Tunability and Ordering in 2D Arrays of Magnetic Nanoparticles Assembled via Extreme Field Gradients

• Published in: Advanced materials interfaces Vol. 9; no. 26
• Main Authors: Mohtasebzadeh, Abdul Rahman, Davidson, Jonathon C., Livesey, Karen L., Crawford, Thomas M.
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01-09-2022
• Subjects: 2D nanoparticle arrays; Assembly; Disk drives; hexatic phase; Magnetic moments; magnetic nanoparticles; Magnetic properties; magnetic recording; nanomanufacturing; Nanoparticles; perpendicular recording media; self‐assembly; Switches
• ISSN: 2196-7350; 2196-7350
• DOI: 10.1002/admi.202201056

Colloidal magnetite nanoparticles self‐assemble onto a disk drive medium as directed by magnetic field gradients created where the medium magnetic moment switches direction over single nanometer distances. Here, it is shown that for two such reversals or transitions that are closely spaced, the nanoparticles self‐assemble into a single feature centered between the transitions, rather than forming separate features at the transitions, and the resulting 2D assembly achieves hexatic ordering. Langevin dynamics simulations are used to explain these results, and it is found that the detailed magnetic properties of the medium play a critical role in determining assembly location. Slight changes to solvent polarity disrupt the hexatic ordering and push the nanoparticles toward the transitions, suggesting an alternate mechanism to precisely tune the self‐assembly process.
Magnetic nanoparticle self‐assembly is obtained by extreme field gradients at the surface of a hard disk drive medium. Experimental results, supported by simulations, show that small changes to colloidal properties of the particle solution and magnetic properties of the medium can dramatically transform the self‐assembly from 2D arrays with hexatic order to disordered features.