Relaxation in one-dimensional chains of interacting magnetic nanoparticles: Analytical formula and kinetic Monte Carlo simulations

Anand, Manish; Banerjee, Varsha; Carrey, Julian

doi:10.1103/physrevb.99.024402

Cited by 41 publications

(53 citation statements)

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“…They found the maximum heat dissipation in the case of aligned anisotropy axes. In a recent work, we have shown the relaxation time can be modulated by just varying the angle between the anisotropy axis and chain axis of MNPs [44]. In a another study, we have shown the Néel relaxation time can be enhanced or decreased by varying the anisotropy axes in the prefectly ordered system [45].…”

Section: Investigated the Anisotropy Axes Orientation Effect On The H...mentioning

confidence: 85%

“…In the presence of sufficient temperature T , each magnetic moment associated with a nanoparticle fluctuates between these two minima with oppositely directed magnetization by surmounting the energy barrier K eff V . Such magnetization fluctuation is characterized by a time scale known as the Néel relaxation time τ o N , which is given by the Arrhenius relation [44,53]…”

Section: Theoretical Frameworkmentioning

confidence: 99%

“…On the other hand, h d = 1.0 represents the strongest interacting system. The total energy of the system can be caculated using the following expression [44,56]…”

Section: Theoretical Frameworkmentioning

confidence: 99%

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Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Anand¹

2021

Preprint

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We study relaxation behaviour in the two-dimensional assembly of magnetic nanoparticles (MNPs) with aligned anisotropy axes and positional defects. The anisotropy axes orientation and disorder strength is changed by varying α and ∆, respectively. The magnetization decay does not depend on the aspect ratio A r of the system and ∆ for small dipolar interaction strength h d = 0.2. Remarkably, the magnetization decays rapidly for considerable h d with negligible ∆ and A r = 1.0. The dipolar interaction of enough strength promotes antiferromagnetic coupling in square ensembles of MNPs. There is a prolonged magnetization decay for large ∆ because of enhancement in ferromagnetic coupling. Notably, magnetization relaxes slowly for α < α even with moderate h d and a significant A r . Interestingly, the slowing down of the magnetic relaxation shifts to a lower α with h d = 1.0. The magnetization ceases to relax for α ≤ 60 • and h d ≤ 0.6 due to large shape anisotropy with A r = 400.0. Remarkably, a majority of the magnetic moment reverses its direction by 180 • for α > 60 • and large h d , resulting in the negative magnetization. The effective Néel relaxation time τ N also depends strongly on these parameters. τ N depends weakly on α and ∆ for h d ≤ 0.2, irrespective of A r . On the other hand, τ N decreases with α for significant h d provided α is greater than 45 • because of antiferromagnetic coupling dominance. In a highly anisotropic system, there is an enhancement in τ N with α (≤ 30 • ) even with moderate h d . While for α > 30 • , τ N decreases with α. These observations are useful in novel materials, spintronics based applications, etc.

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Section: Investigated the Anisotropy Axes Orientation Effect On The H...mentioning

confidence: 85%

Section: Theoretical Frameworkmentioning

confidence: 99%

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Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Anand¹

2021

Preprint

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“…This probability is the same used in Kinetic Monte Carlo calculations. [59][60][61] The second effect is the fluctuation of the magnetic moment within the same energy minimum, which results in the decrease of the effective magnetic moment, resulting in a statistical average of the magnetization vector projection in the direction of the applied field ( ). Taking these considerations in to account, the total average magnetization of the system as a function of time is given by: (8) where corresponds to the superparamagnetic contribution and 1 1 to the blocked one.…”

