Exchange bias at ferromagnet-antiferromagnet interfaces underpins magnetic memory, spintronic devices, and nanoscale electromagnetic technologies, yet its behaviour in complex nanoscale heterostructures remains poorly understood. Here we uncover how exchange bias emerges in functional multiphase metal-oxide nanoparticles by combining gas-phase synthesis, advanced magnetic characterisation, and first-principles-informed spin-dynamics simulations. Using Ni-Cr/NiO nanoparticles as a model system, we show that exchange bias is governed not simply by the presence of ferromagnetic and antiferromagnetic phases, but critically by their nanoscale spatial distribution and interfacial topology. At 10 K, significant negative exchange bias (0.8 kOe) and coercivity enhancement (1.4 kOe) was exhibited; both decreased due to either Cr-segregation (at low Cr content) or to Cr accumulation inside the core (at high Cr content). The resulting competition between magnetic phases produces a temperature-driven inversion from negative to positive exchange bias and a crossover from exchange-dominated to dipolar interactions. By linking density-functional-theory calculations directly to spin-dynamics simulations of nanoparticle ensembles, we establish a predictive framework for designing exchange-coupled nanomagnets capable of operating beyond the superparamagnetic limit.

Alloy nanoparticles (nanoalloys) exhibit tuneable physicochemical properties that depend sensitively on their atomic arrangement, making control over chemical ordering a central challenge in nanomaterials design. While most theoretical studies consider nanoalloys in vacuum, practical systems are typically supported, where strong cluster-substrate interactions can introduce significant lattice strain. Here, we investigate strain as a control parameter for chemical ordering in bimetallic nanoalloys using atomistic molecular dynamics and Monte Carlo simulations. By imposing controlled tensile and compressive strain through an implicit anchored interface, we systematically probe the response of NiPt nanoparticles with distinct structural motifs. For truncated octahedral particles, we find that chemical ordering and segregation behaviour remain remarkably robust even under large strains, indicating that intrinsic thermodynamic preferences dominate. In contrast, icosahedral nanoparticles exhibit pronounced strain-induced chemical redistribution, with a significant increase in surface Ni concentration under tensile strain. This behaviour is attributed to the combined effects of intrinsic geometric frustration and a high fraction of undercoordinated sites in icosahedral structures. Our results demonstrate that strain can selectively modulate chemical ordering in nanoalloys in a structure-dependent manner, establishing a general framework for understanding strain-induced chemical ordering in nanoalloys.

The present study investigates the mechanism by which the thermodynamically stable form of carbamazepine, CBZ(III), transforms to the trigonal polymorph, CBZ(II), during ball milling in the presence of palmitic acid. Crystal-structure and lattice-energy analyses were performed, and molecular dynamics (MD) simulations provided insight into crystal-surface and molecular-level phenomena underpinning the phase transformation. The PIXEL formalism and the all-atom Coulomb–London–Pauli method reproduced the experimentally observed stability order between CBZ(III) and CBZ(II). MD indicates limited miscibility between CBZ and palmitic acid—both at crystal surfaces and in the melt. The transformation proceeds via surface fluidization of CBZ(III) and hydrophobic-interaction–driven aggregation of CBZ around palmitic-acid alkyl chains. MD of palmitic-acid inclusion in CBZ(II) channels, together with pore analyses, suggests that stable inclusion would require lattice dilation. Trajectory inspection further shows frequent guest–wall repulsive contacts that can expel palmitic acid from the voids. Further work is warranted to test whether the transformation mechanism proposed for the polymorphic transformation of CBZ(III)→CBZ(II) generalizes to other mechanically induced solid-state transformations.

Foundation machine learning interatomic potentials (MLIPs) are increasingly being used as drop-in replacements for first-principles calculations, enabling simulations of materials at length and time scales that were previously inaccessible. However, due to lack of ground truth data, their accuracy on structural and dynamical observables in finite thermodynamic ensembles is yet to be established. Here, we introduce Dyna-Mat-v1.0, a benchmark dataset of condensed-phase first-principles molecular dynamics trajectories designed to test foundation MLIPs at realistic finite-temperature conditions. Using this dataset, we evaluate 15 foundation MLIPs across four model tiers by comparing both single-point energy and force errors on first-principles configurations and observables generated from MLIP-driven trajectories. We find that "on average" models with lower single-point force errors also yield lower errors for structural and dynamical observables. However, there are individual systems for which low force errors lead to qualitative failures in the predicted structure. Pressure remains poorly described across most models, pointing to limitations in the density functional theory stress labels available in current large-scale training datasets. Finally, we construct an accuracy-cost Pareto frontier to identify the best trade-offs for molecular dynamics with foundation MLIPs, finding that the latest generation of cross-trained models is close to Pareto-optimal according to the accuracy metrics considered here. Overall, Dyna-Mat-v1.0 shows that end-to-end finite-temperature validation is essential for quantifying the predictive behaviour of foundation MLIPs, and provides a simple, scalable route for assessing them beyond static and harmonic benchmarks relevant to materials design.

