arXiv subjects

N. A. Gusev

Publications and source records attributed to N. A. Gusev.

4 recordsLinked to original sources

arXiv2026

Degeneracy and trajectory control of spin eigenmodes excited by fs-optical pulses in a nearly compensated ferrimagnet

We investigate optically excited spin dynamics in a uniaxial ferrimagnet near the magnetization compensation point under a magnetic field applied along the magnetic anisotropy axis. Experiment and numerical modeling reveal an unusual regime where the frequencies of two spin eigenmodes approach each other and become highly field sensitive. The modes, corresponding to opposite rotations of the Neel vector, simultaneously reverse their handedness at a critical field where their frequencies become degenerate. At this point, the two-frequency precessional dynamics collapses into a linear oscillations directed along the inverse-Faraday-effect excitation induced by a single pump pulse. We further show that a double-pulse excitation scheme enables control of the spin trajectory. These results uncover an unconventional dynamical regime in ferrimagnets and establish new opportunities for manipulating spin motion in magnonic systems and devices.

cond-mat.mtrl-sci↗

arXiv2026

The prospects of nonthermal magnetization switching in near-compensated rare earth iron garnets

Ultrafast spin dynamics in a magnetically compensated rare earth iron garnet film driven by femtosecond optical pulses through the inverse Faraday effect is theoretically investigated. Numerical simulations based on the equations of motion for the Néel vector reveal the temporal evolution of the system and its trajectories in the effective potential landscape tuned by external field and temperature. The results demonstrate a clear threshold behavior: weak pulses induce only oscillations around the initial equilibrium state, while a stronger excitation results in a deterministic magnetization switching. The switching threshold is determined by the magnetic state of the sample on its phase diagramme as well as on the laser pulse helicity. This mechanism demonstrates a non-thermal and even non-absorptive pathway towards optomagnonic logic and memory devices.

cond-mat.mtrl-sci↗

arXiv2023

Unconventional spin dynamics in the non-collinear phase of a ferrimagnet

Ferrimagnets containing several partially compensated magnetic sublattices are considered the most promising materials for all-optical data storage and for ultrafast communications based on spin waves. There are two magnetic phases of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics in ferrimagnets has been studied mostly in the collinear state without paying much attention to the kind of the magnetic phase. Here we investigate laser induced ultrafast spin dynamics in a rare-earth iron garnet film in the noncollinear phase as well. We identify a crucial influence of the magnetic phase on the excited spin modes which allowed us to discover several prominent effects previously overlooked. In particular, the non-collinearity makes the quasi-antiferromagnetic mode sensitive to the external magnetic field and brings its frequency close to the frequency of the quasiferromagnetic mode. The latter maximizes near the magnetization compensation point and vanishes towards the collinear phase. Spectacularly, at the phase transition the quasiferromagnetic mode becomes soft and its amplitude significantly increases reaching 7°. This opens new opportunities for the ultrafast control of spins in ferrimagnets for nonthermal data storage and data processing.

cond-mat.mtrl-sci↗

arXiv2009

On Solutions to the Wave Equation on Non-globally Hyperbolic Manifold

We consider the Cauchy problem for the wave equation on a non-globally hyperbolic manifold of the special form (Minkowski plane with a handle) containing closed timelike curves (time machines). We prove that the classical solution of the Cauchy problem exists and is unique if and only if the initial data satisfy to some set of additional conditions.

math-ph↗