Publications

2025

1. preprint

   Emergence of topological superconductivity in the presence of chiral magnetism in 2D CrInTe_3

   Arnob Mukherjee^*, Fengyi Zhou, Soheil Ershadrad, Tanay Nag,  Duo Wang , and Biplab Sanyal

   arXiv:2502.07446, Feb 2025

   DOI

2024

1. preprint

   Discovery of an Ultra-Stable Antiferromagnetic Two-Dimensional CrF3 Phase with Anisotropic Quasi-1D Mechanical, Electronic, and Thermal Properties

   Xin Chen, Fengyi Zhou, Yan Suo, Cheng Shao^*,  Duo Wang^* , and Biplab Sanyal^*

   arXiv:2412.19118, Dec 2024

   DOI
2. preprint

   Emergence of insulating ferro-and ferrimagnetism with enhanced optical properties in double-double perovskite oxides

   Monirul Shaikh^*, Fengyi Zhou, Sathyamoorthi Buvaneswaran, Rajan Gowsalya, Trilochan Sahoo,  Duo Wang^* , and Saurabh Ghosh^*

   Nov 2024

   DOI
3. npj 2D Mater.Appl.

   Emergence of polar skyrmions in 2D Janus CrInX3 (X=Se, Te) magnets

   Fengyi Zhou, Monirul Shaikh, Weiwei Sun, Feng Chen , Xin Chen, Shu Li, Henry Tong, Biplab Sanyal^*, and  Duo Wang^*

   npj 2D Materials and Applications, Aug 2024

   Abs DOI

   In the realm of multiferroicity in 2D magnets, whether magnetic and polar skyrmions can coexist within a single topological entity has emerged as an important question. Here, we study Janus 2D magnets CrInX3 (X=Se, Te) for a comprehensive investigation of the magnetic ground state, magnetic excited state, and corresponding ferroelectric polarization by first-principles electronic structure calculations and Monte Carlo simulations. Specifically, we have thoroughly elucidated the magnetic exchange mechanisms, and have fully exemplified the magnetic field dependence of the magnon spectrum. More importantly, our study reveals a previously unrecognized, remarkably large spin-spiral-induced ferroelectric polarization (up to 194.9 μC/m2) in both compounds. We propose an approach to identify polar skyrmions within magnetic skyrmions, based on the observed direct correlation between spin texture and polarization density. Elucidating this correlation not only deepens our understanding of magnetic skyrmions but also paves the way for innovative research in the realm of multiferroic skyrmions.

4. Phys.Rev.B

   Design of magnetic polar double-double perovskite oxides through cation ordering

   Monirul Shaikh^*,  Duo Wang , and Saurabh Ghosh^*

   Physical Review B, May 2024

   Abs DOI

   Starting from the centrosymmetric MnRMnSbO6 compound, we explore the realm of magnetic polar double-double perovskite oxides characterized by significant ferroelectric polarization. Employing symmetry operations, first-principles methodologies, and Monte Carlo simulations, our investigation delves into the structural, magnetic, ferroelectric, and electronic attributes of the polar LaFeMnNiO6 and LaTiMnNiO6 compounds. Structural analysis uncovers that the paraelectric-ferroelectric phase transition is intricately linked to the Fe/Ti displacement of square-planar Fe/TiO4. Notably, the magnetic LaFeMnNiO6 and LaTiMnNiO6 compounds demonstrate robust ferroelectric polarizations, measuring 20.0 and 21.8µC/cm2, respectively, accompanied by minimalist forbidden energy gaps of 1.40 and 1.18 eV using the generalized gradient approximation +U method. Furthermore, we pinpoint elevated magnetic transition temperatures for these compounds. Additionally, our study scrutinizes the energies associated with diverse spin configurations and identifies potential minimum decomposition pathways into stable oxides. This comprehensive analysis ensures the meticulous formation of the LaFeMnNiO6 and LaTiMnNiO6 compounds.

2023

1. Enriching 2D transition metal borides via MB XMenes (M = Fe, Co, Ir): Strong correlation and magnetism

   Jiawei Tang#, Shaohan Li#,  Duo Wang# , Qi Zheng, Jing Zhang, Tao Lu, Jin Yu, Litao Sun, Baisheng Sa, Bobby G. Sumpter, Jingsong Huang, and Weiwei Sun^*

   Nanoscale Horizons, Nov 2023

   Abs DOI

   We explore a series of new 2D magnetic FeSe-like XMene (anti-MXene) borides, among which FeB exhibits a stable ferromagnetic state with notable MAE and a high Curie temperature, indicating its potential for spintronic applications.

