scholarly journals Difference between Brownian and Néel relaxation mechanisms in a magnetizing field

2021 ◽  
pp. 14-20
Author(s):  
Alexander V. Lebedev ◽  
Keyword(s):  
Relaxation Time ◽  
Oleic Acid ◽  
High Frequency ◽  
Cobalt Ferrite ◽  
Magnetic Moments ◽  
Relaxation Mechanism ◽  
Dynamic Susceptibility ◽  
Magnetite Particles ◽  
Magnetizing Field ◽  
Néel Relaxation

Measurements of the dynamic susceptibility of a magnetic fluid based on cobalt ferrite particles stabilized in water by a double surfactant layer have been carried out. Cobalt ferrite, in comparison with magnetite, has a significantly higher energy of magnetic anisotropy. Therefore, for particles of cobalt ferrite, the Brownian mechanism of relaxation of magnetic moments is characteristic. The Debye (with a finite relaxation time) contribution to the dynamic susceptibility and the high-frequency (dispersionless) contribution are distinguished by constructing Cole-Cole diagrams. It was found that with an increase in the magnetizing field, the Debye contribution to the dynamic susceptibility decreases, while the high-frequency one (having a zero relaxation time) remains unchanged. The indicated property of the dynamic susceptibility of a fluid with a Brownian relaxation mechanism is radically different from the properties of the susceptibility of a fluid with Néel particles. Previously, measurements were made of the susceptibility of a fluid based on magnetite particles stabilized with oleic acid in kerosene. The magnetite particles have significantly lower anisotropy energy and are characterized by the predominance of the Néel relaxation mechanism. Turning on the magnetizing field caused a decrease in both the Debye part of the susceptibility and the high-frequency part of the susceptibility of magnetite particles.

scholarly journals Thermal Traits of MNPs under High-Frequency Magnetic Fields: Disentangling the Effect of Size and Coating

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 797
Author(s):  
David Aurélio ◽  
Jiří Mikšátko ◽  
Miroslav Veverka ◽  
Magdalena Michlová ◽  
Martin Kalbáč ◽  
...  
Keyword(s):  
Oleic Acid ◽  
High Frequency ◽  
Cobalt Ferrite ◽  
Specific Power ◽  
Undecanoic Acid ◽  
Temperature Dependent ◽  
Frequency Magnetic Field ◽  
High Frequency Magnetic Field ◽  
Ethanol System ◽  
The Impact

We investigated the heating abilities of magnetic nanoparticles (MNPs) in a high-frequency magnetic field (MF) as a function of surface coating and size. The cobalt ferrite MNPs were obtained by a hydrothermal method in a water–oleic acid–ethanol system, yielding MNPs with mean diameter of about 5 nm, functionalized with the oleic acid. By applying another cycle of hydrothermal synthesis, we obtained MNPs with about one nm larger diameter. In the next step, the oleic acid was exchanged for 11-maleimidoundecanoic acid or 11-(furfurylureido)undecanoic acid. For the heating experiments, all samples were dispersed in the same solvent (dichloroethane) in the same concentration and the heating performance was studied in a broad interval of MF frequencies (346–782 kHz). The obtained results enabled us to disentangle the impact of the hydrodynamic, structural, and magnetic parameters on the overall heating capabilities. We also demonstrated that the specific power absorption does not show a monotonous trend within the series in the investigated interval of temperatures, pointing to temperature-dependent competition of the Brownian and Néel contributions in heat release.

Correlating Blocking Temperatures in Single Molecule Magnets with Raman Relaxation

2018 ◽  
Author(s):  
Marcus J. Giansiracusa ◽  
Andreas Kostopoulos ◽  
George F. S. Whitehead ◽  
David Collison ◽  
Floriana Tuna ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Single Molecule ◽  
Energy Barrier ◽  
Thermal Relaxation ◽  
Relaxation Mechanism ◽  
Blocking Temperature ◽  
Single Molecule Magnets ◽  
Single Molecule Magnet ◽  
Key Parameter

We report a six coordinate DyIII single-molecule magnet<br>(SMM) with an energy barrier of 1110 K for thermal relaxation of<br>magnetization. The sample shows no retention of magnetization<br>even at 2 K and this led us to find a good correlation between the<br>blocking temperature and the Raman relaxation regime for SMMs.<br>The key parameter is the relaxation time (𝜏<sub>switch</sub>) at the point where<br>the Raman relaxation mechanism becomes more important than<br>Orbach.

THE EFFECT OF HIGH FREQUENCY VENTILATION ON THE / PATTERN IN DOGS WITH OLEIC ACID LUNG DAMAGE

1982 ◽  
Vol 57 (3) ◽  
pp. A89-A89
Author(s):  
E. L. Owens ◽  
T. S. Lee ◽  
B. D. Wright ◽  
S. Jakobson
Keyword(s):  
Oleic Acid ◽  
High Frequency ◽  
Lung Damage ◽  
High Frequency Ventilation ◽  
Frequency Ventilation

scholarly journals The Effect of Particle Concentration on the Heating Rate of Ferrofluids for Magnetic Hyperthermia

