Relative significance of particle anisotropy in systems of ultrafine ferromagnetic particles

Abstract

The relative weight of particle anisotropy in systems of dipolarly interacting single-domain ultrafine ferromagnetic particles is investigated based on the comparison between a simple model and a particular variant of it. The latter differs from the former by the absence of particle anisotropy, and both are investigated in parallel by Monte Carlo simulations of zero field cooling and field cooling experiments. By comparing systems characterized by different particle concentrations as well as by various types of particle positions' disorder, it is shown that the relative importance of the particle anisotropy, besides the expected dependence on the particle concentration, crucially depends on the positional disorder. (C) 2002 American Institute of Physics

Analysis of magnetic aftereffect by using Monte Carlo methods

“…As shown in Fig. 6 the magnetization depends approximately linearly on log t, which is in good agreement with the published experimental data [10] on magnetic viscosity.…”

“…It is remarkable that our simulations predict a maximum for the magnetization, which is in agreement with the existing experimental data and the computer simulations for magnetic materials (see for instance [10,11]). …”

“…By using this assumption we have conducted simulations experiments in which we start from an initial magnetic state and increase the "temperature" from 0 to relatively high values. These experiments are analogue to the zero-field-cooling (ZFC) measurements [10] in magnetic systems. In these measurements the sample is cooled down to very low temperatures after which a constant magnetic field x 0 is applied and the temperature is increased Fig.…”

Magnetic Properties of Mechanically Milled Sm-Co Permanent Magnetic Materials with the TbCu<SUB>7</SUB> Structure

“…The dipolar interaction strength also depends on the positional disorder present in the system. 30) The change in the morphology of the particles due to agglomeration, defects and microstructural changes introduced by milling may also have resulted in the decrease in the remanence ratio and enhanced dipolar interaction overcoming exchange interaction. The exchange interaction is found to depend on the exchange length which is only a few nm and hence much smaller compared to the single domain size which is of the order of a few hundred nanometer in Sm-Co type of permanent magnets.…”

Estudo do comportamento magnético de nanopartículas de magnetita e nanofios de níquel diluídos em cristais líquidos liotrópicos

“…Em trabalhos que buscam estudar a influência da interação dipolar entre partículas na magnetização total desses sistemas, é mais conveniente repre-sentar uma partícula como um único momento magnético, valendo-se do fato delas serem monodomínios. Em dois trabalhos de 2002 [29] e [30], Porto estudou a influência da anisotropia uniaxial, da desordem na posição das partículas e da interação dipolar, na temperatura de bloqueio extraídas de curvas ZFC-FC geradas por meio de simulações de Monte Carlo. Foi observado que em sistemas de nanopartículas com concentrações moderadas, a desordem posicional de partículas tem importância crucial no comportamento do sistema, aumentando T B quando tal desordem aumente [29].…”