A5082481506- Magnetic properties of thin films
- Theoretical and Computational Physics
- Magnetism in coordination complexes
- Physics of Superconductivity and Magnetism
- Quantum and electron transport phenomena
- Lanthanide and Transition Metal Complexes
- Electron Spin Resonance Studies
- Advanced NMR Techniques and Applications
- Spectroscopy and Quantum Chemical Studies
- Magnetic Properties and Applications
- Advanced Thermodynamics and Statistical Mechanics
- Mechanical and Optical Resonators
- Advanced Condensed Matter Physics
- Characterization and Applications of Magnetic Nanoparticles
- Organic and Molecular Conductors Research
- Quantum many-body systems
- Stochastic processes and statistical mechanics
- Quantum optics and atomic interactions
- nanoparticles nucleation surface interactions
- stochastic dynamics and bifurcation
- Nonlinear Dynamics and Pattern Formation
- Magnetic Properties and Synthesis of Ferrites
- Magnetic Properties of Alloys
- Magneto-Optical Properties and Applications
- Material Dynamics and Properties
Lehman College
2014-2024
City University of New York
2015-2024
Peter the Great St. Petersburg Polytechnic University
2023
Chinese Academy of Sciences
2018
Leibniz Institute for Solid State and Materials Research
2018
Institute of Physics
2018
Lanzhou University
2018
King Abdullah University of Science and Technology
2018
National Physical Laboratory
2018
Johannes Gutenberg University Mainz
2002-2006
A macroscopic equation of motion for the magnetization a ferromagnet at elevated temperatures should contain both transverse and longitudinal relaxation terms interpolate between Landau-Lifshitz low Bloch high temperatures. It is shown that classical model where spin-bath interactions are described by stochastic Langevin fields spin-spin treated within mean-field approximation (MFA), such ``Landau-Lifshitz-Bloch'' (LLB) can be derived exactly from Fokker-Planck equation, if external...
The dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn${}_{12}\mathrm{Ac}$$(S=10)$ is developed. observed slow dynamics the system described by master equations for populations spin levels. latter are obtained adiabatic elimination fast degrees freedom from density matrix equation with help perturbation developed earlier level splitting [D. A. Garanin, J. Phys. A 24, L61 (1991)]. There exists a temperature range...
We calculate the contribution of Néel surface anisotropy to effective magnetic nanoparticles spherical shape cut out a simple cubic lattice. The arises because deviations atomic magnetizations from collinearity and thus energy depends on orientation global magnetization. result is second order in anisotropy, scales with particle's volume, has symmetry preferred directions [+/- 1, +/-1 , +/-1].
In conventional micromagnetism magnetic domain configurations are calculated based on a continuum theory for the magnetization. This assumes that absolute magnetization value is constant in space and time. Dynamics usually described with Landau-Lifshitz-Gilbert (LLG) equation, stochastic variant of which includes finite temperatures. Using simulation techniques atomistic resolution we show this micromagnetic approach fails higher temperatures since find two effects cannot be terms LLG...
Although a century has passed since the celebrated Einstein - de Haas experiments, microscopic mechanisms leading to conversion of spin angular momentum mechanical in elastic solids not been fully understood. In this paper D. A. Garanin and E. M. Chudnovsky explore concept phonon recently suggested by L. Zhang Q. Niu, Physical Review Letters 112, 085503 (2014). They show how it enters problem relaxation atomic body explicitly demonstrate conservation total spin-phonon processes at level.
Magnetic skyrmions are topologically protected nanoscale spin textures exhibiting fascinating physical behaviors. Recent observations of room temperature in sputtered multilayer films an important step towards their use ultra-low power devices. Such practical applications prefer to be stable at zero magnetic fields and temperature. Here, we report the creation skyrmion lattices Pt/Co/Ta multilayers by a scanning local field using force microscopy tips. We also show that those newly created...
We have found a novel feature of the bistable large-spin model described by Hamiltonian $H{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}DS}_{z}^{2}{\ensuremath{-}H}_{x}{S}_{x}$. The crossover from thermal to quantum regime for escape rate can be either first $({H}_{x}<SD/2)$ or second $(SD/2<{H}_{x}<2\mathrm{SD})$ order, that is, sharp smooth, depending on strength transverse field. This prediction tested experimentally in molecular magnets like...
Magnetic nanoparticles with N\'eel surface anisotropy, different internal structures, arrangements, and elongation are modeled as many-spin systems. The results suggest that the energy of cut from cubic lattices can be represented by an effective one-spin potential containing uniaxial anisotropies. It is shown values signs corresponding constants depend strongly on particle's arrangement, structure, shape. Particles a simple lattice have opposite sign term, compared to particles...
Interaction of two skyrmions stabilized by the ferromagnetic exchange, Dzyaloshinskii-Moriya interaction (DMI), and external magnetic field has been studied numerically on a 2D lattice size large compared to separation, $d$, between skyrmions. We show that same chirality (determined symmetry crystal) repel. In accordance with earlier analytical results, their long-range pair falls out separation as $\exp(-d/δ_H)$, where $δ_H$ is screening length, independent DMI. The prefactor in this...
