Docente
CBPF
Ramon Cardias Alves de Almeida
Publicações
2025
Cardias, Ramon; Strand, Hugo U. R.; Bergman, Anders; Klautau, A. B.; Rappoport, Tatiana G.
Real-space first-principles approach to orbitronic phenomena in metallic multilayers Miscellaneous
2025.
@misc{cardias2025realspacefirstprinciplesapproachorbitronic,
title = {Real-space first-principles approach to orbitronic phenomena in metallic multilayers},
author = {Ramon Cardias and Hugo U. R. Strand and Anders Bergman and A. B. Klautau and Tatiana G. Rappoport},
url = {https://arxiv.org/abs/2508.14270},
year = {2025},
date = {2025-08-19},
urldate = {2025-01-01},
abstract = {We develop a real-space first-principles method based on density functional theory to investigate orbitronic phenomena in complex materials. Using the Real-Space Linear Muffin-Tin Orbital method within the Atomic Sphere Approximation (RS-LMTO-ASA) combined with a Chebyshev polynomial expansion of the Green's functions, we compute orbital (spin) Hall transport and orbital (spin) accumulation directly in real space. The approach scales linearly with system size and naturally incorporates disorder, finite-size effects, and interface roughness. We apply the method to transition-metal-based heterostructures and demonstrate the emergence of substantial orbital (spin) accumulation, even in centrosymmetric systems. Our methodology provides a scalable and flexible framework for realistic simulations of orbital transport phenomena in complex heterostructures.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
We develop a real-space first-principles method based on density functional theory to investigate orbitronic phenomena in complex materials. Using the Real-Space Linear Muffin-Tin Orbital method within the Atomic Sphere Approximation (RS-LMTO-ASA) combined with a Chebyshev polynomial expansion of the Green's functions, we compute orbital (spin) Hall transport and orbital (spin) accumulation directly in real space. The approach scales linearly with system size and naturally incorporates disorder, finite-size effects, and interface roughness. We apply the method to transition-metal-based heterostructures and demonstrate the emergence of substantial orbital (spin) accumulation, even in centrosymmetric systems. Our methodology provides a scalable and flexible framework for realistic simulations of orbital transport phenomena in complex heterostructures.
Cardias, Ramon; Bergman, Anders; Strand, Hugo U. R.; Muniz, R. B.; Costa, Marcio
Noncollinear Edge Magnetism in Nanoribbons of Fe_3GeTe_2 and Fe_3GaTe_2 Journal Article
Em: Nano Lett., 2025, ISSN: 1530-6992.
@article{Cardias2025,
title = {Noncollinear Edge Magnetism in Nanoribbons of Fe_3GeTe_2 and Fe_3GaTe_2},
author = {Ramon Cardias and Anders Bergman and Hugo U. R. Strand and R. B. Muniz and Marcio Costa},
doi = {10.1021/acs.nanolett.5c01890},
issn = {1530-6992},
year = {2025},
date = {2025-07-23},
urldate = {2025-07-23},
journal = {Nano Lett.},
publisher = {American Chemical Society (ACS)},
abstract = {Fe3GeTe2 and Fe3GaTe2 are ferromagnetic conducting materials of van der Waals type with unique magnetic properties that are highly promising for the development of new spintronic, orbitronic, and magnonic devices. Even in the form of two-dimensional-like ultrathin films, they exhibit a relatively high Curie temperature, magnetic anisotropy perpendicular to the atomic planes, and multiple types of Hall effects. We explore nanoribbons made from single layers of these materials and show that they display noncollinear magnetic ordering at their edges. This magnetic inhomogeneity allows angular momentum currents to generate magnetic torques at the sample edges, regardless of their polarization direction, significantly enhancing the effectiveness of magnetization manipulation in these systems. We also demonstrate that it is possible to rapidly reverse the magnetization direction of these nanostructures by means of spin–orbit and spin-transfer torques with rather low current densities, making them quite propitious for nonvolatile magnetic memory units.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fe3GeTe2 and Fe3GaTe2 are ferromagnetic conducting materials of van der Waals type with unique magnetic properties that are highly promising for the development of new spintronic, orbitronic, and magnonic devices. Even in the form of two-dimensional-like ultrathin films, they exhibit a relatively high Curie temperature, magnetic anisotropy perpendicular to the atomic planes, and multiple types of Hall effects. We explore nanoribbons made from single layers of these materials and show that they display noncollinear magnetic ordering at their edges. This magnetic inhomogeneity allows angular momentum currents to generate magnetic torques at the sample edges, regardless of their polarization direction, significantly enhancing the effectiveness of magnetization manipulation in these systems. We also demonstrate that it is possible to rapidly reverse the magnetization direction of these nanostructures by means of spin–orbit and spin-transfer torques with rather low current densities, making them quite propitious for nonvolatile magnetic memory units.
