arXiv subjects

Marjana Ležaić

Publications and source records attributed to Marjana Ležaić.

11 recordsLinked to original sources

arXiv2026

Polarization of photoluminescence by optically driven orbital reconstruction in magnetically ordered CrCl3

Control of magnetic order through optical manipulation of orbital states can be realized in a wide range of materials, including insulators. In the latter case, electrons are excited into different electronic states, whose character may be a complex result of spin-orbit-lattice coupling. Here, we use a combination of polarization-resolved photoluminescence spectroscopy and density functional theory calculations to study excited Cr3+ ions in bulk, insulating antiferromagnetic CrCl3. Our results demonstrate a temperature-dependent preferential polarization direction below ~17 K, which reorients in the presence of an applied in-plane magnetic field. Density functional theory calculations reveal a local distortion of the ligand field and the generation of out-of-plane spin and orbital moments, following Cr3+ ion excitation. These changes link the photoluminescence polarization to the magnetic state of CrCl3. Our findings provide insight into the excited-state electronic structure of Cr3+ ions and suggest that CrCl3 is a promising candidate for opto-orbitronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Tailoring the anomalous Hall effect of SrRuO$_3$ thin films by strain: a first principles study

Motivated by the recently observed unconventional Hall effect in ultra-thin films of ferromagnetic SrRuO$_3$ (SRO) we investigate the effect of strain-induced oxygen octahedral distortion in the electronic structure and anomalous Hall response of the SRO ultra-thin films by virtue of density functional theory calculations. Our findings reveal that the ferromagnetic SRO films grown on SrTiO$_3$ (in-plane strain of $-$0.47$\%$) have an orthorhombic (both tilting and rotation) distorted structure and with an increasing amount of substrate-induced compressive strain the octahedral tilting angle is found to be suppressed gradually, with SRO films grown on NdGaO$_3$ (in-plane strain of $-$1.7$\%$) stabilized in the tetragonal distorted structure (with zero tilting). Our Berry curvature calculations predict a positive value of the anomalous Hall conductivity of $+$76\,S/cm at $-$1.7$\%$ strain, whereas it is found to be negative ($-$156\,S/cm) at $-$0.47$\%$ strain. We attribute the found behavior of the anomalous Hall effect to the nodal point dynamics in the electronic structure arising in response to tailoring the oxygen octahedral distortion driven by the substrate-induced strain. We also calculate strain-mediated anomalous Hall conductivity as a function of reduced magnetization obtained by scaling down the magnitude of the exchange field inside Ru atoms finding good qualitative agreement with experimental observations, which indicates a strong impact of longitudinal thermal fluctuations of Ru spin moments on the anomalous Hall effect in this system.

cond-mat.mtrl-sci↗

arXiv2019

Unconventional Ferroelectric Switching via Local Domain Wall Motion in Multiferroic $ε$-Fe2O3 Films

Deterministic polarization reversal in ferroelectric and multiferroic films is critical for their exploitation in nanoelectronic devices. While ferroelectricity has been studied for nearly a century, major discrepancies in the reported values of coercive fields and saturation polarization persist in literature for many materials. This raises questions about the atomic-scale mechanisms behind polarization reversal. Unconventional ferroelectric switching in $ε$-Fe2O3 films, a material that combines ferrimagnetism and ferroelectricity at room temperature, is reported here. High-resolution in-situ scanning transmission electron microscopy (STEM) experiments and first-principles calculations demonstrate that polarization reversal in $ε$-Fe2O3 occurs around pre-existing domain walls only, triggering local domain wall motion in moderate electric fields of 250 - 500 kV/cm. Calculations indicate that the activation barrier for switching at domain walls is nearly a quarter of that corresponding to the most likely transition paths inside $ε$-Fe2O3 domains. Moreover, domain walls provide symmetry lowering, which is shown to be necessary for ferroelectric switching. Local polarization reversal in $ε$-Fe2O3 limits the macroscopic ferroelectric response and offers important hints on how to tailor ferroelectric properties by domain structure design in other relevant ferroelectric materials.

cond-mat.mtrl-sci↗

arXiv2013

Engineering quantum anomalous Hall phases with orbital and spin degrees of freedom

Combining tight-binding models and first principles calculations, we investigate the quantum anomalous Hall (QAH) effect induced by intrinsic spin-orbit coupling (SOC) in buckled honeycomb lattice with sp orbitals in an external exchange field. Detailed analysis reveals that nontrivial topological properties can arise utilizing not only spin but also orbital degrees of freedom in the strong SOC limit, when the bands acquire non-zero Chern numbers upon undergoing the so-called orbital purification. As a prototype of a buckled honeycomb lattice with strong SOC we choose the Bi(111) bilayer, analyzing its topological properties in detail. In particular, we show the emergence of several QAH phases upon spin exchange of the Chern numbers as a function of SOC strength and magnitude of the exchange field. Interestingly, we observe that in one of such phases, namely, in the quantum spin Chern insulator phase, the quantized charge and spin Hall conductivities co-exist. We consider the possibility of tuning the SOC strength in Bi bilayer via alloying with isoelectronic Sb, and speculate that exotic properties could be expected in such an alloyed system owing to the competition of the topological properties of its constituents. Finally, we demonstrate that 3d dopants can be used to induce a sizeable exchange field in Bi(111) bilayer, resulting in non-trivial Chern insulator properties.

