Determination of the effective anisotropy constant of magnetic nanoparticles – Comparison between two approaches

Kahmann, Tamara; Rösch, Enja Laureen; Enpuku, Keiji; Yonetani, Takashi; Ludwig, Frank

doi:10.1016/j.jmmm.2020.167402

Cited by 15 publications

(8 citation statements)

References 26 publications

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“…In this regard, the reason for the reducing the anisotropy constant in CGdFO and DGdFO MNPs is the weak interaction between Gd–Fe which decreased the ratio of orbital to spin moments of 4f electrons and further weakened the spin–orbit coupling . The decreasing trend of coercivity ( H c ) for the processed MNPs due to the lower value of the anisotropy constant ( k eff ), which can be explained via Stoner–Wohlfarth model …”

Section: Resultsmentioning

confidence: 99%

Influence of Controlled Dipolar Interaction for Polymer-Coated Gd-Doped Magnetite Nanoparticles toward Magnetic Hyperthermia Application

Hazarika,

Borgohain,

Borah

2024

ACS Omega

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To maximize heat release from immobilized nanoparticles (NPs), a detailed understanding of the controlled dipolar interaction is essential for challenging magnetic hyperthermia (MH) therapies. To design optimal MH experiments, it is necessary to precisely determine magnetic states impacted by the inevitable concurrence of magnetic interactions under a common experimental form. In this work, we describe how the presence of dipolar interaction significantly alters the heating mechanism of host materials when NPs are embedded in them for MH applications. The concentration of the NPs and the intensity of their interaction can profoundly impact the amplitude and shape of the heating curves of the host material. The heating capability of interacting NPs might be enhanced or diminished, depending on their concentration within the host material. We propose chitosan-and dextran-coated Gd-doped Fe 3 O 4 NPs directing dipole interactions effective for the linear regime to enlighten the pragmatic trends. The outcomes of our study may have substantial implications for cancer therapy and could inspire novel approaches for maximizing the effectiveness of MH.

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Section: Resultsmentioning

confidence: 99%

Influence of Controlled Dipolar Interaction for Polymer-Coated Gd-Doped Magnetite Nanoparticles toward Magnetic Hyperthermia Application

Hazarika,

Borgohain,

Borah

2024

ACS Omega

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“…Furthermore, in MNPs systems the magnetic anisotropy has contributions from crystal structure, surface [10,15], aspect ratio [16] and even from interparticle interactions [12,17]. There exist several experimental approaches from which the effective anisotropy constant (K eff ) value of a MNPs system could be obtained [8,13,18,19]. Most of these methods are temperature dependent d.c. magnetic field measurements.…”

Section: Introductionmentioning

confidence: 99%

Determination of the effective anisotropy of magnetite/maghemite nanoparticles from Mössbauer effect spectra

Henao¹,

Muraca²,

Sánchez³

et al. 2022

J. Phys. D: Appl. Phys.

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The stoichiometry and the effective anisotropy constant ($K_{eff}$) of several samples of iron-oxide nanoparticles (IONPs) with sizes between $12$ nm and $51$ nm, showing spheroidal and cubic shapes, were studied by means of Mössbauer spectroscopy at room temperature (RT). Mössbauer spectra were analyzed and fitted considering two magnetically split subspectra due to $Fe^{3+}$ and $Fe^{2.5+}$ ions in tetrahedral and octahedral sites of a non-stoichiometric magnetite, respectively. In order to take into account the collective fluctuations of the NPs magnetic moments, the measured Mössbauer spectra were fitted including a distribution of the hyperfine interactions associated with the NPs volume (V) distribution. To determine the $K_{eff}$ value, a direct comparison between the size distribution obtained from structural characterization techniques and the $K_{eff}V$ product obtained from Mössbauer spectra fitting was made. In this regard, the $K_{eff}$ value was determined as the one that maximizes the coincidence between the mean NPs sizes obtained by both methods. Finally, an overall surface anisotropy constant $K_s$ value was obtained by means of a linear relation between the mean NP size, the experimentally determined $K_{eff}$ and a weighted arithmetic mean magnetic anisotropy related with the bulk magnetite and maghemite anisotropy constants at RT. An evident relation between the $K_{eff}V$ values through the parameter $\lambda=K_{eff}V/k_BT$ and the magnetite/maghemite fraction in each sample was also observed.

