Micromagnetic Simulations of Exchange-Coupled Core–Shell Particulate Media

Abstract

Micromagnetic simulations are used to investigate the reversal of exchange-coupled magnetic core-shell particles and their application to particulate tape recording. With thin soft magnetic shells, the reversal of the core-shell particle remains of StonerWohlfarth type. We find that the thicker the shell or the higher its saturation magnetization, the larger the reduction of the particle switching field, in quantitative agreement with analytical predictions. Recording simulations are also performed for core/shell particulate media. This paper demonstrates that core-shell particles can provide broadband signal-to-noise ratio improvement over conventional single phase nanoparticles, while still satisfying thermal stability and writeability using conventional ring-type writers.

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…However, in spite of the potential strong role of the shape, there are only few theoretical studies devoted to hard-soft core/shell nanoparticles [105,107,226- 231]. Some simulations show that for hard/soft core/shell nanoparticles the evolution of H N on diverse parameters (e.g., shell thickness) follows quite closely the results expected from simple geometrical arguments (i.e., f hard /f soft ) [231].However, certain of these studies reveal, for example, large soft grains (in an inverse soft/hard structure) result in complex reversal or that the reduction of the interface coupling may enhance the spring-magnet type switching [228][229][230]. A recent systematic study of the effect of the hard/soft ratio for different nanoparticle sizes clearly evidences its important role on the magnetic properties (see Fig.…”

“…Patents on this type of structures can be found as late as the mid-1990s [76][77][78]. Interestingly, recent simulations on the use of core/shell nanoparticles for conventional recording have shown that this structure allows particle size reduction (which leads to improved SNR) without compromising thermal stability [231]. However, the current trend in hard-soft core/shell nanoparticles for recording is for single particle patterned media recording [64,[72][73][74][75][76][77]79].…”

Interplay between inter- and intraparticle interactions in bi-magnetic core/shell nanoparticles

“…In this context, the paper focuses on the interplay between inter-and intraparticle interactions in core/shell systems. We approach this issue by studying the magnetization reversal mechanisms in terms of the switching field distribution (SFD) [33], and the anisotropy energy barrier distribution [34][35][36]. Finally, Monte Carlo simulations were performed on interacting assemblies of these core/shell nanoparticles taking into account intraparticle (i.e.…”

Impact of core-shell dipolar interaction on magnetic phases of spherical core-shell nanoparticles

“…A recent micromagnetic study of hard/soft core-shell nanoparticles, with modest magnetization shells, with saturation magnetization Ms from 250 to 500 emu/cm 3 , revealed a Stoner-Wohlfarth behavior for the core-shell nanoparticle hysteresis loops [36]. In this case, due to the small value of the shell magnetization, dipolar effects are weak, and the angular dependence of the switching field follows the Stoner-Wohlfarth reversal mode [37].…”