cond-mat.mes-hall↗

arXiv2012

Ab initio phonon structure of h-YMnO3 in low-symmetry ferroelectric phase

We present a systematic first-principles study of the phonon spectrum of hexagonal YMnO3 in ferroelectric (multiferroic) phase. We investigated in detail the low-energy phonon modes, their dispersion, symmetry, as well as the infrared optical properties of the crystal and determined the phonon density of states.

cond-mat.mtrl-sci↗

arXiv2012

First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO3

We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M- and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R\bar{3}c structures, all with antiferrodistortive rotations of the octahedra, have significantly lower total energy than the prototype Pm\bar{3}m structure. We discuss the dynamical stability of these structures, and the influence of the antiferrodistortive structural distortions on the vibrational, optical, and magnetic properties of EuTiO3, in the context of recent unexplained experimental observations.

cond-mat.mtrl-sci↗

arXiv2011

The HSE hybrid functional within the FLAPW method and its application to GdN

We present an implementation of the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional within the full-potential linearized augmented-plane-wave (FLAPW) method. Pivotal to the HSE functional is the screened electron-electron interaction, which we separate into the bare Coulomb interaction and the remainder, a slowly varying function in real space. Both terms give rise to exchange potentials, which sum up to the screened nonlocal exchange potential of HSE. We evaluate the former with the help of an auxiliary basis, defined in such a way that the bare Coulomb matrix becomes sparse. The latter is computed in reciprocal space, exploiting its fast convergence behavior in reciprocal space. This approach is general and can be applied to a whole class of screened hybrid functionals. We obtain excellent agreement of band gaps and lattice constants for prototypical semiconductors and insulators with electronic-structure calculations using plane-wave or Gaussian basis sets. We apply the HSE hybrid functional to examine the ground-state properties of rocksalt GdN, which have been controversially discussed in literature. Our results indicate that there is a half-metal to insulator transition occurring between the theoretically optimized lattice constant at 0 K and the experimental lattice constant at room temperature. Overall, we attain good agreement with experimental data for band transitions, magnetic moments, and the Curie temperature.

cond-mat.mtrl-sci↗

arXiv2011

Ferromagnetic spin coupling of 2p-impurities in band insulators stabilized by intersite Coulomb interaction: Nitrogen-doped MgO

For a nitrogen dimer in insulating MgO, a ferromagnetic coupling between spin-polarized $2p$-holes is revealed by calculations based on the density functional theory amended by an on-site Coulomb interaction and corroborated by the Hubbard model. It is shown that the ferromagnetic coupling is facilitated by a T-shaped orbital arrangement of the $2p$-holes, which is in its turn controlled by an intersite Coulomb interaction due to the directionality of the $p$-orbitals. We thus conjecture that this interaction is an important ingredient of ferromagnetism in band insulators with $2p$ dopants.

cond-mat.mtrl-sci↗

arXiv2011

High-temperature multiferroicity and strong magnetocrystalline anisotropy in 3d-5d double perovskites

Using density functional calculations we explore the properties of as-yet-unsynthesized $3d - 5d$ ordered double perovskites ($A_2BB'$O$_6$) with highly polarizable Bi$^{3+}$ ions on the $A$ site. We find that the Bi$_2$NiReO$_6$ and Bi$_2$MnReO$_6$ compounds are insulating and exhibit a robust net magnetization that persists above room temperature. When the in-plane lattice vectors of the pseudocubic unit cell are constrained to be orthogonal (for example, by coherent heteroepitaxy), the ground states are ferroelectric with large polarization and a very large uniaxial magnetocrystalline anisotropy with easy axis along the ferroelectric polarization direction. Our results suggest a route to multiferroism and electrically controlled magnetization orientation at room temperature.

cond-mat.mtrl-sci↗

arXiv2010

Complex magnetic behavior and high spin polarization in Fe(3-x)Mn(x)Si alloys

Fe3Si is a ferromagnetic material with possible applications in magnetic tunnel junctions. When doped with Mn, the material shows a complex magnetic behavior, as suggested by older experiments. We employed the Korringa-Kohn-Rostoker (KKR) Green function method within density-functional theory (DFT) in order to study the alloy Fe(3-x)Mn(x)Si, with 0 < x < 1. Chemical disorder is described within the coherent potential approximation (CPA). In agreement with experiment, we find that the Mn atoms align ferromagnetically to the Fe atoms, and that the magnetization and Curie temperature drop with increasing Mn-concentration $x$. The calculated spin polarization P at the Fermi level varies strongly with x, from P=-0.3 at x=0 (ordered Fe3Si) through P=0 at x=0.28, to P=+1 for x>0.75; i.e., at high Mn concentrations the system is half-metallic. We discuss the origin of the trends of magnetic moments, exchange interactions, Curie temperature and the spin polarization.

cond-mat.mtrl-sci↗

arXiv2005

Scanning tunneling microscopy of surfaces of half-metals: an ab-initio study on NiMnSb(001)

We present a first-principles study of the unreconstructed (001) surfaces of the half-metallic ferromagnet NiMnSb. Both terminations (MnSb and Ni) are considered. We find that half-metallicity is lost at the surfaces. After a discussion of the geometric relaxations and the spin-polarized surface band structure, we focus on topography images which are expected to be found with spin-polarized scanning tunneling microscopy. For the MnSb-terminated surface we find that only the Sb atoms are visible, reflecting a geometric buckling caused by relaxations. For the Ni-terminated surface we find a strong contrast between the images of forward and reverse tip-sample-bias of 0.5 eV, as well as a stripe-like image for reverse bias. We interpret these findings in terms of highly directional surface states which are formed in the spin-down gap region.

cond-mat.mtrl-sci↗