arXiv subjects

M. Zając

Publications and source records attributed to M. Zając.

4 recordsLinked to original sources

arXiv2026

Molecular Nitrogen Formation in Nitrogen-Implanted (100) $β-Ga_2O_3$ Revealed by Temperature-Dependent $N$ $K$-edge XANES

The realization of $p$-type doping in wide-band-gap oxide semiconductors remains a major challenge, particularly in $β-Ga_2O_3$ where nitrogen has long been considered a potential acceptor dopant but has consistently failed to produce hole conductivity. Here we investigate the microscopic configuration of implanted nitrogen in (100) $β-Ga_2O_3$ using temperature-dependent $N$ $K$-edge x-ray absorption spectroscopy. The spectra reveal a pronounced $π^*$ resonance characteristic of molecular nitrogen, which becomes increasingly dominant upon thermal annealing. First-principles calculations and multiple-scattering simulations reveal a pronounced tendency for nitrogen atoms to form $N-N$ bonded configurations in the $Ga_2O_3$ matrix, particularly in defect-rich environments created by ion implantation, reproducing the characteristic spectral features observed in the $N$ $K$-edge XANES spectra. Structural analysis further indicates that implantation induces a defect-rich near-surface layer with local $β$-to-$γ$-like structural motifs, highlighting the strongly nonequilibrium structural environment in which nitrogen incorporation occurs. Reported results show that implanted nitrogen preferentially forms molecular $N_2$-like configurations rather than substitutional acceptors. Our results provide a microscopic explanation for the long-standing failure of nitrogen acceptor doping in $β-Ga_2O_3$ and reveal dopant molecularization as a previously overlooked pathway for impurity incorporation under strongly nonequilibrium implantation conditions.

cond-mat.mtrl-sci↗

arXiv2024

Imprinting of Antiferromagnetic Vortex States in NiO-Fe Nanostructures

Magnetic vortices are topological spin structures frequently found in ferromagnets, yet novel to antiferromagnets. By combining experiment and theory, we demonstrate that in a nanostructured antiferromagnetic-ferromagnetic NiO(111)-Fe(110) bilayer, a magnetic vortex is naturally stabilized by magnetostatic interactions in the ferromagnet and is imprinted onto the adjacent antiferromagnet via interface exchange coupling. We use micromagnetic simulations to construct a corresponding phase diagram of the stability of the imprinted antiferromagnetic vortex state. Our in depth analysis reveals that the interplay between interface exchange coupling and the antiferromagnet magnetic anisotropy plays a crucial role in locally reorienting the Néel vector out-of-plane in the prototypical in-plane antiferromagnet NiO and thereby stabilizing the vortices in the antiferromagnet.

cond-mat.mes-hall↗

arXiv2022

Reviewing the Geometric Hamilton-Jacobi Theory concerning Jacobi and Leibniz identities

In this survey, we review the classical Hamilton Jacobi theory from a geometric point of view in different geometric backgrounds. We propose a Hamilton Jacobi equation for different geometric structures attending to one particular characterization: whether they fulfill the Jacobi and Leibniz identities simultaneously, or if at least they satisfy one of them. In this regard, we review the case of time dependent and dissipative physical systems as systems that fulfill the Jacobi identity but not the Leibnitz identity. Furthermore, we review the contact evolution Hamilton Jacobi theory as a split off the regular contact geometry, and that actually satisfies the Leibniz rule instead of Jacobi. Furthermore, we include a novel result, which is the Hamilton-Jacobi equation for conformal Hamiltonian vector fields as a generalization of the well known Hamilton Jacobi on a symplectic manifold, that is retrieved in the case of a zero conformal factor. The interest of a geometric Hamilton Jacobi equation is the primordial observation that if a Hamiltonian vector field can be projected into a configuration manifold by means of a 1-form dW, then the integral curves of the projected vector field can be transformed into integral curves of the Hamiltonian vector field provided that W is a solution of the Hamilton-Jacobi equation. Geometrically, the solution of the Hamilton Jacobi equation plays the role of a Lagrangian submanifold of a certain bundle. Exploiting these features in different geometric scenarios we propose a geometric theory for multiple physical systems depending on the fundamental identities that their dynamic satisfies. Different examples are pictured to reflect the results provided, being all of them new, except for one that is reassessment of a previously considered example.

math.DG↗

arXiv2015

Phonons in ultrathin oxide films - 2D to 3D transition in FeO on Pt(111)

The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (ML) were studied using the nuclear inelastic scattering (NIS) of synchrotron radiation. Distinct evolution of vibrational characteristics with thickness that is revealed in the phonon density of states (PDOS) witnesses a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low energy part of the PDOS followed a linear dependence in energy that is characteristic for 2-dimensional systems. This dependence gradually transforms with thickness to the bulk ~E-square relation. Density functional theory phonon calculations perfectly reproduced the measured 1 ML PDOS within a simple model of a pseudomorphic FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long range magnetic order and stabilization of an unusual structural phase.

cond-mat.mtrl-sci↗