Bezerra-Neto, M. M.; Kvashnin, Y. O.; Bergman, A.; Cardias, R.; Muniz, R. B.; Eriksson, O.; Katsnelson, M. I.; Klautau, A. B.
Chiral spin and orbital angular momentum textures in Mn chains on W(110): Interplay of spin-orbit coupling and crystal-field effects Journal Article
Em: Phys. Rev. B, vol. 112, não 1, 2025, ISSN: 2469-9969.
@article{Bezerra-Neto2025,
title = {Chiral spin and orbital angular momentum textures in Mn chains on W(110): Interplay of spin-orbit coupling and crystal-field effects},
author = {M. M. Bezerra-Neto and Y. O. Kvashnin and A. Bergman and R. Cardias and R. B. Muniz and O. Eriksson and M. I. Katsnelson and A. B. Klautau},
doi = {10.1103/s6b9-djks},
issn = {2469-9969},
year = {2025},
date = {2025-07-21},
journal = {Phys. Rev. B},
volume = {112},
number = {1},
publisher = {American Physical Society (APS)},
abstract = {Stabilization of unusual spin-orbit-driven magnetic orderings are achieved for chains of Mn atoms deposited on a W(110) substrate. First-principles electronic structure calculations show that the ground-state spin configuration is noncollinear, forming chiral spiral-like structures, driven by competing nearest- and next-nearest-neighbor interactions. The orbital magnetic moments are also found to exhibit noncollinear ordering that, interestingly, tend to align in-plane for some systems with an orientation distinctly differently from that of the spin moment. We analyze the mechanism behind such behavior, and find that it is due to the competition between the spin-orbit interaction and crystal-field splitting. Model calculations based on this assumption reproduce the main findings observed in our first-principles calculations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Stabilization of unusual spin-orbit-driven magnetic orderings are achieved for chains of Mn atoms deposited on a W(110) substrate. First-principles electronic structure calculations show that the ground-state spin configuration is noncollinear, forming chiral spiral-like structures, driven by competing nearest- and next-nearest-neighbor interactions. The orbital magnetic moments are also found to exhibit noncollinear ordering that, interestingly, tend to align in-plane for some systems with an orientation distinctly differently from that of the spin moment. We analyze the mechanism behind such behavior, and find that it is due to the competition between the spin-orbit interaction and crystal-field splitting. Model calculations based on this assumption reproduce the main findings observed in our first-principles calculations.
Dugato, Danian A.; Jalil, Wesley B. F.; Cardias, Ramon; Albuquerque, Marcelo; Costa, Marcio; Almeida, Trevor P.; Fallon, Kayla; Kovács, András; McVitie, Stephen; Dunin-Borkowski, Rafal E.; Garcia, Flavio
Curved Nanomagnets: An Archetype for the Skyrmionic States at Ambient Conditions Journal Article
Em: Nano Lett., 2025, ISSN: 1530-6992.
@article{Dugato2025,
title = {Curved Nanomagnets: An Archetype for the Skyrmionic States at Ambient Conditions},
author = {Danian A. Dugato and Wesley B. F. Jalil and Ramon Cardias and Marcelo Albuquerque and Marcio Costa and Trevor P. Almeida and Kayla Fallon and András Kovács and Stephen McVitie and Rafal E. Dunin-Borkowski and Flavio Garcia},
doi = {10.1021/acs.nanolett.5c00773},
issn = {1530-6992},
year = {2025},
date = {2025-04-10},
urldate = {2025-04-10},
journal = {Nano Lett.},
publisher = {American Chemical Society (ACS)},
abstract = {Stabilizing magnetic skyrmions is a critical issue in spintronics, impacting data storage and computing. This study investigates skyrmion and skyrmionium phenomena within a hexagonal array of curved nanomagnets. Utilizing atomistic calculations, micromagnetic simulations, and experimental methods such as magnetic force microscopy and electron holography, we analyze the interplay between magnetic parameters, curvature, and the interfacial Dzyaloshinskii–Moriya interaction (iDMI) in the formation of these structures. We observed that isolated skyrmions and mixed skyrmionic phases can spontaneously form in a symmetric Pt/Co/Pt multilayer curved nanomagnet matrix without external fields at room temperature. Our findings highlight the considerable influence of geometric curvature on iDMI, providing insights for engineering skyrmionic configurations. This research enhances our understanding of nanomagnetism and contributes to the advancement of skyrmion-based technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Stabilizing magnetic skyrmions is a critical issue in spintronics, impacting data storage and computing. This study investigates skyrmion and skyrmionium phenomena within a hexagonal array of curved nanomagnets. Utilizing atomistic calculations, micromagnetic simulations, and experimental methods such as magnetic force microscopy and electron holography, we analyze the interplay between magnetic parameters, curvature, and the interfacial Dzyaloshinskii–Moriya interaction (iDMI) in the formation of these structures. We observed that isolated skyrmions and mixed skyrmionic phases can spontaneously form in a symmetric Pt/Co/Pt multilayer curved nanomagnet matrix without external fields at room temperature. Our findings highlight the considerable influence of geometric curvature on iDMI, providing insights for engineering skyrmionic configurations. This research enhances our understanding of nanomagnetism and contributes to the advancement of skyrmion-based technologies.
