocrystalline anisotropy. This opens the possibility for manipulation of charge transport in Cr 2 Ge 2 Te 6 —based devices by electron–phonon- and spin–orbit coupling-based tailoring of polaron properties.
2D materials↗