2015 ◽  
Vol 58 (1) ◽  
pp. 81-88 ◽  
Author(s):  
I. Malaescu ◽  
C. N. Marin ◽  
M. Bunoiu ◽  
P. C. Fannin ◽  
N. Stefu ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Oleic Acid ◽  
Dilution Rate ◽  
Heating Rate ◽  
Particle Concentration ◽  
Magnetic Hyperthermia ◽  
Initial Sample ◽  
Frequency Field ◽  
Three Samples ◽  
Magnetite Particles

Abstract The complex magnetic susceptibility χ(f) = χ′(f) - i χ″(f), of a ferrofluid sample with magnetite particles dispersed in kerosene and stabilized with oleic acid, over the range 0.1 GHz to 6 GHz, was determined. The initial sample has been successively diluted with kerosene (with a dilution rate of 2/3), thus obtaining further three samples. Using the complex magnetic susceptibility measurements of each sample, the frequency field and particle concentration dependencies of the heating rate of the ferrofluid samples, were analyzed. The results show the possibility of using the heating rate of ferrofluid samples with different particle concentrations, in hyperthermia applications.

scholarly journals Multiscale Post-Seismic Deformation Based on cGNSS Time Series Following the 2015 Lefkas (W. Greece) Mw6.5 Earthquake

2021 ◽  
Vol 11 (11) ◽  
pp. 4817
Author(s):  
Filippos Vallianatos ◽  
Vassilis Sakkas
Keyword(s):  
Time Series ◽  
Relaxation Time ◽  
Relaxation Times ◽  
Relaxation Mechanism ◽  
Mesoscopic Scale ◽  
Macroscopic Scale ◽  
Epicentral Area ◽  
Arrhenius Dependence ◽  
Seismic Deformation ◽  
Logarithmic Type

In the present work, a multiscale post-seismic relaxation mechanism, based on the existence of a distribution in relaxation time, is presented. Assuming an Arrhenius dependence of the relaxation time with uniform distributed activation energy in a mesoscopic scale, a generic logarithmic-type relaxation in a macroscopic scale results. The model was applied in the case of the strong 2015 Lefkas Mw6.5 (W. Greece) earthquake, where continuous GNSS (cGNSS) time series were recorded in a station located in the near vicinity of the epicentral area. The application of the present approach to the Lefkas event fits the observed displacements implied by a distribution of relaxation times in the range τmin ≈3.5 days to τmax ≈350 days.

Hypersonic Velocity, Absorption and Relaxation in Molten CSNO3

1977 ◽  
Vol 32 (1) ◽  
pp. 57-60 ◽  
Author(s):  
H. E. Gunilla Knape ◽  
Lena M. Torell
Keyword(s):  
Relaxation Time ◽  
High Frequency ◽  
Viscosity Coefficient ◽  
Sound Waves ◽  
Frequency Range ◽  
Ultrasonic Velocities ◽  
Hypersonic Velocity ◽  
Frequency Shifts ◽  
Bulk Viscosity Coefficient ◽  
Good Agreement

Abstract Brillouin spectra of molten CSNO3 were investigated for scattering angles between 40 and 140° and in a temperature interval of 420-520 °C. An Ar+ singlemode laser was used for excitation and the total instrumental width was ~265 MHz. The measured frequency shifts and linewidths of the Brillouin components were used to determine velocities and attenuations of thermal sound waves in the frequency range 2.3-7.0 GHz. A dispersion of 4-5% was found between the present hyper­ sonic velocities and reported ultrasonic velocities. A considerable decrease in attenuation with frequency was observed in the investigated frequency range, with the value at high frequency ap­ proaching the classical attenuation. The results are in good agreement with Mountain's theory of a single relaxation time. The relaxation time of the bulk viscosity coefficient was calculated to 1.2×10-10S.

Regarding the Néel relaxation time constant in magnetorelaxometry

2014 ◽  
Vol 116 (16) ◽  
pp. 163914 ◽  
Author(s):  
J. Leliaert ◽  
A. Coene ◽  
G. Crevecoeur ◽  
A. Vansteenkiste ◽  
D. Eberbeck ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Relaxation Time Constant ◽  
Néel Relaxation

Dielectric relaxation of some aliphatic ketones in dilute solutions

1976 ◽  
Vol 54 (7) ◽  
pp. 794-799 ◽  
Author(s):  
M. P. Madan
Keyword(s):  
Free Energy ◽  
Relaxation Time ◽  
Dielectric Relaxation ◽  
Relaxation Mechanism ◽  
Relaxation Data ◽  
Nonpolar Solvents ◽  
Aliphatic Ketones ◽  
Entropy Of Activation ◽  
Enthalpy And Entropy ◽  
Dielectric Relaxation Behavior

The dielectric relaxation behavior of 2-butanone, 2-pentanone, 2-heptanone, and 3-nonanone in dilute nonpolar solvents, n-heptane, cyclohexane, benzene, and carbon tetrachloride has been studied in the microwave region at a number of temperatures. The relaxation data have been used to estimate the free energy, enthalpy, and entropy of activation for the relaxation mechanism. The values of the relaxation time for those solutions for which there are available known data agree well with other determinations. The results have been discussed in terms of dipole reorientation by intramolecular and overall molecular rotation and compared, wherever possible, with other similar studies on aliphatic molecules.

Sign in / Sign up

Export Citation Format

Share Document