Depletion-Induced Chiral Chain Formation of Magnetic Spheres

Abstract

Experimental evidence is presented for the spontaneous formation of chiral configurations in bulk dispersions of magnetized colloids that interact by a combination of anisotropic dipolar interactions and isotropic depletion attractions. The colloids are superparamagnetic silica spheres, magnetized and aligned by a carefully tuned uniform external magnetic field; isotropic attractions are induced by using poly(ethylene oxide) polymers as depleting agents. At specific polymer concentrations, sphere chains wind around each other to form helical structures–of the type that previously have only been observed in simulations on small sets of unconfined dipolar spheres with additional isotropic interactions.

Sprayed Nanometer-Thick Hard-Magnetic Coatings with Strong Perpendicular Anisotropy for Data Storage Applications

“…Despite being the cheapest mass-market solution for years, the magnetic coating technology still requires further progress in optimizing the production pathways while retaining the high quality of the resulting medium. − To date, most of the efforts in technological improvement concern physical vapor deposition (PVD) of textured hexaferrite phases. ,, However, with PVD, crystal growth kinetics are limited by the deposition rate and post-treatment duration, slowing the tape spooling conveyor during processing. Sputter deposition provides in-plane texturing in the absence of any crystallographic relation of newly formed phases to the underlying substrates. , It diminishes an effective coercive force of the magnetic layer and results in spontaneous remagnetization of the adjacent grains …”