arXiv subjects

Diego López-Alcalá

Publications and source records attributed to Diego López-Alcalá.

14 recordsLinked to original sources

arXiv2026

Intrinsic (non)-Gilbert damping in magnetic insulators calculated from a minimal model and ab initio spin Hamiltonians

We present an analytically solvable minimal model for the relaxation of low-frequency magnons in magnetic insulators arising from magnon-phonon and magnon-magnon interactions. The model establishes a direct connection between microscopic relaxation processes and Gilbert damping, and reveals how magnon decay evolves from bulk systems to the monolayer limit. We find that magnon-phonon coupling produces Gilbert damping of comparable magnitude in three- and two-dimensional magnets, with qualitative differences between flexural phonons in free-standing monolayers and three-dimensional phonons in substrate-supported layers. By contrast, non-Gilbert damping due to four-magnon scattering is strongly enhanced in two dimensions, where it becomes independent of spin-orbit coupling. To benchmark the model against real materials, we introduce a numerical approach for computing magnon damping from ab initio-derived spin Hamiltonians. We demonstrate that the central conclusions of the model remain valid for magnons in bulk YIG and several van der Waals magnetic insulators: CrSBr, CrI3 and CrPS4.

cond-mat.mtrl-sci↗

arXiv2026

Switchable Altermagnetism in a Layered van der Waals Metal-Organic Framework Driven by Spin-Crossover

Dynamical control of altermagnetism is a key requirement for translating its unique spin-dependent functionalities into practical spintronic devices, yet effective switching mechanisms remain largely unexplored. Here, we open an unprecedented, versatile and programmable route based on spin-crossover to switch altermagnetism on demand in molecular materials. Using density functional calculations, we demonstrate an altermagnetic ground state in the layered van der Waals MOFs MnX$_2$(tdz)$_2$ (X = Cl, Br; tdz = thiadiazole), stabilized by anisotropic interlayer exchange interactions, which gives rise to a characteristic d-wave momentum-space spin splitting and an associated spin-splitter transport response. Our findings reveal that under hydrostatic pressure, a high-spin to low-spin transition reconfigures the Mn d-orbital occupation, thus modifying the magnetic exchange network, and stabilizing a different antiferromagnetic ground state whose symmetry suppresses the nonrelativistic spin splitting. Crucially, spin-crossover switches altermagnetism not by directly altering the electronic structure, but by changing the symmetry of the magnetic ground state. These results establish molecular spin-crossover altermagnets as a platform for externally reconfigurable spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Electrical Control of Altermagnetism in a Quasi-1D Magnet

Altermagnetism is a collinear magnetic state characterized by momentum-dependent spin splitting in fully compensated materials. While widely investigated in systems governed by three- or two-dimensional exchange interactions, its extension to quasi-one-dimensional magnets remains almost unexplored. Focusing on the experimentally established AgCrP$_2$S$_6$ van der Waals magnet, we demonstrate that antiferromagnetic chains embedded in a two-dimensional lattice provide a general route to altermagnetism. Combining first-principles calculations and spin-space-group analysis, we show that out-of-plane symmetry breaking can generate a nonrelativistic d-wave spin splitting. An external out-of-plane electric field validates this mechanism, where the induced splitting increases linearly with field strength and reverses sign with field direction. We rationalize such behaviour by constructing an effective tight-binding model, which links the altermagnetic response to anisotropic third-neighbor interchain hoppings. Additionally, we show that Janus substitution also induces a d-wave spin texture, while ferroelectric interfacing with CuInP$_2$S$_6$ enables polarization-controlled spin-split bands in a fully compensated ferrimagnetic state. Our results establish quasi-one-dimensional antiferromagnets as building blocks for altermagnetism.

cond-mat.mtrl-sci↗

arXiv2026

Twist-engineering of a robust Quantum Spin Hall phase in $β$-/flat bismuthene bilayer from first principles

