arXiv subjects

Vladimir L. Safonov

Publications and source records attributed to Vladimir L. Safonov.

At least 19 recordsLinked to original sources

arXiv2025

Exploring Weak Turbulence of Phonon and Magnon Beams in Magneto-Acoustic Ultrathin Films

This study presents a simple theoretical model describing narrow envelope surface acoustic waves (phonons) and spin waves (magnons) in an ultrathin ferromagnetic film. Based on the general principles of weak wave turbulence, the model considers interactions between beams of an ideal phonon gas and a weakly non-ideal magnon gas, which represent magnetoacoustic oscillations in the system. Equations for the wave envelopes of phonons and magnons, along with their harmonics, are derived, incorporating nonlinear effects from three- and four-particle interactions. In the general non-resonant case, linear stationary envelope simulations are sufficient. These clarify the experimentally observed angular dependence of the transmitted acoustic signal with respect to the orientation of the magnetic field. The study highlights increased energy losses associated with enhanced magnetoacoustic coupling. Given the broad interdisciplinary interest in weak turbulence phenomena within condensed matter physics and nonlinear wave dynamics, our model offers significant predictive capabilities and greatly simplifies calculations of quasiparticle beam interactions.

cond-mat.other↗

arXiv2019

Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry

The NV center in diamond has proven to be a powerful tool for locally characterizing the magnetic response of microwave excited ferromagnets. To date, this has been limited by the requirement that the FMR excitation frequency be less than the NV spin resonance frequency. Here we report NV relaxometry based on a two-magnon Raman-like process, enabling detection of FMR at frequencies higher than the NV frequency. For high microwave drive powers, we observe an unexpected field-shift of the NV response relative to a simultaneous microwave absorption signal from a low damping ferrite film. We show that the field-shifted NV response is due to a second order Suhl instability. The instability creates a large population of non-equilibrium magnons which relax the NV spin, even when the uniform mode FMR frequency exceeds that of the NV spin resonance frequency, hence ruling out the possibility that the NV is relaxed by a single NV-resonant magnon. We argue that at high frequencies the NV response is due to a two-magnon relaxation process in which the difference frequency of two magnons matches the NV frequency, and at low frequencies we evaluate the lineshape of the one-magnon NV relaxometry response using spinwave instability theory.

cond-mat.mes-hall↗

arXiv2017

Magnon Condensation and Spin Superfluidity

We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium magnons which leads to a spin superfluidity, the coherent quantum transfer of magnetization in magnetic materials. These phenomena are beyond the classical Landau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon density for ferro- and antiferromagnets, bulk and thin films are estimated and discussed. The BEC should occur in the antiferromagnetic hematite at much lower excited magnon density compared to the ferromagnetic YIG.

cond-mat.quant-gas↗

arXiv2017

Cooperative parametric resonance of the spin one half system of the dense atomic gas

The cooperative resonance for a spin one half system interacting with dc and ac magnetic field is considered. This interaction in the system collective regime can result in parametic resonance and rapid excitation of the excited spin state of the dense atomic gas. The phenomenon is studied using the density matrix approach. We discuss the implementation of this effect and possible applications of the quantum amplification by superradiant emission of radiation.

quant-ph↗

arXiv2015

Nonlinear Radiation Damping of Nuclear Spin Waves and Magnetoelastic Waves in Antiferromagnets

Parallel pumping of nuclear spin waves in antiferromagnetic CsMnF3 at liquid helium temperatures and magnetoelastic waves in antiferromagnetic FeBO3 at liquid nitrogen temperature in a helical resonator was studied. It was found that the absorbed microwave power is approximately equal to the irradiated power from the sample and that the main restriction mechanism of absortption in both cases is defined by the nonlinear radiation damping predicted about two decades ago. We believe that the nonlinear radiation damping is a common feature of parallel pumping technique of all normal magnetic excitations and it can be detected by purposeful experiments.

cond-mat.mes-hall↗

arXiv2013

Hydrogen nanobubbles in a water solution of dietary supplement

Using gas chromatography, proton nuclear magnetic resonance and qualitative experiments, we demonstrate that a water solution of dissolved dietary supplement, creating negative redox potential, contains invisible hydrogen nano-bubbles, which remain in the solution for several hours.

physics.med-ph↗

arXiv2006

Hard Disk Drive as a Magnetomechanical Logic Device

We consider the conditions how two binary numbers can be superimposed on the same track with the use of different recording magnetic fields. As a result the average magnetization of longitudinal medium along the track can have three states: -M, 0 and +M. Possibility to perform logic operations with these states is considered. We demonstrate OR, AND, XOR and NOT operations and discuss a modification of a recording device.

cs.OH↗

arXiv2005

Fluctuation-dissipation considerations and damping models for ferromagnetic materials

The role of fluctuation-dissipation relations (theorems) for the magnetization dynamics with Landau-Lifshitz-Gilbert and Bloch-Bloembergen damping terms are discussed. We demonstrate that the use of the Callen-Welton fluctuation-dissipation theorem that was proven for Hamiltonian systems can give an inconsistent result for magnetic systems with dissipation.