Cardias, R.; Bergman, Anders; Strand, Hugo U. R.; Muniz, R. B.; Costa, Marcio
Edge non-collinear magnetism in nanoribbons of Fe3GeTe2 and Fe3GaTe2 Working paper
2025.
@workingpaper{cardias2025edgenoncollinearmagnetismnanoribbons,
title = {Edge non-collinear magnetism in nanoribbons of Fe3GeTe2 and Fe3GaTe2},
author = {R. Cardias and Anders Bergman and Hugo U. R. Strand and R. B. Muniz and Marcio Costa},
url = {https://arxiv.org/abs/2502.12356},
year = {2025},
date = {2025-02-17},
urldate = {2025-01-01},
abstract = {Fe3GeTe2 and Fe3GaTe2 are ferromagnetic conducting materials of van der Waals-type with unique magnetic properties that are highly promising for the development of new spintronic, orbitronic and magnonic devices. Even in the form of two-dimensional-like ultrathin films, they exhibit relatively high Curie temperature, magnetic anisotropy perpendicular to the atomic planes and multiple types of Hall effects. We explore nanoribbons made from single layers of these materials and show that they display non-collinear magnetic ordering at their edges. This magnetic inhomogeneity allows angular momentum currents to generate magnetic torques at the sample edges, regardless of their polarization direction, significantly enhancing the effectiveness of magnetization manipulation in these systems. We also demonstrate that it is possible to rapidly reverse the magnetization direction of these nanostructures by means of spin-orbit and spin-transfer torques with rather low current densities, making them quite propitious for non-volatile magnetic memory units.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
Fe3GeTe2 and Fe3GaTe2 are ferromagnetic conducting materials of van der Waals-type with unique magnetic properties that are highly promising for the development of new spintronic, orbitronic and magnonic devices. Even in the form of two-dimensional-like ultrathin films, they exhibit relatively high Curie temperature, magnetic anisotropy perpendicular to the atomic planes and multiple types of Hall effects. We explore nanoribbons made from single layers of these materials and show that they display non-collinear magnetic ordering at their edges. This magnetic inhomogeneity allows angular momentum currents to generate magnetic torques at the sample edges, regardless of their polarization direction, significantly enhancing the effectiveness of magnetization manipulation in these systems. We also demonstrate that it is possible to rapidly reverse the magnetization direction of these nanostructures by means of spin-orbit and spin-transfer torques with rather low current densities, making them quite propitious for non-volatile magnetic memory units.
2024
Dugato, Danian A.; Jalil, Wesley; Cardias, Ramon; Albuquerque, Marcelo; Costa, Marcio; Garcia, Flavio
Curved Nanomagnets: An Experimental Archetype for Skyrmion Stabilization Working paper
Research Square, 2024.
