Highly tunable perpendicularly magnetized synthetic antiferromagnets for biotechnology applications

Abstract

Magnetic micro and nanoparticles are increasingly used in biotechnological applications due to the ability to control their behavior through an externally applied field. We demonstrate the fabrication of particles made from ultrathin perpendicularly magnetized CoFeB/Pt layers with antiferromagnetic interlayer coupling. The particles are characterized by zero moment at remanence, low susceptibility at low fields, and a large saturated moment created by the stacking of the basic coupled bilayer motif. We demonstrate the transfer of magnetic properties from thin films to lithographically defined 2 m particles which have been lifted off into solution. We simulate the minimum energy state of a synthetic antiferromagnetic bilayer system that is free to rotate in an applied field and show that the low field susceptibility of the system is equal to the magnetic hard axis followed by a sharp switch to full magnetization as the field is increased. This agrees with the experimental results and explains the behaviour of the particles in solution.

The mechanical response in a fluid of synthetic antiferromagnetic and ferrimagnetic microdiscs with perpendicular magnetic anisotropy

“…The magnetic saturation process of the suspension is characterized by a linear magnetization response at low fields, followed by a distinct switch to saturation, 14 at…”

“…Perpendicularly magnetized materials have gained technological prominence because they offer large data retention times and fast domain wall speeds 6 for data storage devices, 7 high spin-orbit coupling effects for ultra low power logic and memory elements, [8][9][10] and the possibility of novel logic applications through interacting multilayers via antiferromagnetic (AF) interlayer exchange coupling. 11 While the behavior of magnetized permalloy vortex particles in a fluid has been investigated 12 because of interest in their potential as a novel cancer therapy, 13 the magnetic response of lithographically defined, perpendicularly magnetized particles 14 with antiferromagnetic interlayer coupling between magnetic layers, in a fluid and under an applied field has still not been fully characterized.…”

“…The magnetic microdiscs are fabricated by the patterning and lift off of magnetic thin films 14 formed by antiferromagnetically coupled interlayers of Co 60 Fe 20 B 20 and have a planar disc shape of 2 lm in diameter. The thin film system is modeled as two perpendicularly magnetized, AF coupled ferromagnetic (FM) layers, where the bilayer system is free to rotate in an applied magnetic field.…”

Magnetic particles with perpendicular anisotropy for mechanical cancer cell destruction

“…This basic structure is then repeated twelve times in order to increase the total moment 17 , giving a total magnetic thickness of 21.6 nm.…”

Versatile magnetic microdiscs for the radio enhancement and mechanical disruption of glioblastoma cancer cells

“…A new class of magnetic nanomaterials, in which manufacturing techniques usually used in microchip fabrication, have recently been investigated. 11,12 This new material class exhibits a high level of functionality without the need for complex external equipment. For example, the magnetic nanostructures can be manipulated, guided, concentrated, rotated, vibrated, assembled or disassembled with low magnetic elds.…”