Section: Resultsmentioning

confidence: 99%

Adjusting the Néel relaxation time of Fe₃O₄/Zn _x Co_1−xFe₂O₄ core/shell nanoparticles for optimal heat generation in magnetic hyperthermia

et al. 2020

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In this work it is shown a precise way to optimize the heat generation in high viscosity magnetic colloids, by adjusting the Néel relaxation time in core/shell bimagnetic nanoparticles, for Magnetic Fluid Hyperthermia applications. To pursue this goal, Fe 3 O 4 /Zn x Co 1-x Fe 2 O 4 core/shell nanoparticles were synthesized with 8.5 nm mean core diameter, encapsulated in a shell of 1.1 nm of thickness, where the Zn atomic ratio (Zn/(Zn+Co) at%) changes from 33 at% to 68 at%. The magnetic measurements are consistent with a rigid interface coupling between the core and shell phases, where the effective magnetic anisotropy systematically decreases when the Zn concentration increases, without a significant change of the saturation magnetization. Experiments of magnetic fluid hyperthermia of 0.1 wt% of these particles dispersed in water, in Dulbecco modified Eagles minimal essential medium, and a high viscosity butter oil, result in a large specific loss power (SLP), up to 150 W/g, when the experiments are performed at 571 kHz and 200 Oe. The SLP was optimized adjusting the shell composition, showing a maximum for intermediate Zn concentration. This study shows a way to maximize the heat generation in viscous media like cytosol, for those biomedical applications that requiere smaller particle sizes .

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“…In the present study, we considered only the role of spin-dipolar interactions. Indeed, the importance of spin dipolar interactions was recognized earlier in molecular magnets [21,22]. Computing magnetization relaxation times from first principles is replete with problems such as computation of the matrix elements of the perturbation operator and computation of the phonon density of states.…”

Section: Introductionmentioning

confidence: 99%

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

Haldar

Ramasesha

2021

Phys. Rev. B

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Modeling blocking temperature in molecular magnets has been a long-standing problem in the field of molecular magnetism. We investigate this problem using a kinetic Monte Carlo (kMC) approach on an assembly of 100 000 short molecular magnetic chains (SMMCs), each of six identical spins with nearest-neighbor anisotropic ferromagnetic exchange interactions. Each spin is also anisotropic with an uniaxial anisotropy. The site spin on these SMMCs takes values 1, 3/2, or 2. Using the eigenstates of these SMMCs as the states of a Markov chain, we carry out a kMC simulation starting with an initial state in which all SMMCs are completely spin-polarized and assembled on a one-dimensional lattice so as to experience ferromagnetic spin-dipolar interaction with each other. From these simulations, we obtain the relaxation time τ r as a function of temperature and the associated blocking temperature. We study this for different exchange anisotropy, on-site anisotropy, and strength of dipolar interactions. The magnetization relaxation times show non-Arrhenius behavior for weak on-site interactions. The energy barrier to magnetization relaxation increases with an increase in on-site anisotropy, exchange anisotropy, and strength of spin dipolar interactions, more strongly on the last parameter. In all cases, the barrier saturates at large on-site anisotropy. The barrier also increases with site spin. The large barrier observed in rare-earth single ion magnets can be attributed to large dipolar interactions due to short intermolecular distances, due to their small size and large spin of the rare-earth ion in the molecule.

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Relaxation in one-dimensional chains of interacting magnetic nanoparticles: Analytical formula and kinetic Monte Carlo simulations

Cited by 41 publications

References 53 publications

Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Adjusting the Néel relaxation time of Fe₃O₄/Zn _x Co_1−xFe₂O₄ core/shell nanoparticles for optimal heat generation in magnetic hyperthermia

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

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Relaxation in one-dimensional chains of interacting magnetic nanoparticles: Analytical formula and kinetic Monte Carlo simulations

Cited by 41 publications

References 53 publications

Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects

Adjusting the Néel relaxation time of Fe3O4/Zn x Co1−x Fe2O4 core/shell nanoparticles for optimal heat generation in magnetic hyperthermia

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

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Adjusting the Néel relaxation time of Fe₃O₄/Zn _x Co_1−xFe₂O₄ core/shell nanoparticles for optimal heat generation in magnetic hyperthermia