cond-mat.stat-mech↗

arXiv2004

Microscopic mechanisms of magnetization reversal

Two principal scenarios of magnetization reversal are considered. In the first scenario all spins perform coherent motion and an excess of magnetic energy directly goes to a nonmagnetic thermal bath. A general dynamic equation is derived which includes a tensor damping term similar to the Bloch-Bloembergen form but the magnetization magnitude remains constant for any deviation from equilibrium. In the second reversal scenario, the absolute value of the averaged sample magnetization is decreased by a rapid excitation of nonlinear spin-wave resonances by uniform magnetization precession. We have developed an analytic k-space micromagnetic approach that describes this entire reversal process in an ultra-thin soft ferromagnetic film for up to 90^{o} deviation from equilibrium. Conditions for the occurrence of the two scenarios are discussed.

cond-mat.other↗

arXiv2002

Thermal stability of coupled ferromagnetic and superparamagnetic particles

We consider a single-domain ferromagnetic particle with uniaxial anisotropy coupled to a single-domain soft ferromagnetic particle (superparamagnetic particle). The problem of thermally agitated magnetization reversal in this case can be reduced to the random magnetization dynamics of the first particle with an effectively larger anisotropy field. The magnetic external field is also altered in a manner that depends on the sign of the coupling and can be either enhanced or suppressed.

cond-mat.mtrl-sci↗

arXiv2002

Nonlinear microscopic relaxation of uniform magnetization precession

Dynamic relaxation for nonlinear magnetization excitation is analyzed. For direct processes, such as magnon-electron scattering and two-magnon scattering, the relaxation rate is determined from the linear case simply by utilizing the magnetization oscillation frequency for nonlinear excitation. For an indirect process, such as slow-relaxing impurities, the analysis gives an additional relaxation term proportional to the excitation level. In all cases the effective magnetization damping is increased compared to Landau-Lifshitz-Gilbert damping.

cond-mat.mtrl-sci↗

arXiv2002

Reply on ``Fluctuation-dissipation considerations for phenomenological damping models for ferromagnetic thin films'' [N. Smith, J. Appl. Phys. \bf{92}, 3877 (2002)]

We show that the critique of our recent papers presented in the abovementioned paper (NS) appeals to an incorrect mathematical analogy between electrical circuits and linear magnetization dynamics, improperly uses classical concepts of normal modes and basic equations, gives inconsistent results and therefore comes to incorrect conclusions.

cond-mat.mtrl-sci↗

arXiv2002

Microscopic relaxation mechanisms and linear magnetization dynamics

Linear magnetization dynamics in the presense of a thermal bath is analyzed for two general classes of microscopic damping mechanisms. The resulting stochastic differential equations are always in the form of a damped harmonic oscillator driven by a thermal field. The damping term contains both the interaction mechanisms and the symmetry of the magnetic system. Back transformation from the oscillator coordinates to the magnetization variables results in a macroscopic tensor form of damping that reflects the system anisotropy. Scalar Landau-Lifshitz-Gilbert damping term is valid only for systems with axial symmetry. Analysis of FMR linewith measurements versus frequency, temperature, and film thickness in NiFe films shows good agreement with a combination of slow-relaxing impurity and magnon-electron confluence processes.

cond-mat.stat-mech↗

arXiv2002

Continuous Unitary Transformations

In the present time we observe a growing number of publications where the, so-called, flow equations are successfully used to diagonalize Hamiltonians by means of an appropriate unitary transformation. Here we discuss and compare the flow equations (FE) method (proposed in 1994) with the method of one step continuous unitary transformations (OS CUT) (proposed in 1982). It is shown that the FE method can be considered as a generalization of the OS CUT approach to the case of parameter dependent generator. The OS CUT method gives linear differential equations for the diagonalization procedure. In the FE method the system of differential equations is nonlinear. Finally we discuss the generalization of idea of continuous unitary transformations for the case of quantum equations of motion (Heisenberg picture and density matrix).

quant-ph↗

arXiv2001

Tensor form of magnetization damping

A tensor form of phenomenological damping is derived for small magnetization motions. This form reflects basic physical relaxation processes for a general uniformly magnetized particle or film. Scalar Landau-Lifshitz damping is found to occur only for two special cases of system symmetry.

cond-mat.stat-mech↗

arXiv2001

Non-uniform thermal magnetization noise in thin films: application to GMR heads

A general scheme is developed to analyze the effect of non-uniform thermal magnetization fluctuations in a thin film. The normal mode formalism is utilized to calculate random magnetization fluctuations. The magnetization noise is proportional to the temperature and inversely proportional to the film volume. The total noise power is the sum of normal mode spectral noises and mainly determined by spin-wave standing modes with an odd number of oscillations. The effect rapidly decreases with increasing mode number. An exact analytical calcutaion is presented for a two-cell model.

cond-mat.stat-mech↗

arXiv2001

Thermal magnetization fluctuations in thin films and a new physical form for magnetization damping

The effect of thermal fluctuations on a thin film magnetoresistive element has been calculated. The technique involves adding to the basic spin dynamics a general form of interaction with a thermal bath. For a general anisotropic magnetic system the resulting equation can be written as a Langevin equation for a harmonic oscillator. Our approach predicts two times smaller noise power at low frequencies than the conventional stochastic Landau-Lifshitz-Gilbert equation. It is shown that equivalent results can be obtained by introducing a tensor phenomenological damping term to the gyromagnetic dynamics driven by a thermal fluctuating field.

cond-mat.mtrl-sci↗

arXiv2001

A single mode realization of SU(1,1)

A single mode realization of SU(1,1) algebra is proposed. This realization makes it possible to reduce the problem of two nonlinear interacting oscillators to the problem of free moving particle.

quant-ph↗