4dtransition metal oxide offers an intriguing puzzle for its electronic and magnetic ground state. They are in the crossover regime of strong spin-orbit interaction (SOI) and electron-electron correlation (U) with quenched orbital angular momentum. Our work unravels the electronic and magnetic ground state of the less investigated 4d3double perovskite ruthenates A2LaRuO6(A = Ca, Ba). The negligible effect of SOI is evident from the bulk magnetic, specific heat measurements, and density functional theory (DFT) calculations, indicating a classical spin-only magnetic ground state (S= 3/2) for the materials. Magnetization measurements show that both materials have long-range antiferromagnetic order with a high degree of magnetic frustration (f≈13-15). Interestingly, a nearT2- behavior is observed in low-Tmagnetic heat capacity measurement, indicating the presence of low-dimensional spin wave excitation and magnetic frustration in both materials. The temperature-dependent resistivity measurements and electronic band structure calculations confirm a conventional Mott insulating ground state in these two systems. Moreover, our experimental investigation and DFT calculations highlight the reason for the nonexistence of Sr2LaRuO6.

Achieving atomically flat and stoichiometric films of chiral antiferromagnets (AFM) with two-dimensional kagome spin lattice structures are crucial for integrating these materials in both established and emerging antiferromagnetic spintronic devices. We report a systematic study of growth and anomalous Hall effect in (111)-oriented noncollinear AFM Mn3+xPt1-x films with varying compositions, for x = 0.09, 0.17, 0.28. Under optimized growth conditions, we obtain stoichiometric and atomically flat epitaxial Mn3Pt (111) films on Si(100) substrate, as evidenced by x-ray reflectivity and scanning probe microscopy. The magnetization measurement showed that epitaxial strain can induce a magnetic phase transition from an incommensurate spin state (T2) at x = 0.09 to a triangular all-in/all-out AFM spin order (T1) at x = 0.17, 0.28. The change in magnetic ground state is evident in the transport characteristics, as the (T1) state shows a robust intrinsic anomalous Hall effect (AHE) persisting to room temperature, in contrast to the (T2) state where AHE is negligible. Our studies reveal a hole-dominated conductance with room temperature anomalous Hall conductivity ranging from 5 to 16 Q-1 cm-1 for x = 0.17 and 0.28, respectively. A scaling law is established, indicating that Hall resistivity is primarily governed by the intrinsic nonvanishing Berry curvature. The experimental observation corroborates the electronic structure calculations, which predicts the massless Dirac states near Fermi level in the bulk band structure, attributed to the presence of nonsymorphic glide symmetry. Additionally, we showed that chemical tuning via Mn doping can stabilize the required T1 noncollinear AFM structure which enhance the topology driven intrinsic AHE.

Ferrimagnetism typically emerges from chemically distinct magnetic ions or the same element at two inequivalent crystallographic sites, rendering unequal moments. In contrast, Ni4Nb2O9 has been recently discovered to show a different mechanism, where identical Ni2 ions with the same ligand coordination develop unequal magnetic moments purely due to differences in local environments. Here, we investigate the microscopic origin of this emergent mechanism through a synergy of powder neutron diffraction, inelastic neutron scattering, and first principle based calculations. We demonstrate that the NiA and NiB sublattices, while sharing the same nominal valence, differ in their magnetic dimensionality NiA forms quasi one dimensional chains with enhanced p d hybridization and a reduced magnetic moment, whereas NiB retains a nearly two-dimensional geometry and a full S 1 moment. Our results underscore the pivotal role of spin dimensionality and local structural distortions in stabilizing ferrimagnetism in systems with electronically equivalent magnetic ions.

The designed heterostructure of two experimentally synthesized and theoretically studied double perovskites Sr2CeIrO6 and Sr2MgIrO6 is investigated using the electronic structure method of the first-principles density functional theory. A half-metallic electronic structure is observed originating from the interfacial Ir site, in contrast to the insulating state that was found in the bulk ingredients. Further, we obtain an AFM ground state which is also supported by the microscopic magnetic exchange interactions analysis. The electronic and magnetic interactions are highly anisotropic in nature. The metallic transport is significantly larger at the in-plane interface layer as compared to that of the out-of-plane, and further shows the signatures of the formation of a two-dimensional (2D) Fermi gas. The impact of spin-orbit coupling (SOC) is crucial as it opens up a pseudogap at EF. Our study also reveals the variation in the impact of SOC for the different layers of Ir present in the heterostructures. Our results influence the understanding of the device engineering utilizing the anisotropic transport at the confined 2D interface in the presence of strong SOC physics.