Twist-engineering of topological phases in two-dimensional materials offers a powerful route to modulate electronic structure beyond conventional strain or chemical control. In particular, group 15 (pnictogens) monolayers such as bismuthene provide an ideal platform due to their strong intrinsic spin-orbit coupling (SOC) and robust topological character. Here, we investigate a previously unexplored heterostructure consisting of a $β$-bismuthene monolayer rotated by 30$^\circ$ on a planar bismuthene layer stabilized on a SiC(0001) substrate. Using first-principles calculations, we demonstrate that this specific rotational alignment induces a unique interlayer orbital hybridization which, combined with the strong SOC and the naturally broken inversion symmetry, gives rise to a pronounced Rashba spin-splitting, absent in the isolated monolayers. The topological nature of the system is confirmed through the calculation of the Z2 topological invariant and Spin Hall Conductivity (SHC), revealing a robust Quantum Spin Hall (QSH) phase with an enhanced topological response compared to the individual layers. Furthermore, we explore the chemical tunability of this system via Sb substitution, showing that the gradual reduction of SOC systematically narrows the band gap while preserving the non-trivial topology. Our results establish large-angle twisted group 15 heterostructures as a versatile platform for engineering spin-orbit-driven phenomena and advancing topological spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Emergent $d$-wave altermagnetism in orthogonally twisted bilayer CrPS$_4$

Twistronics is a powerful strategy to engineer novel quantum states by controlling the relative orientation between layered materials. Here, we demonstrate that an orthogonally twisted bilayer CrPS$_4$ shows $d$-wave altermagnetism driven purely by structural rotation. Symmetry analysis reveals that the twisted stacking breaks partial translational combined with time-reversal symmetry, leading to a fourfold rotation relation between opposite spin sublattices, enabling altermagnetism. First-principles calculations demonstrate a sizable non-relativistic spin splitting of up to 68 meV around the Fermi level. We further show that the altermagnetic state can be further stabilized through interlayer compression and modulation of the on-site Coulomb interaction. The resulting band structure exhibits pronounced spin-dependent anisotropy, enabling efficient spin to charge conversion reaching $\sim$50% near the Fermi level and sizable giant magnetoresistance. These results establish twisted CrPS$_4$ as a realistic platform for altermagnetism and highlights twistronics as a versatile route for advanced spintronics applications.

cond-mat.mtrl-sci↗

arXiv2026

One-Dimensional Materials Supported in Two-Dimensional van der Waals Metal-Organic Frameworks with Optical Anisotropy Switching via Twist-Engineering

Van der Waals (vdW) materials provide a platform to study and control the physical properties of low-dimensional materials. While strategies developed for two-dimensional (2D) crystals are not directly transferable to one-dimensional (1D) systems, we can benefit from them by creating layers formed by interconnected chains. Here, we develop a molecular strategy to illustrate this concept consisting of assembling 1D materials in 2D metal-organic frameworks (MOFs). Crystals of [FeX(pzX)(bpy)] (X = Cl, F; pz = pyrazole; bpy = bipyridine) consist of iron chains along the b-axis, crosslinked via bpy ligands along the a-axis to form 2D layers, stacked along the c-axis via vdW forces. This structural anisotropy manifests itself in highly-anisotropic optical properties, as demonstrated by optical measurements in the visible and terahertz ranges, results which are supported by DFT calculations. Chemical substitution enables the tuning of the optical properties, as exemplified by the photoluminescence of the Cl-derivative, which is quenched for the F-derivative. Thin-layers are obtained by mechanical exfoliation, and their optical properties are further tuned through the fabrication of orthogonally-twisted vdW heterostructures, enabling to effectively switch-off the optical anisotropy. Our work highlights the chemical flexibility of vdW layered MOFs as a platform for designing and manipulating 1D architectures.

cond-mat.mtrl-sci↗

arXiv2026

Altermagnetic Metal-Organic Frameworks

Altermagnetism has recently emerged as a new class of spin compensated magnetic materials that exhibit momentum dependent spin splitting despite having zero net magnetization. The origin of these electronic signatures lies in symmetry operations that connect opposite spin sublattices while allowing spin splitting in momentum space. While most candidate materials identified so far belong to inorganic crystals with fixed lattice symmetries, the realization of altermagnetism ultimately requires platforms in which magnetic symmetry can be deliberately engineered. In this Perspective, we discuss how metal-organic frameworks (MOFs) provide a unique chemical platform to address this challenge. We first place altermagnetism in the broader context of magnetic and electronically active metal-organic networks, highlighting how reticular chemistry enables precise control over lattice geometry, dimensionality and electronic structure. We then discuss how these features position framework materials as promising candidates for realizing altermagnetism and highlight the key challenges that must be addressed to translate theoretical proposals into experimentally accessible systems. Finally, we critically assess current experimental challenges and outline emerging directions for realizing and controlling altermagnetism in coordination framework materials, which emerge as a versatile and powerful platform for exploring new paradigms in spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Chemical Engineering of Altermagnetism in Two-Dimensional Metal-Organic Frameworks

