Investigation of the complex susceptibility of magnetic beads containing maghemite nanoparticles (original) (raw)
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Nanoscale Research Letters
Method of determining of magnetic moment and size from measurements of dependence of the nonlinear magnetic susceptibility upon magnetic field is proposed, substantiated and tested for superparamagnetic nanoparticles (SPNP) of the "magnetic core-polymer shell" type which are widely used in biomedical technologies. The model of the induction response of the SPNP ensemble on the combined action of the magnetic harmonic excitation field and permanent bias field is built, and the analysis of possible ways to determine the magnetic moment and size of the nanoparticles as well as the parameters of the distribution of these variables is performed. Experimental verification of the proposed method was implemented on samples of SPNP with maghemite core in dry form as well as in colloidal systems. The results have been compared with the data obtained by other methods. Advantages of the proposed method are analyzed and discussed, particularly in terms of its suitability for routine express testing of SPNP for biomedical technology.
Magnetic Anisotropy of Maghemite Nanoparticles Probed by RF Transverse Susceptibility
Physics Procedia, 2015
We present radio frequency magnetic transverse susceptibility measurements on γ-Fe 2 O 3 nanoparticles, which yield an estimation of their effective anisotropy constant, K eff as a function of nanoparticle size. The resulting values range from 4 to 8 ×10 4 erg/cm 3 , being on the order of the magnetocrystalline anisotropy in bulk maghemite. K eff values increase as the particle diameter increases. Evidences of anisotropy field distribution given by the size distribution in the samples, and interparticle interactions that increase as the particle size increases, are also observed in the TS measurements. The effects of such interparticle interaction overcome those of thermal fluctuations, in contrast with the behavior of other iron oxide particles.
Static Magnetic Properties of Maghemite Nanoparticles
We report the static magnetic properties of Maghemite (γ-Fe2O3) nanoparticles with an average crystallite size of 14 ± 1.8 nm synthesized via a co-precipitation method. The zero-field-cooled (ZFC) and the field-cooled (FC) magnetization measurements were performed using a physical properties measurements system (PPMS) at temperatures from 5 K to 300 K. The ZFC/FC measurements showed a typical superparamagnetic behavior with a narrow size distribution.
RF Susceptibility Measurements of Magnetite Nanoparticles System
2010
In this study the design and set up of a very sensitive RF susceptometer based on a Robinson NMR oscillator is presented. This home-made susceptometer operates in a frequency range of 10-40 MHz and was successfully used to study thermal relaxation and particle interaction in magnetic nanoparticulated systems. Using this system we found the peak frequency associated to the energy absorption by the magnetite-based nanoparticulated material changing in the range of 17 to 28 MHz by applying a DC magnetic field up to 4 kOe.
Measurements are presented of the frequency-dependent (10 MHz–18 GHz) complex magnetic susceptibility of colloidal suspensions of different concentrations of nano-particles of magnetite in a hydrocarbon. Studies of three colloids, fluids, 1, 2 and 3, with packing fractions of magnetite particles of 0.22, 0.1 and 0.05, were made at different magnetic polarising fields in the range 0–100 kA m À1. It is shown that the fluid with the highest packing fraction exhibits the highest resonant frequency. Using a local field approximation it has been shown that this observation can be explained by simply considering magnetic interactions between individual particles in the fluid. It is not necessary to invoke the presence of clustering as a function of increased packing fraction.
The measurement of the frequency dependent susceptibility of magnetic colloids
Journal of Magnetism and Magnetic Materials, 1988
Since the 1960's technological interest in ferroflmds has grown rapidly, with a significant increase in experimental and theoretical research on their properties and applications. However, one aspect of this research, the measurement of the frequency-dependent, complex, relative susceptibility, x(o), has been almost overlooked Apart from one paper by Maiorov in 1979 and recent reports by Fannin et al. little research has been undertaken in this area. We report on a self-contained, computer controlled measurement system which makes possible the automatic measurement of this susceptibility over a very wide range of frequencies. Fifteen ferrofluids are examined and the experimental results are discussed. The magnetic analogue of the Cole-Cole plot is used in the presentation of complex susceptibility data. An important new fact is that in one of the magnetic colloids the Cole-Cole plot seems to be well described by the Cole-Davidson equation, which implies a definite upper limit to particle sire.
IEEE Transactions on Magnetics, 2000
Magnetic relaxation is exploited in innovative biomedical applications of magnetic particles such as magnetic particle imaging (MPI), magnetic fluid hyperthermia, and bio-sensing. Relaxation behavior should be optimized to achieve high performance imaging, efficient heating, and good SNR in bio-sensing. Using two AC susceptometers with overlapping frequency ranges, we have measured the relaxation behavior of a series of monodisperse magnetic particles and demonstrated that this approach is an effective way to probe particle relaxation characteristics from a few Hz to 10 MHz, the frequencies relevant for MPI, hyperthermia, and sensing.
Brownian rotational relaxation and power absorption in magnetite nanoparticles
Journal of Magnetism and Magnetic Materials, 2007
We present a study of the power absorption efficiency in several magnetite-based colloids, to asses their potential as magnetic inductive hyperthermia (MIH) agents. Relaxation times t were measured through the imaginary susceptibility component w 00 ðTÞ, and analyzed within Debye's theory of dipolar fluid. The results indicated Brownian rotational relaxation and allowed to calculate the hydrodynamic radius close to the values obtained from photon correlation. The study of the colloid performances as power absorbers showed no detectable increase of temperature for dextran-coated Fe 3 O 4 nanoparticles, whereas a second Fe 3 O 4 -based dispersion of similar concentration could be heated up to 12 K after 30 min under similar experimental conditions. The different power absorption efficiencies are discussed in terms of the magnetic structure of the nanoparticles. r