Structural transformations in gold clusters deposited on a graphite substrate induced by the focused electron beam of a scanning transmission electron microscope are investigated using the classical molecular dynamics (MD) approach. The particular case study concerns Au309 clusters softly deposited on few-layer graphite and exposed to a 300 keV electron beam. Two mechanisms of energy transfer to the cluster during the irradiation are considered: (i) through the relaxation of collective electronic excitations and (ii) through the momentum transfer by the energetic primary electrons. A relativistic MD approach implemented in the MBN Explorer software package is used to simulate the collisions of energetic primary electrons with cluster atoms and to evaluate the amount of energy transferred to the cluster for different collision geometries. Characteristic times for the occurrence of these energy deposition events are estimated for realistic experimental irradiation conditions. The MD simulations of the cluster dynamics after irradiation show that the cluster temperature decreases rapidly during the first few tens of picoseconds, and the cluster cools down to a temperature close to its initial temperature within several hundred picoseconds. This time period is comparable to the characteristic time between two successive energy transfer events induced by plasmon excitations in the deposited cluster. A large number of successive energy transfer events (on the order of similar to 103-104) during irradiation can cumulatively lead to substantial heating of the deposited cluster and induce its structural transformations.

Frank-Shockley partial dislocations, with lines parallel to the < 1010 > direction, were studied in wurtzite GaN using atomistic calculations, based on density functional theory, and high resolution scanning transmission electron microscopy. Two types of dislocations were considered, that is, mixed 55 degrees and 73 degrees, with core configurations in their vacancy and interstitial variants of both gallium or nitrogen polarity. The core configurations of the mixed 55 degrees dislocation have a structure with a 7-atom ring, involving both gallium and nitrogen dangling bonds, associated with shallow gap states. The core configurations of the mixed 73 degrees dislocation with gallium polarity have a 3/5-atom ring structure, whereas those with nitrogen polarity have a structure with a 6-atom ring. These core configurations were found to be associated with both shallow and deep gap states, where the latter are due to either Ga-Ga bonds or interacting nitrogen dangling bonds. It was demonstrated that a direct discrimination between vacancy and interstitial core variants of the same partial dislocation, in a high resolution transmission electron microscopy observation, is impossible along the m-direction, unless the sample is rotated by +/- 30 degrees around the < 0001 > axis. This rotation reveals the I1 basal stacking fault, enabling its location to be determined in relation to the extra half-plane associated with the c/2 component. It also allows the core variant of the partial dislocation to be determined. Knowledge of the core structures of the m-line Frank-Shockley partial dislocation allowed for the decryption of the dissociation of the a + c edge dislocation, observed by high-resolution scanning transmission electron microscopy, which is involved in the relaxation of strain at the technologically relevant InGaN/GaN interfaces.

In this study, the classic double-slit experiment, originally developed for light waves is successfully adapted, to investigate the behavior of phonons in crystalline silicon. Through molecular dynamics (MD) simulations, how phonons can exhibit wave-like interference patterns when passing through two slits in a silicon block is explored. The results indicate that phonon waves behave similarly to photons, with slit distinct interference patterns. By manipulating geometric parameters such as slit width, distance, and length, in fringe distances that align with Young's double slit formula is observed to change. Key findings include the observation of phonon interference and the sensitivity of fringe distances to geometric configurations. Although some discrepancies with theory arose due to noise in the MD simulations, these results underscore the complexity of simulating phonon behavior in nanostructures. This study demonstrates that phonon behavior at the nanoscale can mirror classical wave interference phenomena, paving the way for future work that includes conducting physical experiments for validation and ultimately aiming to engineer devices that harness phononic interference for innovative applications in thermal management, microelectronics, and quantum computing.