2. Appl.Phys.Lett.

   Giant spin-splitting and tunable spin-momentum locked transport in room temperature collinear antiferromagnetic semimetallic CrO monolayer

   Xin Chen,  Duo Wang , Linyang Li^*, and Biplab Sanyal^*

   Applied Physics Letters, Jul 2023

   Abs DOI

   In this work, we present theoretical predictions of a two-dimensional collinear antiferromagnetic semimetal, CrO, which exhibits a giant spin-split band structure, spin-momentum locked transport properties, and a high Néel temperature. Specifically, CrO features two pairs of spin-polarized anisotropic Weyl points at the Fermi level. By manipulating the position of these Weyl points with strain, we demonstrate that four different antiferromagnetic spintronic states with zero net magnetic moments can be achieved, including semimetals with two spin-polarized transport channels, half-semimetals, semiconductors with two spin-polarized transport channels, and half-semiconductors. The strain-induced semiconducting state also preserves the ultra-high carrier mobility of Weyl points, and the bandgap can be easily tuned. These findings offer a good avenue in spintronics without net magnetic moment or strong spin–orbit coupling and could lead to the development of antiferromagnetic materials for spintronic applications.

3. Phys.Rev.B

   Orthorhombic distortion drives orbital ordering in the antiferromagnetic 3d1 Mott insulator PrTiO3

   Prithwijit Mandal^*, Shashank Kumar Ojha,  Duo Wang , Ranjan Kumar Patel, Siddharth Kumar, Jyotirmay Maity, Zhan Zhang , Hua Zhou, Christoph Klewe, Padraic Shafer, Biplab Sanyal^*, and Srimanta Middey^*

   Physical Review B, Jul 2023

   Abs DOI

   The orbital, which represents the shape of the electron cloud, very often strongly influences the manifestation of various exotic phenomena, e.g., magnetism, metal-insulator transition, colossal magnetoresistance, unconventional superconductivity, etc. in solid-state systems. The observation of the antiferromagnetism in RETiO3 (RE=rare-earth) series has been puzzling since the celebrated Kugel-Khomskii model of spin-orbital superexchange predicts ferromagnetism in an orbitally degenerate d1 system. Further, the existence of the orbitally ordered vs. orbital liquid phase in both antiferromagnetic and paramagnetic phase have been unsettled issues thus far. To address these longstanding questions, we investigate single crystalline film of PrTiO3. Our synchrotron x-ray diffraction measurements confirm the retention of bulklike orthorhombic (D2h) symmetry in the thin film geometry. We observe similar x-ray linear dichroism signal in both paramagnetic and antiferromagnetic phase, which can be accounted by ferro-orbital ordering (FOO). While the presence of D2h crystal field does not guarantee lifting of orbital degeneracy always, we find it to be strong enough in these rare-earth titanates, leading to the FOO state. Thus, our work demonstrates the orthorhombic distortion is the driving force for the orbital ordering of antiferromagnetic RETiO3.

2022

1. Phys.Rev.B

   Strain-driven antiferromagnetic exchange interaction in SrMnO3 probed by phase-shifted spin Hall magnetoresistance

   J J L van Rijn^*,  D Wang , B Sanyal, and T Banerjee^*

   Physical Review B, Dec 2022

   Abs DOI

   Multiferroics have found renewed interest in topological magnetism and for logic-in-memory applications. Among them, SrMnO3, possessing strong magnetoelectric coupling, is gaining attention for the design of coex- isting magnetic and polar orders upon straining. Here we demonstrate antiferromagnetic exchange interactions in strained SMO thin films extracted from a new feature in the phase response of spin Hall magnetoresistance, which has not been explored in earlier works, such as in magnetic insulators. We explain our findings with a model that incorporates magnetic anisotropy along the [110] direction, corroborates with density functional theory studies, and is consistent with the direction of ferroelectric polarization in SrMnO3. The fundamental insights obtained from our studies establishes the potential of this material in magnetoelectrically coupled devices for different logic and memory applications

2. J.Phys.Chem.Lett.

   Unusual Magnetic Features in Two-Dimensional Fe5GeTe2 Induced by Structural Reconstructions

