Numerical calculations of the entropy and magnetization of magnetic fluids with chain aggregates

Abu‐Aljarayesh, I.; Migdadi, Sh.

doi:10.1016/s0304-8853(98)00341-2

Cited by 5 publications

(6 citation statements)

References 19 publications

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“…reaches values >5 when the field increases towards its saturation value, the conditions for the formation of thermodynamically stable chains λ 1 and λ ξ (according to the statistic model suggested by Zubarev [29]), are not met, since parameter λ in our case is relatively low. Additionally, in [30] it was shown that at ε m = 0.01, for λ < 4 and ξ 5, no particle chains are formed; only for λ ∼ 6-8 is their formation influenced positively by an increase of the field. This means that even if particle clusters are formed at strong fields, they are not stable aggregates and they only have a short lifetime.…”

Section: Methodsmentioning

confidence: 99%

The effect of the external magnetic field on the thermal relaxation of magnetization in systems of aligned nanoparticles

Caizer

2005

J. Phys.: Condens. Matter

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The dynamics of magnetic relaxation in a system of isolated ferrimagnetic nanoparticles depends on the ratio between the magnetic relaxation time (τ ) and the measurement time (t m ), which is usually considered to be equal to the period (T H ) of the external alternating magnetic field (t m = T H ). When t m approaches τ (τ < t m ), the magnetic moments cannot relax completely, thus leading to a deviation from the superparamagnetic behaviour (SPM), and a magnetic remanence of the system when the deviation is large. An external magnetic field (H ) can significantly change the dynamics of the relaxation, especially when its amplitude (H m ) is high. This paper shows that there is a limit field (threshold field (H p )) that depends on the anisotropy field of the nanoparticle, its magnetic volume and on the temperature; beyond this field, the magnetic moments cannot pass the potential barrier and they remain blocked. It will be shown that under these conditions the measurement time can no longer be considered to be t m = T H , but is a measurement time t mH < T H that in addition to T H will also depend on H p and H m . When the amplitude of the alternating magnetic field is lower than the value of the threshold field (H m < H p ), the measurement time is reduced to the period of the magnetic field. The theory proposed for a system of aligned nanoparticles has been verified experimentally in the case of a ferrofluid-type system. The result obtained brings in important corrections for determining the magnetic volume of the nanoparticles or the magnetic anisotropy constant if the condition t m = t mH < T H is used when H m is high (H m > H p ), instead of t m = T H .

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Section: Methodsmentioning

confidence: 99%

The effect of the external magnetic field on the thermal relaxation of magnetization in systems of aligned nanoparticles

Caizer

2005

J. Phys.: Condens. Matter

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“…The magnetization is then formally the equilibrium magnetization of a polydisperse ideal paramagnetic gas where the chains are the fundamental constituents. The chain length distribution is, however, a function of the magnetic field and furthermore of φ and λ. Abu-Aljarayesh and Migdadi [118] investigate this theory further, calculating the entropy and some equilibrium magnetization curves.…”

Section: Magnetizationmentioning

confidence: 99%

“…Zubarev and Iskakova investigate an interacting variant [190,191] of their chain model that has already been used to calculate the equilibrium magnetization in [118,119,127] and…”

Section: A Dilute/dense Phase Transitionsmentioning

confidence: 99%

Magnetic properties of colloidal suspensions of interacting magnetic particles

2004

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We review equilibrium thermodynamic properties of systems of magnetic particles like ferrofluids in which dipolar interactions play an important role. The review is focussed on two subjects: (i) the magnetization with the initial magnetic susceptibility as a special case and (ii) the phase transition behavior. Here the condensation ("gas/liquid") transition in the subsystem of the suspended particles is treated as well as the isotropic/ferromagnetic transition to a state with spontaneously generated long-range magnetic order.

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“…The other is the chain model. In this model, the magnetization property of ferrofluids is calculated by including chain formation [8][9][10][11][12]. However, the construction of a complete statistical theory for ferrofluid systems with the magnetic dipole interaction of particles or field-induced particle aggregation is still far from conclusion.…”

Section: Introductionmentioning

confidence: 99%

Effect of aggregates on the magnetization property of ferrofluids: A model of gaslike compression

Huang

Liu

et al. 2007

Science and Technology of Advanced Materials

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The effect of field-induced aggregation of particles on the magnetization property of ferrofluids is investigated. From the viewpoint of energy, magnetizability of ferrofluids is more complicated than predicted by Langevin theory because the aggregation, i.e., the transition of ferrofluid microstructure, would consume the energy of the applied magnetic field. For calculating the effect of aggregates on the magnetization of ferrofluids, a model of gaslike compression (MGC) is proposed to simulate the evolution of the aggregate structure. In this model, the field-induced colloidal particles aggregating in ferrofluids is equivalent to the ''gas of the particles'' being compressed by the applied magnetic field. The entropy change of the ferrofluid microstructure is proportional to the particle volume fraction in fieldinduced aggregates f H . On the basis of the known behavior of ferrofluid magnetization and the aggregate structure determined from the present experiments, f H is obtained and found to depend on the aggregating characteristic parameter of ferrofluid particles g in addition to the particle volume fraction in ferrofluids f and the strength of applied magnetic field H. The effect of the nonmagnetic surface layer of ferrofluid particles is also studied. The theory of MGC conforms to our experimental results better than Langevin theory. r

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Numerical calculations of the entropy and magnetization of magnetic fluids with chain aggregates

Cited by 5 publications

References 19 publications

The effect of the external magnetic field on the thermal relaxation of magnetization in systems of aligned nanoparticles

The effect of the external magnetic field on the thermal relaxation of magnetization in systems of aligned nanoparticles

Magnetic properties of colloidal suspensions of interacting magnetic particles

Effect of aggregates on the magnetization property of ferrofluids: A model of gaslike compression

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