R. Cherkaoui

Magnetic behaviour of γ-Fe2O3 nanoparticles by mössbauer spectroscopy and magnetic measurements

Abstractγ-Fe2O3 nanoparticles with varying state of dispersion in a polymer have been investigated by Mössbauer spectroscopy, static magnetic measurements at low applied field, and alternative susceptibility measurements over a large range of frequencies (2×10−2–104 Hz). The dynamical behaviour was characterized through the variation of the blocking temperature with the characteristic time of the measurement. The Mössbauer blocking temperature was determined according to a procedure described. For quasi-isolated particles an Arrhenius law is demonstrated. Effects of interparticle interactions in concentrated and aggregated systems are satisfactorily explained by the previous model. Dependence of the superparamagnetic susceptibility on the experimental conditions interpreted using the Lorentz or Onsager fields is mentioned.

Collective magnetic state in nanoparticles systems

Studies of static and dynamic properties of γ-Fe2O3 nanoparticles (4.7 nm) with interparticle interactions of increasing strength reveal a progressive change of regime from pure superparamagnetic, for very weak interactions, to collective for strong interactions. The collective regime presents a glass low-temperature state similar to the spin-glass state, but the glass transition shows distinct features.

Magnetic properties of isolated gamma -Fe/sub 2/O/sub 3/ particles

Noninteracting and interacting gamma -Fe/sub 2/O/sub 3/ particles are characterized by Mossbauer spectroscopy and magnetic measurements. The results raise various questions regarding the dynamics of the moments and the effects of the interactions. >

Mössbauer investigation of non-aggregated γ-Fe2O3 particles

Investigation by Mössbauer spectroscopy of non-aggregated nanometric γ-Fe2O3 particles dispersed in polymer is reported. Magnetic interactions between the particles were controlled by varying the particle concentration in the polymer. The results show that over the investigated range, the interactions make the relaxation time shorter. Infield experiments show spin canting which increases with decreasing particle size.

Magnetic dynamics of γ-Fe2O3 nanoparticles

Abstract The dynamical properties of γ-Fe2O3/polymer composites with particle size, aggregation state and concentration controlled independently have been studied by Mossbauer spectroscopy and various magnetic measurements. The main results are surveyed.

Collective glass state in a magnetic nanoparticle system

Studies of static and dynamic properties of γ-Fe2O3 particle (5 nm) assemblies reveal the existence of three magnetic regimes with increasing strength of the interparticle interactions: pure superparamagnetic for very weak interactions, modified superparamagnetic for weak-medium interactions, and collective for strong interactions. The last presents a low-temperature state similar to the spin-glass state, but the glass transition shows distinct features.

Static magnetic properties at low and medium field of gamma-Fe/sub 2/O/sub 3/ particles with controlled dispersion

/spl gamma/-Fe/sub 2/O/sub 3/ small particles (/spl les/10 nm) with various dispersion rates were studied by static magnetic measurements at low and medium applied fields. The results raise various questions concerning the determination of the non-relaxing magnetic moment and of the particle volume, the role of the particle surface and interactions. >

Thermoremanent magnetization of γ-Fe2O3 particles. Effect of interparticle interactions on the relaxation

Abstract The dynamical properties of a series of γ-Fe 2 O 3 nanoparticles (mean diameter: 7.1 nm) samples, with different aggregation states, have been studied by measuring the time decay of the thermoremanent magnetization at different temperatures. The effects of interparticle interactions on the temperature dependence of the relaxation rate are discussed. The results are in agreement with the proposed model.