We employ first-principles density-functional theory to perform a comparative investigation of the effect of the spin-orbit coupling (SOC) on the electronic and magnetic properties of three experimentally synthesized and characterized hexagonal perovskites Sr3MIrO6 (M = Mg, Zn, Cd). The electronic-structure calculations show that in all compounds, Ir is the only magnetically active site in the +4[5d5] configuration, whereas M+2 (M = Cd, Zn, Mg) remains in nonmagnetic states with Cd/Zn and Mg featuring d10 and d0 electronic configurations, respectively. The insulating gap could be opened by switching on the correlation parameter U for Sr3CdrO6 and Sr3ZnIrO6, which qualifies it to be a correlated Mott insulator. However, in the case of Sr3MgIrO6, both U and antiferromagnetic ordering is not enough and the gap could only be opened by including the SOC, which classifies it to fall under the category of a typical SOC Mott insulator. The jeff states are visualized from the orbital-projected band structure. The magnetism is studied from the point of view of exchange interactions and magnetocrystalline anisotropy in the presence of the SOC. We also present the comparative analysis of the renormalized impact of SOC on the three compounds, which shows that all three compounds fall under the intermediate coupling regime, where Sr3MgIrO6 is comparatively closer to the atomic jeff = 12 picture from the others.

We employ first-principles density-functional theory, to perform a comparative investigation of the effect of the spin-orbit coupling (SOC) on the electronic and magnetic properties of three experimentally synthesized and characterized hexagonal perovskites Sr$_3$MIrO$_6$(M=Mg, Zn, Cd). The electronic structure calculations show that in all the compounds, Ir is the only magnetically active site in +4[5$d^5$] configuration, whereas M$^{+2}$ (M=Cd, Zn, Mg), remains in nonmagnetic states with Cd/Zn and Mg featuring $d^{10}$ and $d^{0}$ electronic configurations, respectively. The insulating gap could be opened by switching on the correlation parameter $U$ for Sr$_3$CdrO$_6$ and Sr$_3$ZnIrO$_6$ which qualifies it to be a correlated Mott insulator. However, in the case of Sr$_3$MgIrO$_6$ both $U$ and antiferromagnetic ordering is not enough and the gap could only be opened by including the SOC which classifies it to fall under the category of a typical SOC Mott insulator. The $j_{eff}$ states are visualized from the orbital projected band structure. The magnetism is studied from the point of view of exchange interactions and magnetocrystalline anisotropy in the presence of the SOC. We also present the comparative analysis of the renormalized impact of SOC on the three compounds, which shows that all the three compounds fall under the $intermediate$ coupling regime, where Sr$_3$MgIrO$_6$ is comparatively closer to the atomic $j_{eff}=\frac{1}{2}$ picture from the others.

We report magnetic ground state, dynamical magnetic properties, and the spin Hamiltonian of the twodimensional distorted (J(1)-J(2)) triangular lattice antiferromagnetic (TLAFM) spin-5/2 system Na3Fe(PO4)(2) by neutron diffraction, inelastic neutron scattering (INS), and density-functional-theory (DFT) calculations. The compound Na3Fe(PO4)(2) is characterized by distorted triangular lattice with two different nearest neighbor exchange interactions J(1) and J(2); and having a collinear stripy antiferromagnetic (AFM) ground state. The powder INS spectrum consists of two bands of magnetic excitations (over 0.25-2.0 and 3.0-5.5 meV) with a small energy gap of similar to 0.25 meV, a typical characteristic feature of spin-wave excitations of an ordered magnetic state. We model the experimentally observed features of magnetic excitations by linear spin-wave theory and determine the dominant in-plane magnetic exchange interactions J(1) = -0.31 meV (FM), and J(2) = 0.15 meV (AFM). The values of the exchange interaction constants determined from the INS study and the DFT calculations are in good agreement. Further, the interplanar exchange interaction [J(3) = 0.00003 meV (AFM)] has been estimated to be negligible. By determining the spin Hamiltonian through experimental INS and DFT calculations, we could shed light on the microscopic origin of the collinear stripy AFM ground state and verify the theoretical predicted magnetic phase diagram. Besides, the in-depth calculation of first principles Wannier function provides the exchange interaction mechanism between magnetic Fe ions in Na3Fe(PO4)(2). The present study provides an in-depth knowledge of magnetic ground state, their excitations and the spin-Hamiltonian of Na3Fe(PO4)(2) which is helpful to understand the phase diagram of a distorted TLAFM system in general.

