Acquisition of vector hysteresis loops from micro-arrays of nano-magnets

A modified scanning Kerr microscope has been used as a static Kerr magnetometer to acquire in-plane vector hysteresis loops from square Si/Ta(50 Å)/Co₈₀Fe₂₀(40 Å)/Ni₈₈Fe₁₂(108 Å)/Ta(100 Å) elements with size ranging from 123 nm to 10 μm. The nanoscale elements were arranged in square arrays of 4 μm size. The laser beam was focused to a sub-micron spot, while polarization changes were recorded with an optical bridge detector containing a beam-splitting polarizer and two quadrant photodiodes. The coercive field exhibited a non-monotonic increase from 11 Oe in the 10 μm element to 170 Oe in the 123 nm elements. Loops acquired with the field applied parallel to the easy and hard in-plane uniaxial anisotropy axes were observed to become more similar in shape as the element size decreased.     

Macroscopic arrays of magnetic nanostructures from self-assembled nanosphere templates

We have extended the widely used technique of nanosphere lithography to produce nanosphere templates with significantly improved long-range order. Single, ordered domains stretching over areas greater than 1 cm2 have been achieved by assembling spheres with the correct surface chemistry on a water/air interface. Self-assembly over macroscopic areas is facilitated by a combination of electrostatic and capillary forces. The presented technique is easily implemented, and the assembled monolayers can be transferred onto almost any surface, thus making the procedure applicable to a broad range of nanoscale research. We demonstrate this through the fabrication of hexagonally ordered, macroscopic arrays of magnetic nanostructures with modified magnetic properties.