@workingpaper{Dugato2024,
title = {Curved Nanomagnets: An Experimental Archetype for Skyrmion Stabilization},
author = {Danian A. Dugato and Wesley Jalil and Ramon Cardias and Marcelo Albuquerque and Marcio Costa and Flavio Garcia},
url = {https://www.researchsquare.com/article/rs-4547588/v1},
doi = {10.21203/rs.3.rs-4547588/v1},
year = {2024},
date = {2024-06-10},
urldate = {2024-06-10},
publisher = {Research Square Platform LLC},
abstract = {In the fields of nanomagnetism and spintronics, the controlled stabilization of mag- netic skyrmions is a topic of great interest for potential applications in data storage and innovative computing systems. This study delves into the intriguing phenomenon of skyrmions on a hexagonal array of curved nanomagnets. Through a combination of atomistic calculation, micromagnetic simulations, and experimental observations, we thoroughly explore the intricate interplay between magnetic parameters, curvature, and interfacial Dzyaloshinskii-Moriya interaction (iDMI) in the formation of these topolog- ically non-trivial magnetic structures. We have observed the spontaneous formation of isolated skyrmions (<150 nm) on a curved nanomagnet matrix of symmetric Pt/Co/Pt multilayer without the necessity of applied fields. Our research sheds light on the pro- found impact of geometric curvature on iDMI, offering invaluable insights for engi- neering and controlling skyrmionic configurations. This work advances nanomagnetism knowledge and sets the stage for designing skyrmion-based technologies.},
howpublished = {Research Square},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
In the fields of nanomagnetism and spintronics, the controlled stabilization of mag- netic skyrmions is a topic of great interest for potential applications in data storage and innovative computing systems. This study delves into the intriguing phenomenon of skyrmions on a hexagonal array of curved nanomagnets. Through a combination of atomistic calculation, micromagnetic simulations, and experimental observations, we thoroughly explore the intricate interplay between magnetic parameters, curvature, and interfacial Dzyaloshinskii-Moriya interaction (iDMI) in the formation of these topolog- ically non-trivial magnetic structures. We have observed the spontaneous formation of isolated skyrmions (<150 nm) on a curved nanomagnet matrix of symmetric Pt/Co/Pt multilayer without the necessity of applied fields. Our research sheds light on the pro- found impact of geometric curvature on iDMI, offering invaluable insights for engi- neering and controlling skyrmionic configurations. This work advances nanomagnetism knowledge and sets the stage for designing skyrmion-based technologies.
2023
Cardias, Ramon; Silva, Jhonatan Santos; Bergman, Anders; Szilva, Attila; Kvashnin, Yaroslav O.; Fransson, Jonas; Klautau, Angela B.; Eriksson, Olle; Delin, Anna; Nordström, Lars
2023.
@workingpaper{cardias2023unraveling,
title = {Unraveling the connection between high-order magnetic interactions and local-to-global spin Hamiltonian in non-collinear magnetic dimers},
author = {Ramon Cardias and Jhonatan Santos Silva and Anders Bergman and Attila Szilva and Yaroslav O. Kvashnin and Jonas Fransson and Angela B. Klautau and Olle Eriksson and Anna Delin and Lars Nordström},
url = {https://arxiv.org/abs/2306.07222},
doi = {10.48550/arXiv.2306.07222},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
abstract = {A spin Hamiltonian, which characterizes interatomic interactions between spin moments, is highly valuable in predicting and comprehending the magnetic properties of materials. A deeper understanding of the microscopic origin of magnetic interactions can open new pathways toward realizing nanometer-scale systems for future spintronic devices. Here, we explore a method for explicitly calculating interatomic exchange interactions in non-collinear configurations of magnetic materials considering only a bilinear spin Hamiltonian in a local scenario. Based on density-functional theory (DFT) calculations of dimers adsorbed on metallic surfaces, and with a focus on the Dzyaloshinskii-Moriya interaction (DMI) which is essential for stabilizing chiral non-collinear magnetic states, we discuss the interpretation of the DMI when decomposed into microscopic electron and spin densities and currents. We clarify the distinct origins of spin currents induced in the system and their connection to the DMI. In addition, we reveal how non-collinearity affects the usual DMI, which is solely induced by spin-orbit coupling, and DMI-like interactions brought about by non-collinearity. We explain how the dependence of the DMI on the magnetic configuration establishes a connection between high-order magnetic interactions, enabling the transition from a local to a global spin Hamiltonian.},
keywords = {},
pubstate = {published},
tppubtype = {workingpaper}
}
A spin Hamiltonian, which characterizes interatomic interactions between spin moments, is highly valuable in predicting and comprehending the magnetic properties of materials. A deeper understanding of the microscopic origin of magnetic interactions can open new pathways toward realizing nanometer-scale systems for future spintronic devices. Here, we explore a method for explicitly calculating interatomic exchange interactions in non-collinear configurations of magnetic materials considering only a bilinear spin Hamiltonian in a local scenario. Based on density-functional theory (DFT) calculations of dimers adsorbed on metallic surfaces, and with a focus on the Dzyaloshinskii-Moriya interaction (DMI) which is essential for stabilizing chiral non-collinear magnetic states, we discuss the interpretation of the DMI when decomposed into microscopic electron and spin densities and currents. We clarify the distinct origins of spin currents induced in the system and their connection to the DMI. In addition, we reveal how non-collinearity affects the usual DMI, which is solely induced by spin-orbit coupling, and DMI-like interactions brought about by non-collinearity. We explain how the dependence of the DMI on the magnetic configuration establishes a connection between high-order magnetic interactions, enabling the transition from a local to a global spin Hamiltonian.