Effective thermal management of electronic devices encounters substantial challenges owing to the notable power densities involved. Here, we propose layered MoS2 phononic crystals (PnCs) that can effectively reduce thermal conductivity (κ) with relatively small disruption of electrical conductivity (σ), offering a potential thermal management solution for nanoelectronics. These layered PnCs exhibit remarkable efficiency in reducing κ, surpassing that of Si and SiC PnCs with similar periodicity by ~100-fold. Specifically, in suspended MoS2 PnCs, we measure an exceptionally low κ down to 0.1 watts per meter kelvin, below the amorphous limit while preserving the crystalline structure. These findings are supported by molecular dynamics simulations that account for the film thickness, porosity, and temperature. We demonstrate the approach efficiency by fabricating suspended heat-routing structures that effectively confine and guide heat flow in prespecified directions. This study underpins the immense potential of layered materials as directional heat spreaders, thermal insulators, and active components for thermoelectric devices.

Phonon diffraction and interference patterns are observed at the atomic scale, using molecular dynamics simulations in systems containing crystalline silicon and nanometric obstacles, such as voids or amorphous inclusions. The diffraction patterns due to these nano-architectured systems of the same scale as the phonon wavelengths are similar to the ones predicted by the simple Fresnel–Kirchhoff integral. The few differences between the two approaches are attributed to the nature of the interface and the anisotropy of crystalline silicon. Based on the wave description of phonons, these findings can provide insights into the interaction of phonons with nano-objects and can have applications in smart thermal energy management.

Herein, the stabilization of 2D single‐atom high gold rafts containing up to ≈60 Au atoms on amorphous carbon, fabricated by sputtering of atoms and imaged by aberration‐corrected scanning transmission electron microscopy, is demonstrated. These rafts deviate from the established cluster transition from 2D to 3D Au structural motifs in free clusters, which occurs in the region of 10–14 atoms. The experimental findings are supported by explicit ab initio calculations of Aun (n = 3–147) clusters on graphene and the role of cluster–surface interactions in the stabilization of the 2D single‐atom high Au cluster rafts on graphene is revealed. The transition from equilibrium 2D–3D structures is delayed to n = 19, while metastable 2D single‐atom high rafts compete with 3D structures up to about n = 60 atoms. The catalytic activity of supported nanoclusters depends strongly on their structure (and carbon‐based supports are used for a number of reactions); therefore these results are relevant to the catalytic performance of nanocluster‐based catalysts.

AbstractCombining ferromagnetic–antiferromagnetic materials in nanoalloys (i.e., nanoparticles, NPs, containing more than one element) can create a diverse landscape of potential electronic structures. As a result, a number of their magnetic properties can be manipulated, such as the exchange bias between NP core and shell, the Curie temperature of nanoparticulated samples, or their magnetocaloric effect. In this work, such a family of materials (namely M–Cr NPs where M is Fe, Co, Ni, or some combination of them) is reviewed with respect to the tunability of their magnetic properties via optimized doping with Cr up to its solubility limit. To this end, gas‐phase synthesis has proven a most effective method, allowing excellent control over the physical structure, composition, and chemical ordering of fabricated NPs by appropriately selecting various deposition parameters. Recent advances in this field (both experimental and computational) are distilled to provide a better understanding of the underlying physical laws and point toward new directions for cutting‐edge technological applications. For each property, a relevant potential application is associated, such as memory cells and recording heads, induced hyperthermia treatment, and magnetic cooling, respectively, aspiring to help connect the output of fundamental and applied research with current real‐world challenges.

The effect of point defects and interactions with thesubstrateare shown by density functional theory calculations to be of significantimportance for the structure and functional properties of hexagonalboron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG)and Ni(111) substrates. The structure, surface chemistry, and electronicproperties are calculated for h-BN systems with selected intrinsic,oxygen, and carbon defects and with graphene hybrid structures. Theelectronic structure of a pristine monolayer of h-BN is dependenton the type of substrate, as h-BN is decoupled electronically fromthe HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111)substrate, metallic-like behavior is predicted. These different film/substratesystems therefore show different reactivities and defect chemistries.The formation energies for substitutional defects are significantlylower than for intrinsic defects regardless of the substrate, andvacancies formed during film deposition are expected to be filledby either ambient oxygen or carbon from impurities. Significantlylower formation energies for intrinsic and oxygen and carbon substitutionaldefects were predicted for h-BN on Ni(111). In-plane h-BCN hybridstructures were predicted to be terminated by N-C bonding.Substitutional carbon on the boron site imposes n-type semiconductivityin h-BN, and the n-type character increases significantly for h-BNon HOPG. The h-BN film surface becomes electronically decoupled fromthe substrate when exceeding monolayer thickness, showing that thesurface electronic properties and point defect chemistry for multilayerh-BN films should be comparable to those of a freestanding h-BN layer.