The frustration-induced interplay of competing degrees of freedom and quantum fluctuations can evade long-range magnetic ordering and result in novel quantum states with exotic fractionalized excitations. Herein, a comprehensive investigation of YbTaO4 is carried out, where the magnetic Yb3+ ions form a quasi-twodimensional deformed square lattice. Our studies reveal the absence of long-range magnetic ordering and spin freezing down to 1.8 K. Analysis of magnetization and heat capacity confirms that the Yb3+ ions possess a spin orbit driven effective spin (Jeff) = 1 / 2 state with weak antiferromagnetic interactions in the Kramers doublet ground state. Muon spin relaxation measurements confirm the fluctuating nature of Yb3+ spins, and also indicate a large energy separation between the ground state Kramers doublet state and the first excited state. Additionally, the muon spin relaxation rate reveals a plateau below 30 K owing to depopulation of excited crystal field levels which clearly signifies the development of a J eff = 1 / 2 doublet at low temperatures. Theoretical studies based on density functional theory point out the crucial role of spin orbit coupling (SOC) and support the J eff = 1 / 2 nature of Yb3+ spins. Furthermore, DFT+U calculations with and without the inclusion of SOC indicate that SOC gives rise to an insulating state, thereby suggesting YbTaO4 to be a potential spin orbit driven Mott insulator candidate.

A rare class of square-planar iridate, Cs2Na2IrO4, where isolated IrO4 moieties are oriented orthogonally in the consecutive lattice planes, has been investigated using first-principles calculations. Microscopic magnetic exchange interactions and Wannier function analysis reveals the quasi-two-dimensional antiferromagnetic ground state with moderate mean-field transition temperature, in spite of the absence of long-range structural connectivity via IrO4 moieties. Further magnetic interactions pointed out possible canting of the Ir spins in a complex manner, due to the orthogonally oriented IrO4 planes. The estimated magnetocrystalline anisotropy is significantly large, which is further accentuated by Os doping due to the modification of the electronic configurations and electronic structure of the valence and conduction bands. The phonon modes analysis confirms very weak spin-phonon coupling and reveals the possible mechanism for the evolution of orthogonally oriented IrO4 moieties. The energetics of the muon active sites has been identified to guide the experimental measurements.

The magnetism and magnetocaloric effect in double perovskites is an alluring area of research due to its tunable nature. In particular, the exchange interactions and local ordering of magnetic sublattices are sensitive to the chemical substitution, synthesis/growth conditions, and strain. Here we study the effect of strain on magnetism in Gd2NiMnO6 double perovskite thin films grown using pulsed laser deposition on SrTiO3 (001) substrate. Magnetostructural study finds tensile strain to be the origin of perpendicular magnetic anisotropy in Gd2NiMnO6. Further, the anisotropic nature prevails in magnetocaloric effect as well. Magnetic entropy change along the in-plane direction is observed to be 21.82 J Kg-1 K-1, which reduces to 9.84 J Kg-1 K-1 along the out-of-plane direction. Our theoretical calculation reveals a ferrimagnetic ground state of Gd2NiMnO6. The relative spin orientation of Ni and Mn changes from parallel configuration for strained Gd2NiMnO6 to antiparallel configuration for strain-relaxed Gd2NiMnO6.

