arXiv subjects

Grzegorz Kwiatkowski

Publications and source records attributed to Grzegorz Kwiatkowski.

8 recordsLinked to original sources

arXiv2025

Time Reversible Integration of the Landau-Lifshitz-Gilbert Equation

A method for time-reversible numerical integration of the deterministic Landau-Lifshitz Gilbert equation by means of a second order Suzuki-Trotter decomposition is presented and tested against commonly used second order predictor-corrector methods. We find the time-reversibility of the Suzuki-Trotter integrator to be superior by several orders of magnitude while the computational effort is similar. Calculations of trajectories backwards in time are useful, for example, when evaluating dynamical corrections to transition state theory.

physics.comp-ph↗

arXiv2024

The role of nuclear spin diffusion in dynamic nuclear polarization of crystalline nanoscale silicon particles

Hyperpolarized nanoparticles (NPs) offer high polarization levels with room temperature relaxation times exceeding half an hour. In this work, we demonstrate that the achievable hyperpolarization enhancement and relaxation (decay) time at room temperature are largely independent of the particle size contrary to previous assumptions. This is explained through first-principles spin-diffusion coefficient calculations and finite-element polarization simulations. The simulated zero-quantum (flip-flop) line width governing the spin diffusion is found to agree with the experimentally accessible single-quantum (single spin flip, e.g. radio-frequency pulse) line width. The transport of hyperpolarization from strongly hyperfine-coupled spins towards the bulk is most likelybelieved to be responsible for the slow polarization dynamics including long room temperature decay time. The line width and spin-diffusion simulations are extended to other cubic crystal structures and analytical expressions, which only require insertion of the gyromagnetic ratio, lattice constant, isotope abundance and measured spectral density distribution (nuclear line width), are fitted. The presented simulations can be adjusted to study spin diffusion in other materials.

quant-ph↗

arXiv2020

Toward room-temperature nanoscale skyrmions in ultrathin films

Breaking the dilemma between small size and room temperature stability is a necessary prerequisite for skyrmion-based information technology. Here we demonstrate by means of rate theory and an atomistic spin Hamiltonian that the stability of isolated skyrmions in ultrathin ferromagnetic films can be enhanced by the concerted variation of magnetic interactions while keeping the skyrmion size unchanged. We predict film systems where the lifetime of sub-10 nm skyrmions can reach years at ambient conditions. The long lifetime of such small skyrmions is due to exceptionally large Arrhenius pre-exponential and the stabilizing effect of the energy barrier is insignificant at room temperature. A dramatic increase in the pre-exponential is achieved thanks to softening of magnon modes of the skyrmion, thereby increasing the entropy of the skyrmion with respect to the transition state for collapse. Increasing the number of skyrmion deformation modes should be a guiding principle for the realization of nanoscale, room-temperature stable skyrmions.

cond-mat.mes-hall↗

arXiv2019

Effect of anisotropy distribution on local nucleation field in bistable ferromagntic microwires

Critical parameters defining the local nucleation field in amorphous ferromagnetic microwires with positive magnetostriction are obtained analytically through scaling procedures. Exact value of the nucleation field is obtained numerically as a function of geometric parameters of anisotropy distribution, which is fully taken into account instead of being averaged out. It is established that the value of nucleation field depends predominantly on the steepness of anisotropy change withing the boundary between axial and radial domains, while the maximal value of anisotropy inside the wire or an overall average is not relevant.

cond-mat.mtrl-sci↗

arXiv2017

Domain shape dependence of semiclassical corrections to energy

Stationary solution of one-dimensional Sine-Gordon system is embedded in a multidimensional theory with explicitly finite domain in the added spatial dimensions. Semiclassical corrections to energy are calculated for static kink solution with emphasis on the impact of scale of the domain as well as the choice of boundary conditions on the results for rectangular cross-section.

quant-ph↗

arXiv2012

Quantum corrections to phi^4 model solutions and applications to Heisenberg chain dynamics

The Heisenberg spin chain is considered in phi^4 model approximation. Quantum corrections to classical solutions of the one-dimensional phi^4 model within the correspondent physics are evaluated with account of rest $d-1$ dimensions of a d-dimensional theory. A quantization of the models is considered in terms of space-time functional integral. The generalized zeta-function formalism is used to renormalize and evaluate the functional integral and quantum corrections to energy in quasiclassical approximation. The results are applied to appropriate conditions of the spin chain models and its dynamics, which elementary solutions, energy and the quantum corrections are calculated.

math-ph↗

arXiv2011

Green function diagonal for a class of heat equations

A construction of the heat kernel diagonal is considered as element of generalized Zeta function, that, being meromorfic function, its gradient at the origin defines determinant of a differential operator in a technique for regularizing quadratic path integral. Some classes of explicit expression in the case of finite-gap potential coefficient of the heat equation are constructed.

math-ph↗

arXiv2011

On quantum corrections to dislocations mass

Quasi-classical quantization of crystal dislocations field is considered in terms of functional integral. The generalized zeta-function is used to evaluate the functional integral and quantum corrections to mass in quasi-classical approximation. The quantum corrections to few classical solutions of one-dimensional Sin-Gordon model are evaluated with account of rest $n-1$ dimensions. The results are applied to appropriate crystal dislocation models.

quant-ph↗