arXiv subjects

R. Laskowski

Publications and source records attributed to R. Laskowski.

4 recordsLinked to original sources

arXiv2021

Angular dependence of hump-shape Hall Effects for distinguishing between Karplus-Luttinger and Geometrical Origins

Among the vast magnetic heterostructures explored in Condensed Matter Physics, two contrasting interpretations of the hump-shaped Hall Effects remain ambiguous and debated, namely, the overlap of two opposite-signed Karplus-Luttinger Hall loops associated with inhomogeneous collinear domains with perpendicular anisotropy, or the Geometrical/Topological Hall Effect emanated from hexagnal close-packed lattice of Skyrmion ground state with smoothly varying non-collinear moments. Their similarity in topology implies difficulty in discrimination via magnetic imaging. Here, this ambiguity is overcome and clarified by the divergence exponent of hump peak fields extracted from Hall measurements with magnetic field rotation on several heterostructures. Their difference in sensitivity to in-plane fields reveals that the former mechanism involves higher uniaxial anisotropy than the latter, departing from the Skyrmion ground state regime by the Ginzburg-Landau framework of triple-q spin-wave superposition. Numerous material systems can be summarized into a single curve of divergence exponent versus the collinear quality factor, bridging the crossover of the two mentioned mechanisms.

cond-mat.str-el↗

arXiv2020

Tailoring Magnetism in Self-intercalated Cr1+{\delta}Te2 Epitaxial Films

Magnetic transition metal dichalcogenide (TMD) films have recently emerged as promising candidates to host novel magnetic phases relevant to next-generation spintronic devices. However, systematic control of the magnetization orientation, or anisotropy, and its thermal stability, characterized by Curie temperature (Tc) remains to be achieved in such films. Here we present self-intercalated epitaxial Cr1+{\delta}Te2 films as a platform for achieving systematic/smooth magnetic tailoring in TMD films. Using a molecular beam epitaxy (MBE) based technique, we have realized epitaxial Cr1+{\delta}Te2 films with smoothly tunable over a wide range (0.33-0.82), while maintaining NiAs-type crystal structure. With increasing {\delta}, we found monotonic enhancement of Tc from 160 to 350 K, and the rotation of magnetic anisotropy from out-of-plane to in-plane easy axis configuration for fixed film thickness. Contributions from conventional dipolar and orbital moment terms are insufficient to explain the observed evolution of magnetic behavior with {\delta}. Instead, ab initio calculations suggest that the emergence of antiferromagnetic interactions with {\delta}, and its interplay with conventional ferromagnetism, may play a key role in the observed trends. To our knowledge, this constitutes the first demonstration of tunable Tc and magnetic anisotropy across room temperature in TMD films, and paves the way for engineering novel magnetic phases for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2016

NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations

We present a benchmark of the density functional linear response calculation of NMR shieldings within the Gauge-Including Projector-Augmented-Wave method against all-electron Augmented-Plane-Wave$+$local-orbital and uncontracted Gaussian basis set results for NMR shieldings in molecular and solid state systems. In general, excellent agreement between the aforementioned methods is obtained. Scalar relativistic effects are shown to be quite large for nuclei in molecules in the deshielded limit. The small component makes up a substantial part of the relativistic corrections.

cond-mat.mtrl-sci↗

arXiv2015

Ab-initio perspective on the Mollwo-Ivey relation for F-centers in alkali halides

We revisit the well-known Mollwo-Ivey relation that describes the "universal" dependence of the absorption energies of F-type color centers on the lattice constant $a$ of the alkali-halide crystals, $E_{\mbox{abs}}\propto a^{-n}.$ We perform both state-of-the-art ab-initio Quantum Chemistry and post-DFT calculations of F-center absorption spectra. By "tuning" independently the lattice constant and the atomic species we show that the scaling of the lattice constant alone (keeping the elements fixed) would yield $n=2$ in agreement with the "particle-in-the-box" model. Keeping the lattice constant fixed and changing the atomic species enables us to quantify the ion-size effects which are shown to be responsible for the exponent $n \approx 1.8$.

cond-mat.mtrl-sci↗