title: 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 2μm 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.
authors.affiliation: Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Vemulkar
authors.affiliation: Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Mansell
authors.affiliation: Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: D C M C
authors.initials: DC
authors.lastname: Petit
authors.affiliation: Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: R P
authors.initials: RP
authors.lastname: Cowburn
authors.affiliation: The Brain Tumor Center, The University of Chicago Pritzker School of Medicine , Chicago, Illinois 60637, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Lesniak