The integral relaxation time ${\mathrm{\ensuremath{\tau}}}_{\mathrm{int}}$ of thermoactivating noninteracting single-domain ferromagnetic particles is calculated analytically in the geometry with a magnetic field H applied parallel to easy axis. It shown that drastic deviation ${\mathrm{\ensuremath{\tau}}}_{\mathrm{int}}^{\mathrm{\ensuremath{-}}1}$ from lowest eigenvalue Fokker-Planck equation ${\mathrm{\ensuremath{\Lambda}}}_{1}$ at low temperatures, starting some critical value H,...
We show that dislocations should be the main source of spin tunneling in ${\mathrm{Mn}}_{12}$ crystals. Long range strains caused by produce broad distribution relaxation times has been seen many experiments. When external magnetic field is applied along $c$ axis crystal, local rotations anisotropy due to result effective transverse unfreezes odd resonances. Scaling law derived provides universal description for all
It is shown that the tunnelling splitting of energy levels easy-axis spin system in a small transverse magnetic field can be calculated perturbationally for arbitrary S. The results are exact, contrast to those obtained previously same limit by indirect and rather difficult methods.
The escape rate $\ensuremath{\Gamma}$ of the large-spin model described by Hamiltonian $\mathcal{H}=\ensuremath{-}{\mathrm{DS}}_{z}^{2}\ensuremath{-}{H}_{z}{S}_{z}\ensuremath{-}{H}_{x}{S}_{x}$ is investigated with help mapping onto a particle moving in double-well potential $U(x)$. transition-state method yields moderate-damping case as Boltzmann average quantum transition probabilities. We have shown that from classical to regimes lowering temperature first order $(d\ensuremath{\Gamma}/dT$...
We present numerical and analytical results for the swiching times of magnetic nanoparticles with uniaxial anisotropy at elevated temperatures, including vicinity T_c. The consideration is based in Landau-Lifshitz-Bloch equation that includes relaxation magnetization magnitude M. resulting switching are shorter than those following from naive Landau-Lifshitz due to (i) additional barrier lowering because reduction M (ii) critical divergence damping parameters.
We consider relaxation of a rigid spin cluster in an elastic medium the presence magnetic field. Universal simple expression for spin-phonon matrix elements due to local rotations lattice is derived. The equivalence frame and laboratory approaches established. For Hamiltonians with strong uniaxial anisotropy field dependence transition rates analytically calculated its universality demonstrated. role time reversal symmetry transitions has been elucidated. theory provides lower bound on...
Thermodynamic quantities and correlation functions (CF's) of the classical antiferromagnet on kagom\'e lattice are studied for exactly solvable infinite-component spin-vector model, $\stackrel{\ensuremath{\rightarrow}}{D}\ensuremath{\infty}.$ In this limit, critical coupling fluctuations dies out behavior simplifies, but effect would-be Goldstone modes preventing ordering at any nonzero temperature is properly accounted for. contrast to conventional two-dimensional magnets with continuous...
Comprehensive theory of quantum spin relaxation in Mn-12 acetate crystals is developed, that takes into account imperfections the crystal structure and based upon generalization Landau-Zener effect for incoherent tunneling from excited energy levels. It shown linear dislocations at plausible concentrations provide transverse anisotropy which main source Mn-12. Local rotations easy axis due to result a magnetic field generated by applied along c-axis crystal, explains presence odd resonances....
We show that the theory of spin-phonon processes in paramagnetic solids must take into account coherent generation phonons by magnetic centers. This effect should drastically enhance rates nanoscale paramagnets and crystals molecular nanomagnets.
Large thermal fluctuations can destroy skyrmions - tiny speckles of rotated magnetization in two-dimensional films. Yet at low temperatures are believed to be topologically stable, which makes them good candidates for data storage and processing. However, as the authors demonstrate here, even zero temperature a nanoscale skyrmion is not protected against quantum decay. The theory based on imaginary-time dynamics skyrmion. Due fact that smallest still formed by many atomic spins, its decay...
We show that crystals of molecular nanomagnets can exhibit giant magnetic relaxation due to the Dicke superradiance electromagnetic waves. Rigorous theory is presented combines with Landau-Zener effect.
The local time-dependent theory of Einstein--de Haas effect is developed. We begin with microscopic interactions and derive dynamical equations that couple elastic deformations internal twists due to spins. applied the description motion a magnetic cantilever caused by oscillation domain wall. Theoretical results are compared recent experiment on in microcantilever.
Classical escape rates of uniaxial spin systems are characterized by a prefactor differing from and much smaller than that the particle problem, since maximum energy is attained everywhere on line constant latitude: theta =const, 0 < or= phi or = 2 pi. If transverse field applied, saddle point formed, high, moderate, low damping regimes (similar to those for particles) appear. Here we present first analytical numerical study crossovers between other systems. It shown there one HD-Uniaxial...