This article theoretically explores the formation of dumbbell (DB)-like structures by elemental adsorption on the recently synthesized C3N monolayer. Owing to the repulsion from N atoms, different elements from groups III, IV, and V (B, C, Si, Ge, P, and As) have been examined to form DB-like cages when adsorbed on the opposite sides of the substrate. After establishing the dynamical and thermodynamic stability of these materials, their mechanical durability is analyzed. DBs formed by adatoms like P and As provide the highest in-plane stiffness while that by B exhibits the highest Poisson ratio. The ultimate tensile strain turns out to be quite high (around 18%) for the DB C3NP and C3NAs. Electronic band structure depicts semimetallic and semiconducting characteristics depending on the type of adsorbate that can be further tuned via external strain. Both DB C3NP and C3NAs undergo an indirect-to-direct band gap transition, while the semimetals show band gap opening of the order of meV under applied tension. The presence of space-time inversion symmetry with a well-known effective low-energy tight-binding Hamiltonian easily captures the event of linear band crossings in these materials. The valence orbital theory also nicely explains the origin of Dirac cones as well as the semiconducting indirect band gaps. There is visible anisotropy in the Fermi velocity, which can embrace high values such as 7.5 x 10(5) ms(-1) at a specific direction, and this inhomogeneity measure is remarkably high (around 90%) for the Dirac materials. Electronic transport properties such as carrier-dependent effective mass and mobility also possess anisotropies by their very exotic nature. The findings here highlight a distinct class of 2D carbon nitrides with anisotropic Dirac semimetals and indirect gap semiconductors with plausible synthesis routes, which show great potential in nanodevice applications.

Recent findings of large anomalous Hall signal in nonferromagnetic and nonferrimagnetic materials suggest that the magnetization of the system is not a critical component for the realization of the anomalous Hall effect (AHE). Here, we present a combined theoretical and experimental study demonstrating the evolution of different mechanisms of AHE in a cubic Heusler system MnPt1-xIrxSn. With the help of magnetization and neutron diffraction studies, we show that the substitution of nonmagnetic Ir in place of Pt significantly reduces the net magnetic moment from 4.17 mu B/f.u. in MnPtSn to 2.78 mu B/f.u. for MnPt0.5Ir0.5Sn. In contrast, the anomalous Hall resistivity is enhanced by nearly three times from 1.6 mu Q cm in MnPtSn to about 5 mu Q cm for MnPt0.5Ir0.5Sn. The power law analysis of the Hall resistivity data suggests that the extrinsic contribution of AHE that dominates in the case of the parent MnPtSn almost vanishes for MnPt0.5Ir0.5Sn, where the intrinsic mechanism plays the major role. The experimental results are well supported by our theoretical study, which shows a considerable enhancement of the spin-orbit coupling when Ir is introduced into the system. Our finding of a crossover of the anomalous Hall effect with chemical engineering is a major contribution toward the recent interest in controlling the band topology of topological materials, both in bulk and thin-film forms.

The interplay of spin-orbit coupling (SOC) with the other energy scales gives rise to various novel and interesting quantum phenomena in the Ir based double perovskites. In recent findings the double-perovskites Sr2FeIrO6 (SFIO) and Ca2FeIrO6 (CFIO) have been reported to fall under the category of a SOC driven antiferromagnetic (AFM) Mott insulator. Using density functional theory based first principles calculations, we have performed a comparative electronic structure investigation of these compounds. We reveal the microscopic origin of the difference in the AFM transition temperature observed in the experiments through the calculated exchange interactions and the Wannier functions. We addressed the role of SOC in dictating the ground state properties of these two compounds. Although both of the compounds are isoelectronic and isovalent, however, the effective strength and the impact of SOC is very different and nonmonotonic in these compounds, due to the delicate balance with the other energy scales. Our study advances the understanding of the nontrivial role of SOC in driving ground state magnetic properties of the Ir based oxides in general and explores the opportunities for further designing of the SOC driven quantum phases.