   Soheil Ershadrad#, Sukanya Ghosh#,  Duo Wang , Yaroslav Kvashnin, and Biplab Sanyal^*

   The Journal of Physical Chemistry Letters, May 2022

   Abs DOI

   Recent experiments on Fe5GeTe2 suggested the presence of a symmetry breaking of its conventional crystal structure. Here, using density functional theory calculations, we elucidate that the stabilization of the (√3 × √3)R30° supercell structure is caused by the swapping of Fe atoms occurring in the monolayer limit. The swapping to the vicinity of Te atoms is facilitated by the spontaneous occurrence of Fe vacancy and its low diffusion barrier. Our calculated magnetic exchange parameters show the simultaneous presence of ferromagnetic and antiferromagnetic exchange among a particular type of Fe atom. The Fe sublattice projected magnetization obtained from Monte Carlo simulations clearly demonstrates an exotic temperature-dependent behavior of this Fe type along with a large canting angle at T = 0 K, indicating the presence of a complex noncollinear magnetic order. We propose that the low-temperature crystal structure results from the swapping between two sublattices of Fe, giving rise to peculiar magnetization obtained in experiments.

2021

1. Phys.Rev.B

   Unraveling complex magnetism in two-dimensional FeS2

   Duo Wang^* , Xin Chen^*, and Biplab Sanyal^*

   Physical Review B, Dec 2021

   Abs DOI

   Atomically thin two-dimensional (2D) magnets have given rise to emergent phenomena due to magnetic exchange and spin-orbit coupling showing great promise for realizing ultrathin device structures. In this paper, we critically examine the magnetic properties of 2D FeS2, a non van der Waals magnet, which has been recently claimed to exhibit room-temperature ferromagnetism in the (111) orientation. Our ab initio study based on collinear density functional theory has revealed the ground state as an antiferromagnetic one with an ordering temperature of around 100 K along with a signature of spin-phonon coupling, which may trigger a ferromagnetic coupling via strain. Moreover, our calculations based on spin spirals indicate the possibility of noncollinear magnetic structures, which is also supported by Monte Carlo simulations based on ab initio magnetic exchange parameters. This opens up an excellent possibility to manipulate magnetic structures by the application of directional strain.

2. J.Phys.Chem.C

   Systematic Study of Monolayer to Trilayer CrI3: Stacking Sequence Dependence of Electronic Structure and Magnetism

   Duo Wang , and Biplab Sanyal^*

   The Journal of Physical Chemistry C, Aug 2021

   Abs DOI

   In recent years, two-dimensional magnetic materials have attracted a lot of attention due to their unique magnetic properties, which can be manipulated by various degrees of freedom in a van der Waals stacked heterostructure, where different interlayer stackings affect the properties in different ways by exploiting weak interlayer interactions. An interesting example is CrI3, where the interlayer magnetic coupling can be determined by the stacking sequence. Here we present a systematic study of the magnetic properties of monolayer, bilayer, and trilayer CrI3 by using density functional theory and Monte Carlo simulations. The effects of different stacking sequences and the number of layers on the magnetic interaction in multilayer CrI3 have been critically analyzed. We have found that the antiferromagnetic interlayer coupling occurs with specific interlayer shifting, while intralayer exchange interactions increase with the number of layers. It is noteworthy that interlayer interactions are independent of the number of layers, whereas the magnetic ordering temperature rises with the increasing number of layers. Moreover, we present the Curie temperatures obtained from Monte Carlo simulations and adiabatic magnon spectra for all the stacking sequences considered here.

3. Phys.Rev.Materials

   Prediction of half-metallic ferrimagnetic quadruple perovskites ACu3Fe2Re2O12 (A=Ca, Sr, Ba, Pb, Sc, Y, La) with high Curie temperatures

