Anisotropy and magnetization reversal with chains of submicron-sized Co hollow spheres

TL;DR

This study investigates the magnetic properties and anisotropy of chains of submicron Co hollow spheres, revealing significantly reduced anisotropy compared to bulk cobalt and elucidating the magnetization reversal mechanism.

Contribution

The paper provides new insights into the magnetic anisotropy and reversal processes in nanoscale hollow cobalt spheres, with detailed experimental analysis and comparison to bulk properties.

Findings

Effective anisotropy is an order of magnitude smaller than bulk cobalt.

Magnetization reversal follows a nucleation rotational mode.

Effective switching volume is approximately 2300 nm^3.

Abstract

Magnetic properties with chains of hcp Co hollow spheres have been studied. The diameter of the spheres ranges from 500 to 800 nm, with a typical shell thickness of about 60 nm. The shell is polycrystalline with an average crystallite size of 20 to 35 nm. The blocking temperature determined by the zero-field-cooling MZFC(T) measurement at H = 90 Oe is about 325 K. The corresponding effective anisotropy is determined as, Keff = 4.6*10^4 J/m^3. In addition, the blocking temperature and the effective anisotropy determined by the analysis on HC(T) are 395 K and 5.7*10^4 J/m^3, respectively. The experimentally determined anisotropy is smaller by one order of magnitude than the magnetocrystalline anisotropy of the bulk hcp Co, which is about 3 to 5*10^5 J/m^3. A further analysis on HC(T) shows that the magnetization reversal follows a nucleation rotational mode with an effective switching volume, V* = 2.3*10^3 nm^3. The corresponding effective diameter is calculated as 16.4 nm. It is slightly larger than the coherence length of Co, about 15 nm. The possible reason for the much reduced magnetic anisotropy is discussed briefly.