The interplay of spin-orbit coupling (SOC) with the other energy scales gives rise to various novel and interesting quantum phenomena in the Ir based double perovskites. In recent findings the double-perovskites ${\mathrm{Sr}}_{2}{\mathrm{FeIrO}}_{6}$ (SFIO) and ${\mathrm{Ca}}_{2}{\mathrm{FeIrO}}_{6}$ (CFIO) have been reported to fall under the category of a SOC driven antiferromagnetic (AFM) Mott insulator. Using density functional theory based first principles calculations, we have performed a comparative electronic structure investigation of these compounds. We reveal the microscopic origin of the difference in the AFM transition temperature observed in the experiments through the calculated exchange interactions and the Wannier functions. We addressed the role of SOC in dictating the ground state properties of these two compounds. Although both of the compounds are isoelectronic and isovalent, however, the effective strength and the impact of SOC is very different and nonmonotonic in these compounds, due to the delicate balance with the other energy scales. Our study advances the understanding of the nontrivial role of SOC in driving ground state magnetic properties of the Ir based oxides in general and explores the opportunities for further designing of the SOC driven quantum phases.

The 3d-5d based double perovskites offer an ideal playground to study the interplay between electron correlation (U) and spin-orbit coupling (SOC) effect, showing exotic physics. The Sr2FeIrO6 is an interesting member in this family with ionic distribution of Fe3+ (3d(5)) and Ir5+ (5d(4)) where the later is believed to be nonmagnetic under the picture of strong SOC. Here we report a detailed investigation of structural, magnetic, and electronic transport properties along with electronic structure calculations in (Sr1-xCax)(2)FeIrO6 series with x from 0 to 1. While the basic interactions such as U and SOC are unlikely to be modified, a structural modification is expected due to ionic size difference between Sr2+ and Ca2+ which would influence other properties such as crystal field effect and bandwidths. While nonmonotonic changes in lattice parameters are observed across the series, the spectroscopic investigations reveal that 3+/5+ charge state of Fe/Ir continue till the end of the series. An analysis of magnetic data suggests similar nonmonotonic evolution of magnetic parameters with doping. Temperature dependent crystal structure as well as low temperature (5 K) magnetic structure have been determined from neutron powder diffraction measurements which further indicate site ordered moments for both Fe and Ir. The whole series shows insulating behavior with a nonmonotonic variation in resistivity where the charge transport follows the three-dimensional variable range hopping model. The electronic structure calculations show, SOC enhanced, a noncollinear antiferromagnetic and a Mott-type insulating state is the stable ground state for the present series with a substantial amount of orbital moment, but less than the spin magnetic moment, at the Ir site and the magnetocrystalline anisotropy. The calculations further show the evolution of the spin and orbital magnetic moment components across the series along with the magnetization density. The obtained results imply that the local structural modification with introduction of lower size Ca2+ has a large influence on the magnetic and transport properties, further showing a large agreement between experimental results as well as theoretical calculations.

The 3d-5d based double perovskites offer an ideal playground to study the interplay between electron correlation (U) and spin-orbit coupling (SOC) effect, showing exotic physics. The Sr_2FeIrO_6 is an interesting member in this family with ionic distribution of Fe^3+ (3d^5) and Ir^5+ (5d^4) where the later is believed to be nonmagnetic under the picture of strong SOC. Here, we report detailed investigation of structural, magnetic and electronic transport properties along with electronic structure calculations in (Sr_1-xCa_x)_2FeIrO_6 series with x from 0 to 1. While the basic interactions such as, U and SOC are unlikely to be modified but a structural modification is expected due to ionic size difference between Sr^2+ and Ca^2+ which would influence other properties such as crystal field effect and band widths. While a nonmonotonic changes in lattice parameters are observed across the series, the spectroscopic investigations reveal that 3+/5+ charge state of Fe/Ir continue till end of the series. An analysis of magnetic data suggests similar nonmonotonic evolution of magnetic parameters with doping. Temperature dependent crystal structure as well as low temperature (5 K) magnetic structure have been determined from neutron powder diffraction measurements. The whole series shows insulating behavior. The electronic structure calculations show, SOC enhanced, a noncollinear antiferromagnetic and Mott-type insulating state is the stable ground state for present series with a substantial amount of orbital moment, but less than the spin magnetic moment, at the Ir site and the magnetocrystalline anisotropy. The obtained results imply that the Ca^2+ has large influence on the magnetic and transport properties, further showing a large agreement between experimental results as well as theoretical calculations.