   Duo Wang , Monirul Shaikh, Saurabh Ghosh, and Biplab Sanyal^*

   Physical Review Materials, May 2021

   Abs DOI

   A- and B-site ordered quadruple perovskites with the chemical formula AA3′B2B2′O12 can form with 1:3 ratio at the A site. A unique feature of this specially ordered perovskite is that three different atomic sites (A′, B, and B′ sites) can all accommodate magnetic transition metals. As a consequence, multiple magnetic and electronic interactions can occur at A′, B, and/or B′ sites, giving rise to a series of intriguing physical phenomena. CaCu3Fe2Re2O12 is a good example, which shows half-metallic electronic structure, large magnetization, and a very high Curie temperature. Here we investigated a series of ferrimagnetic (FiM) compounds ACu3Fe2Re2O12 (A=Ca, Sr, Ba, Pb, Sc, Y, La) by using density functional theory and Monte Carlo simulations. We found that all compounds with A2+ ions exhibit high Curie temperatures (above 405 K), and the compounds with A3+ substitution yield even higher TC (above 502 K). By examining interatomic exchange parameters, we found that the antiferromagnetic exchange couplings between Re and Cu as well as Re and Fe are responsible for this very high Curie temperature. For the compounds with A3+ substitution, electron doping in bands around the Fermi level dominated by the Re ions strengthens the Re-Cu, Re-Fe, and Re-Re exchange interactions, which cause an increase in the critical temperature. Finally, we calculated the formation energies of the quadruple perovskites with respect to the possible decomposition pathways and have found that the values are reasonable for the synthesis of these compounds under the conditions of high pressure and high temperature. In summary, this work demonstrates a design strategy of enhancing the spin ordering temperature by replacing A-site nonmagnetic ions.

2020

1. Partial cation ordering, relaxor ferroelectricity, and ferrimagnetism in Pb(Fe1 − xYbx)2/3W1/3O3 solid solutions

   S. A. Ivanov, D. C. Joshi, A. A. Bush,  D. Wang , B. Sanyal, O. Eriksson, P. Nordblad, and R. Mathieu^*

   Journal of Applied Physics, Oct 2020

   Abs DOI

   The structural, magnetic, and dielectric properties of ceramic samples of Yb-doped PbFe2/3W1/3O3 have been investigated by a variety of methods including x-ray powder diffraction, magnetometry, and dielectric spectroscopy. In addition, theoretical investigations were made using first-principles density functional calculations. All the doped samples Pb(Fe1 − xYbx)2/3W1/3O3 (PFYWO) (0.1 ≤ x ≤ 0.5) were found to crystallize in an ordered cubic ( F m 3 ¯ m ) structure with partial ordering in the B-perovskite sites. Observed changes in the cationic order were accompanied by differences in the dielectric and magnetic responses of the system. While pure PbFe2/3W1/3O3 is antiferromagnetic, the doped Pb(Fe1 − xYbx)2/3W1/3O3 PFYWO samples display excess moments and ferrimagnetic-like behavior, associated with differences in B′ and B″ site occupancies of the magnetic Fe3+ cations. The magnetic transition temperature of the ferrimagnetic phase is found to decrease with increasing Yb content, from TN ∼350 K of the undoped sample down to 137 K for x = 0.5. All PFYWO compounds display a ferroelectric relaxor behavior akin to that of PbFe2/3W1/3O3, albeit our results show significant changes of the frequency and temperature dependence of the dielectric properties. The changes of the properties of PFYWO with increasing Yb substitution can be explained by the changes in the cation size/charge mismatch and the size difference of the two ordered positions.

2. J.Phys.Chem.Lett.

   Two-Dimensional Square‑A2B (A = Cu, Ag, Au, and B = S, Se): Auxetic Semiconductors with High Carrier Mobilities and Unusually Low Lattice Thermal Conductivities

   Xin Chen^*,  Duo Wang , Xiaobiao Liu, Linyang Li^*, and Biplab Sanyal^*

   The Journal of Physical Chemistry Letters, Mar 2020

   Abs DOI

   Using evolutionary structure search combined with ab initio theory, we investigate the electronic, thermal, and mechanical properties of two-dimensional (2D) A2B (A = Cu, Ag, Au, and B = S, Se) auxetic semiconductors. Two types of structures are found to have low energy, namely, s­(I/II)-A2B, which have direct bandgaps in the range 1.09–2.60 eV and high electron mobilities. Among these semiconductors, Cu2B and Ag2B have light holes with 2 orders of magnitude larger mobility than the heavy holes, up to 9.51 × 104 cm2 V–1 s–1, giving the possibility of achieving highly anisotropic hole transport with the application of a uniaxial strain. Due to the ionic bonding nature, s-A2B structures have unusually low lattice thermal conductivities down to 1.5 W m–1 K–1 at 300 K, which are quite promising for new generation thermoelectric devices. Besides, s-A2B structures show extraordinary flexibility with ultralow Young’s moduli (down to 20 N/m), which are lower than most previously reported 2D materials. Moreover, under strain along the diagonal direction, five of the structures have in-plane negative Poisson’s ratios.