Thin layers of ferromagnetic/non-magnetic bimetallic heterostructures have become the focal point of spintronics, primarily due to their capacity to convert spin to charge current, leveraging the spin- and inverse spin Hall effects. However, the interfacial properties and morphologies can significantly influence this conversion. Hence, we employed molecular dynamics calculations to model the construction of the Fe/Pt interface at various bilayer growth temperatures and Pt deposition rates. We then experimentally evaluated the modeling using x-ray methods to resolve the chemical and structural state of the interface. The calculations revealed moderate diffusive phenomena between the adjacent layers and an interfacial roughness of less than 1 nm, consistent with the experimental observations. In cases where plastic relaxation of the Fe/Pt interface is insufficient, lattice deformation is mitigated by a local pseudomorphic growth caused by transformation of the Pt crystal symmetry. Additionally, interfacial planar defects may emerge as a complementary stress-relieving mechanism to misfit dislocations. By combining the experimental and computational findings, we propose optimized growth conditions for an "ideal" Fe/Pt interface, which could serve as a useful tool to control the efficiency of spin-to-charge conversion.

The elucidation of the residual and intentional doping processes in ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is a major but still largely unexplored issue despite its primary importance for many nanoscale engineering devices. Here, we investigate the local structural environment around Ga dopants in ZnO NWs by combining synchrotron radiation-based x-ray linear dichroism with density functional theory calculations. We show that the family of VZn-GaZn-nH defect complexes is predominantly formed and hence that hydrogen acts as an efficient passivating species even for intentional dopants like Ga. The residual and intentional doping processes are found to be highly correlated through significant interplay effects. These findings revisit the nature of intentional dopant-induced defects and defect complexes in ZnO NWs. They further reveal that hydrogen should be considered in unintentionally doped ZnO NWs grown by CBD as major defects but also in intentionally doped ZnO NWs through its efficient passivating effect, opening perspectives to more finely control their optical and electrical properties.

SmCo5 is a well-established material in the permanent magnet industry, a sector which constantly gains market share due to increasing demand but also suffers from criticality of some raw materials. In this work we study the possibility of replacement of Sm with other, more abundant rare earth atoms like Ce-La. These raw materials are usually called “free” rare-earth minerals, appearing as a by-product during mining and processing of other raw materials. Samples with nominal stoichiometry Sm1−xMMxCo5 (x = 0.1–1.0) were prepared in bulk form with conventional metallurgy techniques and their basic structural and magnetic properties were examined. The materials retain the hexagonal CaCu5-type structure while minor fluctuations in unit cell parameters as observed with X-ray diffraction. Incorporation of Ce-La degrade intrinsic magnetic properties, Curie temperature drops from 920 K to 800 K across the series and mass magnetization from 98 Am2/kg to 60 Am2/kg; effects which trade off for the significantly reduced price. Atomistic simulations, implemented based on Density Functional Theory calculations are used in the case of the stoichiometry with x = 0.5 to calculate atomic magnetic moments and provide additional insight in the complex interactions that dominate the magnetic properties of the material.

A high-throughput benchmarking technique for testing the performance of different exchange-correlation functionals and pseudopotentials is proposed and applied to bulk SnS. It is shown that, contrary to the popular view that the local density approximation can best describe layered materials, a semilocal pseudopotential with a functional having a gradient dependence better described lattice vectors and `tetragonicity' of the lattice. We classify the pseudopotentials based on this value and show that the participation ratio of maximally localized Wannier functions follows the theory which states that more distorted structures have higher anti-bonding hybridization as stabilizing factor. In order to classify pseudopotentials, the local and nonlocal potential contributions to the dynamical Born effective charges are taken for each pseudopotential. Finally, a strategy is proposed for learning exchange-correlation functionals based on the distinction between short and long range parts of the Kohn-Sham potential.

In modern electrical circuits overheating is an issue and techniques enabling efficient heat dissipation are critical. One potential solution to dissipate excess heat away from critical electronic components are 2D materials, due to their high thermal anisotropy and possibility of directing the heat flow. Here, we propose heat routing structures based on few-layer, nanopatterned MoS2 to confine and guide the heat flow in a pre-specified in-plane direction. In such structures heat can be evacuated away from hotspots through a predefined path without affecting adjacent structures, a functionality which is limited in the standard materials for heat spreading. Our designs result from experimental and theoretical study of the in-plane thermal conductivity (κ) as a function of thickness, porosity, and temperature in both pristine (κ) and nanopatterned (κp) MoS2 membranes. Reduction factors R (κ/κp) greater than 10 and 80 are obtained after nanopatterning a square lattice of ~100-nm diameter holes with periods of 500 and 300 nm, respectively. Notably, the R for nanopatterned MoS2 is 10 times larger than for materials such as silicon with a similar periodicity. These results highlight the potential use of MoS2 for thermal management applications as directional in-plane heat dissipators, for instance in three-dimensional integrated circuits.