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“…15 The use of different experimental conditions and SAR calculation methods, based on calorimetric data throughout the MFH literature, 15,42 further complicates the collection of representative data to determine the optimal system properties for heating. Limitations also apply to the characterization processes in which different methods are used to determine magnetic core size 43,44 and anisotropy, [45][46][47][48] potentially yielding different correlations of intrinsic properties to respective SAR values of experimental samples.…”

Section: Introductionmentioning

confidence: 99%

Using kinetic Monte Carlo simulations to design efficient magnetic nanoparticles for clinical hyperthermia

et al. 2021

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The purpose of this study was to identify the properties of magnetite nanoparticles that deliver optimal heating efficiency, predict the geometrical characteristics to get these target properties, and determine the concentrations of nanoparticles required to optimize thermotherapy. Methods: Kinetic Monte Carlo simulations were employed to identify the properties of magnetic nanoparticles that deliver high Specific Absorption Rate (SAR) values. Optimal volumes were determined for anisotropies ranging between 11 and 40 kJ/m 3 under clinically relevant magnetic field conditions. Atomistic spin simulations were employed to determine the aspect ratios of ellipsoidal magnetite nanoparticles that deliver the target properties. A numerical model was developed using the extended cardiac-torso (XCAT) phantom to simulate lowfield (4 kA/m) and high-field (18 kA/m) prostate cancer thermotherapy. A stationary optimization study exploiting the Method of Moving Asymptotes (MMA) was carried out to calculate the concentration fields that deliver homogenous temperature distributions within target thermotherapy range constrained by the optimization objective function. A time-dependent study was used to compute the thermal dose of a 30-min session. Results: Prolate ellipsoidal magnetite nanoparticles with a volume of 3922 ± 35 nm 3 and aspect ratio of 1.56, which yields an effective anisotropy of 20 kJ/m 3 , constituted the optimal design at current maximum clinical field properties (H 0 = 18 kA/m, f = 100 kHz), with SAR = 342.0 ± 2.7 W/g, while nanoparticles with a volume of 4147 ± 36 nm 3 , aspect ratio of 1.29, and effective anisotropy 11 kJ/m 3 were optimal for low-field applications (H 0 = 4 kA/m, f = 100 kHz), with SAR = 50.2 ± 0.5 W/g. The average concentration of 3.86 ± 0.10 and 0.57 ± 0.01 mg/cm 3 at 4 and 18 kA/m, respectively, were sufficient to reach therapeutic temperatures of 42-44 • C throughout the prostate volume. The thermal dose delivered during a 30-min session exceeded 5.8 Cumulative Equivalent Minutes at 43 • C within 90% of the prostate volume (CEM43T 90 ). Conclusion:The optimal properties and design specifications of magnetite nanoparticles vary with magnetic field properties. Application-specific magnetic nanoparticles or nanoparticles that are optimized at low fields are indicated for optimal thermal dose delivery at low concentrations.

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Determination of the effective anisotropy constant of magnetic nanoparticles – Comparison between two approaches

Cited by 15 publications

References 26 publications

Influence of Controlled Dipolar Interaction for Polymer-Coated Gd-Doped Magnetite Nanoparticles toward Magnetic Hyperthermia Application

Influence of Controlled Dipolar Interaction for Polymer-Coated Gd-Doped Magnetite Nanoparticles toward Magnetic Hyperthermia Application

Determination of the effective anisotropy of magnetite/maghemite nanoparticles from Mössbauer effect spectra

Using kinetic Monte Carlo simulations to design efficient magnetic nanoparticles for clinical hyperthermia

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