Altermagnetism represents a novel class of collinear antiferromagnetism exhibiting non-relativistic spin splitting without net magnetization, driven by lattice symmetry rather than spin-orbit coupling (SOC). Here, we introduce a coordination-driven chemical strategy to realize altermagnetic (AM) spin splitting in two-dimensional (2D) planar tetracoordinated Cr-based metal-organic frameworks (MOFs). Using density functional theory (DFT) calculations, we demonstrate that replacing centrosymmetric pyrazine (pyz) ligands with non-centrosymmetric imidazole (imz) linkers in Cr-based MOFs reduces lattice symmetry, enabling g-wave AM spin splitting up to 65 meV. Furthermore, frontier molecular orbital engineering (FMOE) allows selective ligand spin polarization, inducing a shift to d-wave AM anisotropy in polycyclic ligand-based 2D MOFs with spin splitting up to 83.9 meV. Microscopic magnetic exchange interactions (J) analysis reveals that ligand-mediated interactions dominate over metal-metal coupling, stabilizing AM order in systems with radical ligands. Interestingly, we further confirm AM spin splitting in spin wave spectrum, where chiral magnon splitting is observed. Finally, we show that AM spin splitting gives rise to experimentally accessible charge to spin conversion, emerging as a linear response in d-wave and as a symmetry-allowed nonlinear effect in g-wave 2D AM MOFs. This work establishes coordination chemistry as a powerful and versatile route to symmetry control in 2D MOFs, enabling rational design of 2D molecular materials with tunable electronic and AM properties for next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Confinement-Induced One-Dimensional Magnetism in CrSBr Chains via Carbon Nanotube Encapsulation

Encapsulating low-dimensional magnetic materials within carbon nanotubes (CNTs) offers a compelling route to stabilize unconventional magnetic states and engineer quantum functionalities at the limit of miniaturization. In this work, we systematically investigate the structural, electronic, and magnetic properties of one-dimensional (1D) CrSBr chains encapsulated within CNTs using density functional theory (DFT) and spin dynamics simulations. We demonstrate the structural stability of CrSBr@CNT, where confinement and charge transfer cooperate to stabilize ferromagnetism in the 1D limit, which persists up to 50 K. These findings position CrSBr@CNT as a model platform for realizing 1D magnetism and establish CNT encapsulation as a powerful strategy for exploring emergent quantum spin phenomena and engineering nanoscale spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Controlling Magnetism in the 2D van der Waals Antiferromagnet CrPS$_4$ via Ion Intercalation

Two-dimensional van der Waals (vdW) magnetic materials are versatile platforms for tailoring electronic and magnetic properties, in which the insertion of chemical species into their interlayer gaps offers a powerful route to engineer magnetism. Here, we focus on the A-type antiferromagnetic semiconductor CrPS$_4$ (T$_N$ = 38 K) and investigate its electronic and magnetic properties upon intercalation of lithium (Li$^+$) and organic tetrabutylammonium (TBA$^+$) ions using first-principles calculations. Our results show that Li$^+$ incorporation induces a semiconductor-to-metal transition in CrPS$_4$ and selectively modifies its magnetic behaviour: switching from out-of-plane to in-plane antiferromagnetism, followed by an in-plane ferromagnetic ground state at higher intercalation levels. This is accompanied by a continuous increase of the ordering temperature, reaching a fivefold enhancement for Li$_{0.5}$CrPS$_4$. Similarly, TBA$^+$ intercalation expands the vdW gap, decoupling CrPS$_4$ layers and stabilising in-plane ferromagnetism with a T$_C$ above 100 K. Furthermore, it also modifies magnon propagation, leading to enhanced group velocities and a more isotropic magnon transport. This work highlights intercalation as a powerful and versatile approach for controlling magnetic behaviour and spin dynamics, paving the way for the design of tunable 2D layered magnetic materials for spintronic and magnonic applications.

cond-mat.mtrl-sci↗

arXiv2025

Tunable Itinerant Ferromagnetism in the Two-Dimensional FePd$_2$Te$_2$ Hosting 1D Spin Chains