Αtomistic simulations based on density functional theory were performed to investigate Shockley partial dislocations, parallel to the <11–20> direction, in wurtzite gallium nitride. The cores of both 30° and 90° Shockley partial dislocations, their possible reconstructions and their electronic structures were analyzed and compared systematically. Shockley partial dislocations were found to have a variety of core structures while exhibiting different bonding states like: deformed Ga–N bonds, Ga–Ga and N–N homo-nuclear bonds, as well as Ga– and N–dangling bonds. We have demonstrated that the core reconstruction of these dislocations is not always energetically favourable in wurtzite GaN, as it is the case in elemental semiconductors. It results from interplay between the energy gain from eliminating dangling and forming homo-nuclear bonds and the energy excess from the induced strain of hetero-nuclear Ga–N bonds within the core. Depending on their core configurations, Shockley partial dislocations are expected to have different electronic behaviours in wurtzite GaN, as they can act either as sources of parasitic luminescence or non-radiative recombination centres, or give pathways to leakage currents. We have demonstrated that deep states associated with dislocations are not due to the dangling bonds, as generally believed, but rather to Ga–Ga bonds in their cores, and that N–N bonds do not lead to any gap states. These results are of high relevance as guidelines in defect engineering strategies aiming at producing dislocations with a particular electronic behaviour in wurtzite GaN.

Among the properties that distinguish nanoparticles (NPs) from their bulk counterparts is their lower melting points. It is also common knowledge that relatively low melting points enhance the coalescence of (usually) nascent nanoclusters toward larger NPs. Finally, it is well established that the chemical ordering of bi- (or multi-) metallic NPs can have a profound effect on their physical and chemical properties, dictating their potential applications. With these three considerations in mind, we investigated the coalescence mechanisms for Ni and Pt NPs of various configurations using classical molecular dynamics (MD) computer simulations. Benchmarking the coalescence process, we identified a steeper melting point depression for Pt than for Ni, which indicates a reversal in the order of melting for same-size NPs of the two elements. This reversal, also evident in the nano-phase diagram thermodynamically constructed using the regular solution model, may be useful for utilising NP coalescence as a means to design and engineer non-equilibrium NPs via gas-phase synthesis. Indeed, our MD simulations revealed different coalescence mechanisms at play depending on the conditions, leading to segregated chemical orderings such as quasi-Janus core-satellite, or core-(partial) shell NPs, despite the expected theoretical tendency for elemental mixing.

ZnO nanowires (NWs) grown by chemical bath deposition (CBD) have received great interest for nanoscale engineering devices, but their formation in aqueous solution containing many impurities needs to be carefully addressed. In particular, the pH of the CBD solution and its effect on the formation mechanisms of ZnO NWs and of nitrogen- and hydrogen-related defects in their center are still unexplored. By adjusting its value in a low- and high-pH region, we show the latent evolution of the morphological and optical properties of ZnO NWs, as well as the modulated incorporation of nitrogen- and hydrogen-related defects in their center using Raman and cathodoluminescence spectroscopy. The increase in pH is related to the increase in the oxygen chemical potential (μO), for which the formation energy of hydrogen in bond-centered sites (HBC) and VZn-NO-H defect complexes is found to be unchanged, whereas the formation energy of zinc vacancy (VZn) and zinc vacancy-hydrogen (VZn-nH) complexes steadily decreases as shown from density-functional theory calculations. Revealing that these VZn-related defects are energetically favorable to form as μO is increased, ZnO NWs grown in the high-pH region are found to exhibit a higher density of VZn-nH defect complexes than ZnO NWs grown in the low-pH region. Annealing at 450 °C under an oxygen atmosphere helps tuning the optical properties of ZnO NWs by reducing the density of HBC and VZn-related defects, while activating the formation of VZn-NO-H defect complexes. These findings show the influence of pH on the nature of Zn(ii) species, the electrostatic interactions between these species and ZnO NW surfaces, and the formation energy of the involved defects. They emphasize the crucial role of the pH of the CBD solution and open new possibilities for simultaneously engineering the morphology of ZnO NWs and the formation of nitrogen- and hydrogen-related defects.