2019

1. Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1−xScx)2∕3W1∕3O3 solid solutions

   Sergey A. Ivanov, Premysl Beran, Alexandr A. Bush, Tapati Sarkar, Samrand Shafeie,  Duo Wang , Biplab Sanyal, Olle Eriksson, Martin Sahlberg, Yaroslav Kvashnin, Roland Tellgren, Per Nordblad, and Roland Mathieu^*

   The European Physical Journal B, Aug 2019

   Abs DOI

   Ceramic samples of the multiferroic perovskite Pb(Fe1−xScx)2∕3W1∕3O3 with 0 ≤ x ≤ 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3̅m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B′ and B′′ sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2∕3W1∕3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B′ and B′′ sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1−xScx)2∕3W1∕3O3 and possibly also in the undoped PbFe2∕3W1∕3O3.

2. Density functional study of structural, electronic and magnetic properties of new half-metallic ferromagnetic double perovskite Sr2MnVO6

   Neda Rahmani, M E Ghazi^*, Morteza Izadifard,  Duo Wang , Alireza Shabani, and Biplab Sanyal

   Journal of Physics: Condensed Matter, Aug 2019

   Abs DOI

   In this paper, a new half-metallic (HM) double perovskite compound is predicted with the simultaneous presence of ferromagnetism and polar distortion. The structural, electronic and magnetic properties of Sr2MnVO6 (SMVO) are calculated by density functional theory (DFT) with both generalized gradient approximation (GGA) and GGA + U approaches, where U is the on-site Coulomb interaction parameter. Different orderings of B (B’) cationic sites in A2BB’O6 double perovskite structure are evaluated, including rocksalt, columnar and layered arrangements for cubic, monoclinic and tetragonal crystal structures. It is found that the most stable ordering is obtained when B and B’ are placed in a layered type ordering for a tetragonal crystal structure with I4/m space group, which is confirmed by phonon calculations. The B-site ordering of the Mn3+ and V5+ ions in a layered configuration leads to ferromagnetically coupled magnetic moments of 4.17 µ B at Mn site and 0.23 µ B at V site. Finally, SMVO is found to be a half-metallic ferromagnetic (HM-FM) compound with a band gap of 0.65 eV in a spin down channel with off-centered displacement of V atoms in the octahedral cage (second order Jahn -Teller effect) which can cause ferroelectricity. Therefore, SMVO is predicted to be a polar HM material and a promising candidate for multiferroic property with potential application in spintronics.

2018

1. Nickel–Copper Alloy Encapsulated in Graphitic Carbon Shells as Electrocatalysts for Hydrogen Evolution Reaction

   Yi Shen^* , Yongfang Zhou,  Duo Wang , Xi Wu, Jia Li^*, and Jingyu Xi

   Advanced Energy Materials, Sep 2018

   Abs DOI

   Searching for cost-effective and high-performance electrocatalysts for hydrogen production is of paramount importance. Herein, nickel-copper (NiCu) alloy nanoparticles are encapsulated into graphitic shells via an ambient-pressure chemical vapor deposition process. The resulting carbon-encapsulated NiCu (denoted as NiCu@C) composite possesses a well-defined core–shell structure with tunable thicknesses of the shells and is examined as electrocatalysts for the hydrogen evolution reaction (HER) in acidic, neutral, and alkaline solutions. Electrochemical measurements indicate that the activity of the NiCu@C highly depends on the thickness of the shell. Single-layered graphene encapsulated NiCu nanoparticles show remarkable HER activity and durability. To obtain a current density of 10 mA cm−2, overpotentials of 48, 164, and 74 mV are needed in electrolyte solutions with pH = 0, 7, and 14, respectively. Such low overpotentials render the composite as one of the most active nonprecious electrocatalysts. Accelerated durability tests demonstrate that the NiCu@C catalysts exhibit excellent stability. Density function theory calculations are conducted to investigate the electronic structures of the NiCu@C. It is found that the representative Ni43Cu12@C240 model shows an ideal adsorption energy of hydrogen (−0.03 eV), manifesting its high HER activity.