One-dimensional (1D) magnetism offers unidirectional spin interactions that allow unique tunable properties and unconventional spin phenomena. However, it often suffers from poor stability, limiting practical applications. In this regard, integrating 1D magnetism into two-dimensional (2D) materials enables a promising route to stabilize these systems while preserving their anisotropic magnetic characteristics. Here, we focus on the 2D ferromagnet FePd$_2$Te$_2$ (T$_C$ = 183K), which hosts 1D spin chains and strong in-plane anisotropy. Our first-principles calculations reveal highly anisotropic magnetic exchange interactions, confirming its 1D ferromagnetic nature. We modulate this behavior by Co and Ni substitution and introduce two new members of this family, CoPd$_2$Te$_2$ -- a ferromagnet -- and NiPd$_2$Te$_2$. Our results unveil the microscopic mechanisms governing the behaviour of FePd$_2$Te$_2$ and CoPd$_2$Te$_2$. Furthermore, we also demonstrate that the variation of the chain length is key to modulate magnetism. Finally, we determine the magnon dispersion, showcasing a pronounced anisotropy that enables unidirectional magnon propagation.

cond-mat.mtrl-sci↗

arXiv2024

Magnetic proximity effect in biphenylene monolayer from first-principles

On-surface chemistry has emerged as a key technique for designing novel low-dimensional materials, enabling precise manipulation of their electronic and magnetic properties at the atomic scale. It also proves highly effective for the fabrication of heterostructures. Leveraging these benefits, herein, we perform a first principles study of the magnetic proximity effect (MPE) in a heterostructure formed by a monolayer of the two-dimensional carbon allotrope biphenylene network (BPN) deposited on the surface of the above-room-temperature ferrimagnet yttrium iron garnet (YIG). Our results reveal strong hybridization between BPN orbitals and YIG surface states, resulting in non-homogeneous electron transfer and robust MPE. The proposed methodology accurately describes YIG magnetic interactions, allowing us to study the tuning effects of BPN on the magnetic properties of the substrate for the first time. Additionally, we explore the impact of van der Waals (vdW) distance at the interface, finding enhanced spin splitting up to 30% under external pressure. These findings highlight a promising strategy for inducing spin polarization in BPN without chemical modifications, opening new possibilities for BPN-based spintronic devices through the creation of heterostructures with magnetic materials.

cond-mat.mes-hall↗

arXiv2024

Graphendofullerene: a novel molecular two-dimensional ferromagnet

Carbon chemistry has attracted a lot of attention by chemists, physicists and material scientists in the last decades. The recent discovery of graphullerene provides a promising platform for many applications due to its exceptional electronic properties and the possibility to host molecules or clusters inside the fullerene units. Herein, we introduce graphendofullerene, a novel molecular-based two-dimensional (2D) magnetic material formed by trimetallic nitrides clusters encapsulated on graphullerene. Through first-principles calculations, we demonstrate the successful incorporation of the molecules into the 2D network formed by C$_{80}$ fullerenes, which leads to a robust long-range ferromagnetic order with a Curie temperature (Tc) of 38 K. Additionally, we achieve a 45% increase in Tc by strain engineering. These findings open the way for a new family of molecular 2D magnets based on graphendofullerene for advanced technologies.

cond-mat.mtrl-sci↗

arXiv2024

On the origin of the above-room-temperature magnetism in the 2D van der Waals ferromagnet Fe$_3$GaTe$_2$

Recent advancements in 2D magnetic materials have attracted a growing interest driven by their unique properties and potential applications in spintronic devices. However, the scarcity of systems that exhibit magnetism at room-temperature has limited their practical implementation into functional devices. In this work we focus on the recently synthetised van der Waals (vdW) ferromagnet Fe$_3$GaTe$_2$, which exhibits above-room-temperature magnetism (T$_{\mathrm{c}}$ = 350-380 K) and strong perpendicular magnetic anisotropy. Through first-principles calculations, we examine the magnetic properties of Fe$_3$GaTe$_2$ and compare them with the widely known Fe$_3$GeTe$_2$ ferromagnet. Our calculations unveil the complex microscopic mechanisms governing their magnetic behaviour, emphasizing the pivotal role of the ferromagnetic in-plane exchange interactions in the stabilization of the elevated T$_{\mathrm{c}}$ in Fe$_3$GaTe$_2$. Additionally, we predict the stability, strong perpendicular anisotropy and high T$_{\mathrm{c}}$ of single-layer Fe$_3$GaTe$_2$. We also demonstrate the potential of strain engineering and electrostatic doping to modulate its magnetic exchange interactions and anisotropy. Our results incentivise the isolation of the monolayer and pave the way for the future optimization of Fe$_3$GaTe$_2$ in magnetic and spintronic nanodevices.

cond-mat.mtrl-sci↗