Browsing by Author "Oppeneer, P.M."

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Fe-porphyrin on Co(001) and Cu(001): A Comparative Dispersion-augmented Density Functional Theory Study
(2020) Azuri, I.; Ali, M.E.; Tarafder, K.; Oppeneer, P.M.; Kronik, L.
We present a comparative density functional theory (DFT) investigation of the interaction of the iron porphyrin (FeP) molecule with the metallic Co(001) and Cu(001) surfaces, with the aim of elucidating the effect of different choices for the treatment of dispersion. We compare a GGA+U approach, several flavors of dispersion-augmented terms, and two variants of the vdW-DF approach, which treats long-range correlation explicitly. For the Co surface, we find that all approaches predict chemisorption and a high-spin state, although vdW-DF functionals generally predict weaker bonds and weaker chemisorption. For the Cu surface, we find that the functionals augmented by pair-wise dispersion once again predict chemisorption and a preferred HS state, but the vdW-DF functionals predict physisorption and a LS state. These results demonstrate the importance of careful assessment of the level of theory at which dispersion is treated, as this may have significant quantitative and even qualitative effects on the predictions made. The results also call for additional experimental data for these systems. 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Fe-porphyrin on Co(001) and Cu(001): A Comparative Dispersion-augmented Density Functional Theory Study
(Wiley-VCH Verlag info@wiley-vch.de, 2020) Azuri, I.; Ali, M.E.; Tarafder, K.; Oppeneer, P.M.; Kronik, L.
We present a comparative density functional theory (DFT) investigation of the interaction of the iron porphyrin (FeP) molecule with the metallic Co(001) and Cu(001) surfaces, with the aim of elucidating the effect of different choices for the treatment of dispersion. We compare a GGA+U approach, several flavors of dispersion-augmented terms, and two variants of the vdW-DF approach, which treats long-range correlation explicitly. For the Co surface, we find that all approaches predict chemisorption and a high-spin state, although vdW-DF functionals generally predict weaker bonds and weaker chemisorption. For the Cu surface, we find that the functionals augmented by pair-wise dispersion once again predict chemisorption and a preferred HS state, but the vdW-DF functionals predict physisorption and a LS state. These results demonstrate the importance of careful assessment of the level of theory at which dispersion is treated, as this may have significant quantitative and even qualitative effects on the predictions made. The results also call for additional experimental data for these systems. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Interfacial spin manipulation of nickel-quinonoid complex adsorbed on co(001) substrate
(MDPI, 2019) Reddy, I.R.; Oppeneer, P.M.; Tarafder, K.
We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory +U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = 0 in the gas phase to high-spin S ? 1 when adsorbed on the Co(001) surface. A strong covalent interaction of the quinonoid rings and surface atoms leads to an increase of the Ni–O(N) bond lengths in the chemisorbed molecule that support the spin-state switching. Our DFT+U calculations show that the molecule is ferromagnetically coupled to the substrate. The Co surface–Ni center exchange mechanism was carefully investigated. We identified an indirect exchange interaction via the quinonoid ligands that stabilizes the molecule’s spin moment in ferromagnetic alignment with the Co surface magnetization. © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors
(2016) Dhara, B.; Tarafder, K.; Jha, P.K.; Panja, S.N.; Nair, S.; Oppeneer, P.M.; Ballav, N.
Owing to long spin-relaxation time and chemically customizable physical properties, molecule-based semiconductor materials like metal-phthalocyanines offer promising alternatives to conventional dilute magnetic semiconductors/oxides (DMSs/DMOs) to achieve room-temperature (RT) ferromagnetism. However, air-stable molecule-based materials exhibiting both semiconductivity and magnetic-order at RT have so far remained elusive. We present here the concept of supramolecular arrangement to accomplish possibly RT ferromagnetism. Specifically, we observe a clear hysteresis-loop (Hc ? 120 Oe) at 300 K in the magnetization versus field (M-H) plot of the self-assembled ensembles of diamagnetic Zn-phthalocyanine having peripheral F atoms (ZnFPc; S = 0) and paramagnetic Fe-phthalocyanine having peripehral H atoms (FePc; S = 1). Tauc plot of the self-assembled FePc ZnFPc ensembles showed an optical band gap of ?1.05 eV and temperature-dependent current-voltage (I-V) studies suggest semiconducting characteristics in the material. Using DFT+U quantum-chemical calculations, we reveal the origin of such unusual ferromagnetic exchange-interaction in the supramolecular FePc ZnFPc system. 2016 American Chemical Society.
Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors
(American Chemical Society service@acs.org, 2016) Dhara, B.; Tarafder, K.; Jha, P.K.; Panja, S.N.; Nair, S.; Oppeneer, P.M.; Ballav, N.
Owing to long spin-relaxation time and chemically customizable physical properties, molecule-based semiconductor materials like metal-phthalocyanines offer promising alternatives to conventional dilute magnetic semiconductors/oxides (DMSs/DMOs) to achieve room-temperature (RT) ferromagnetism. However, air-stable molecule-based materials exhibiting both semiconductivity and magnetic-order at RT have so far remained elusive. We present here the concept of supramolecular arrangement to accomplish possibly RT ferromagnetism. Specifically, we observe a clear hysteresis-loop (Hc ? 120 Oe) at 300 K in the magnetization versus field (M-H) plot of the self-assembled ensembles of diamagnetic Zn-phthalocyanine having peripheral F atoms (ZnFPc; S = 0) and paramagnetic Fe-phthalocyanine having peripehral H atoms (FePc; S = 1). Tauc plot of the self-assembled FePc···ZnFPc ensembles showed an optical band gap of ?1.05 eV and temperature-dependent current-voltage (I-V) studies suggest semiconducting characteristics in the material. Using DFT+U quantum-chemical calculations, we reveal the origin of such unusual ferromagnetic exchange-interaction in the supramolecular FePc···ZnFPc system. © 2016 American Chemical Society.
Pressure-driven structural and spin-state transition in a Hofmann clathrate coordination polymer
(Elsevier B.V., 2021) Reddy, I.R.; Oppeneer, P.M.; Tarafder, K.
Hofmann-type organometallic frameworks are well known for their porous crystal structure, exhibiting interesting electronic, optical, and magnetic properties, and are therefore considered as promising materials for various technological applications. Here, using density functional theory+U (DFT+U) calculations, we investigate the spin-state transition in a newly synthesized Hofmann clathrate, namely the Fe{OS(CH3)2}2{Ag(CN)2}2 complex, by applying hydrostatic pressure as an external perturbation. Our study reveals that under a relatively low isotropic hydrostatic pressure, the complex exhibits a reversible spin switching, whereas it undergoes a structural phase transition when the pressure is larger and anisotropic. The spin state of the Fe atom in the Hofmann clathrate complex transforms from high spin to intermediate spin state under anisotropic compression of the lattice parameters. The coordination polymer complex remains a magnetic semiconductor after the pressure-driven structural transformation. © 2020 Elsevier B.V.
Route to achieving giant magnetoelectric coupling in BaTiO3/Sr2CoO3 F perovskite heterostructures
(2018) Reddy, I.R.; Oppeneer, P.M.; Tarafder, K.
Polarization-induced spin switching of atoms in magnetic materials opens the possibilities to design and develop advanced spintronic devices, in particular, storage devices where the magnetic state can be controlled by an electric field. We employ density functional theory calculations to study the magnetic properties of a perovskite strontium cobalt oxyfluoride Sr2CoO3F (SCOF) in a hybrid perovskite heterostructure, where SCOF is sandwiched between two ferroelectic BaTiO3 (BTO) layers. Our calculations show that the spin state of the central Co atom in SCOF can be controlled by altering the polarization direction of the BTO, specifically, to switch from a high-spin state to a low-spin state by changing the relative orientation of the ferroelectric polarization of BTO with respect to SCOF, leading to an unexpected, giant magnetoelectric coupling, ?s?21 10-10Gcm2/V. 2018 American Physical Society.
Route to achieving giant magnetoelectric coupling in BaTiO3/Sr2CoO3 F perovskite heterostructures
(American Physical Society revtex@aps.org, 2018) Reddy, I.R.; Oppeneer, P.M.; Tarafder, K.
Polarization-induced spin switching of atoms in magnetic materials opens the possibilities to design and develop advanced spintronic devices, in particular, storage devices where the magnetic state can be controlled by an electric field. We employ density functional theory calculations to study the magnetic properties of a perovskite strontium cobalt oxyfluoride Sr2CoO3F (SCOF) in a hybrid perovskite heterostructure, where SCOF is sandwiched between two ferroelectic BaTiO3 (BTO) layers. Our calculations show that the spin state of the central Co atom in SCOF can be controlled by altering the polarization direction of the BTO, specifically, to switch from a high-spin state to a low-spin state by changing the relative orientation of the ferroelectric polarization of BTO with respect to SCOF, leading to an unexpected, giant magnetoelectric coupling, ?s?21×10-10Gcm2/V. © 2018 American Physical Society.