P. Mendoza Zélis

Determination of the blocking temperature of magnetic nanoparticles: The good, the bad, and the ugly

In a magnetization vs. temperature (M vs. T) experiment, the blocking region of a magnetic nanoparticle (MNP) assembly is the interval of T values were the system begins to respond to an applied magnetic field H when heating the sample from the lower reachable temperature. The location of this region is determined by the anisotropy energy barrier depending on the applied field H, the volume V, the magnetic anisotropy constant K of the MNPs and the observing time of the technique. In the general case of a polysized sample, a representative blocking temperature value

Structural and magnetic study of zinc-doped magnetite nanoparticles and ferrofluids for hyperthermia applications

T_B

Effects of the magnetoelastic anisotropy in Ni nanowire arrays

can be estimated from ZFC-FC experiments as a way to determine the effective anisotropy constant. In this work, a numerical solved Stoner-Wolfharth two level model with thermal agitation is used to simulate ZFC-FC curves of monosized and polysized samples and to determine the best method for obtaining a representative

Quasi-static magnetic measurements to predict specific absorption rates in magnetic fluid hyperthermia experiments

T_B

Magnetostrictive bimagnetic trilayer ribbons for temperature sensing

value of polysized samples. The results corroborate a technique based on the T derivative of the difference between ZFC and FC curves proposed by Micha et al(the good) and demonstrate its relation with two alternative methods: the ZFC maximum (the bad) and inflection point (the ugly). The derivative method is then applied to experimental data, obtaining the

A new application of Mössbauer effect thermal scans: determination of the magnetic hyperfine field temperature dependence

T_B

A constant-velocity Mössbauer spectrometer with controlled temperature sweep

distribution of a polysized

Surface and interface interplay on the oxidizing temperature of iron oxide and Au–iron oxide core–shell nanoparticles

Fe_3O_4

Dipolar interaction and demagnetizing effects in magnetic nanoparticle dispersions: Introducing the mean-field interacting superparamagnet model

MNP sample suspended in hexane with an excellent agreement with TEM characterization.

Study of Magnetic Materials by Mössbauer Thermal Scans. Application to Nanocrystalline Systems

Cubic-like shaped ZnxFe3−xO4 particles with crystallite mean sizes D between 15 and 117 nm were obtained by co-precipitation. Particle size effects and preferential occupation of spinel tetrahedral site by Zn2+ ions led to noticeable changes of physical properties. D ≥ 30 nm particles displayed nearly bulk properties, which were dominated by Zn concentration. For D ≤ 30 nm, dominant magnetic relaxation effects were observed by Mossbauer spectroscopy, with the mean blocking size DB ~ 13 to 15 nm. Saturation magnetization increased with x up to x ~ 0.1–0.3 and decreased for larger x. Power absorbed by water and chitosan-based ferrofluids from a 260 kHz radio frequency field was measured as a function of x, field amplitude H0 and ferrofluid concentration. For H0 = 41 kA m−1 the maximum specific absorption rate was 367 W g−1 for D = 16 nm and x = 0.1. Absorption results are interpreted within the framework of the linear response theory for H0 ≤ 41 kA m−1. A departure towards a saturation regime was observed for higher fields. Simulations based on a two-level description of nanoparticle magnetic moment relaxation qualitatively agree with these observations. The frequency factor of the susceptibility dissipative component, derived from experimental results, showed a sharp maximum at D ~ 16 nm. This behaviour was satisfactorily described by simulations based on moment relaxation processes, which furthermore indicated a crossover from Neel to Brown mechanisms at D ~ 18 nm. Hints for further improvement of magnetite particles as nanocalefactors for magnetic hyperthermia are discussed.