اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدAC susceptibility as a tool to probe the dipolar interaction in magnetic nanoparticles
91
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The dipolar interaction is known to substantially affect the properties of magnetic nanoparticles. This is particularly important when the particles are kept in a fluid suspension or packed inside nano-carriers. In addition to its usual long-range nature, in these cases the dipolar interaction may also induce the formation of clusters of particles, thereby strongly modifying their magnetic anisotropies. In this paper we show how AC susceptibility may be used to obtain important information regarding the influence of the dipolar interaction in a sample. We develop a model which includes both aspects of the dipolar interaction and may be fitted directly to the susceptibility data. The usual long-range nature of the interaction is implemented using a mean-field solution, whereas the particle-particle aggregation is modeled using a distribution of anisotropy constants. The model is then applied to two samples studied at different concentrations. One consists of spherical magnetite nanoparticles dispersed in oil and the other of cubic magnetite nanoparticles embedded on PLGA nanospheres. We also introduce a simple technique to access the importance of the dipolar interaction in a given sample, based on the height of the AC susceptibility peaks for different driving frequencies. Our results help illustrate the important effect that the dipolar interaction has in most nanoparticle samples.
قيم البحث
اقرأ أيضاً
119Sn nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rate (1/T1) in SnO2 nanoparticles were measured as a function of temperature and compared with those of SnO2 bulk sample. A 15% loss of 119Sn NMR signal intensity for the nano
sample compared to the bulk sample was observed. This is indicative of ferromagnetism from a small fraction of the sample. Another major finding is that the recovery of the 119Sn longitudinal nuclear magnetization in the nano sample follows a stretched exponential behavior, as opposed to that in bulk which is exponential. Further, the 119Sn 1/T1 at room temperature is found to be much higher for the nano sample than for its bulk counterpart. These results indicate the presence of magnetic fluctuations in SnO2 nanoparticles in contrast to the bulk (non-nano) which is diamagnetic. These local moments could arise from surface defects in the nanoparticles.
In the context of magnetic hyperthermia, several physical parameters are used to optimize the heat generation and these include the nanoparticles concentration and the magnitude and frequency of the external AC magnetic field. Here we extend our prev
ious work by computing nonlinear contributions to the specific absorption rate, while taking into account (weak) inter-particle dipolar interactions and DC magnetic field. In the previous work, the latter were shown to enhance the SAR in some specific geometries and setup. We find that the cubic correction to the AC susceptibility does not modify the qualitative behavior observed earlier but does bring a non negligible quantitative change of specific absorption rate, especially at relatively high AC field intensities. Incidentally, within our approach based on the AC susceptibility, we revisit the physiological empirical criterion on the upper limit of the product of the AC magnetic field intensity $H_{0}$ and its frequency $f$, and provide a physicists rationale for it.
Using micron-sized Hall sensor arrays to obtain time-resolved measurements of the local magnetization, we report a systematic study in the molecular magnet Mn$_{12}$-acetate of magnetic avalanches controllably triggered in different fixed external ma
gnetic fields and for different values of the initial magnetization. The speeds of propagation of the spin-reversal fronts are in good overall agreement with the theory of magnetic deflagration of Garanin and Chudnovsky cite{Garanin}.
The role of dipolar interactions among Ni nanoparticles (NP) embedded in an amorphous SiO2/C matrix with different concentrations has been studied performing ac magnetic susceptibility Chi_ac measurements. For very diluted samples, with Ni concentrat
ions < 4 wt % Ni or very weak dipolar interactions, the data are well described by the Neel-Arrhenius law. Increasing Ni concentration to values up to 12.8 wt % Ni results in changes in the Neel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present.
The magnetic behavior of $Fe_{3-x}O_4$ nanoparticles synthesized either by high-temperature decomposition of an organic iron precursor or low-temperature co-precipitation in aqueous conditions, is compared. Transmission electron microscopy, X-ray abs
orption spectroscopy, X-ray magnetic circular dichroism and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulk-like magnetic and electronic properties, while nanoparticles synthesized by co-precipitation show much poorer crystallinity and particle-like phenomenology, including reduced magnetization, high closure fields and shifted hysteresis loops. The key role of the crystal quality is thus suggested since particle-like behavior for particles larger than about 5 nm is only observed when they are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or bio-distribution studies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
