Abstract
In this paper we present first-order reversal curve (FORC) diagrams of ensembles of three-dimensional Co3Fe nanostructures as 2 × 2 arrays of nano-cubes and nano-trees. The structures are fabricated and investigated by an advanced platform of focused electron beam induced deposition combined with high-resolution detection of magnetic stray fields using a home-built micro-Hall magnetometer based on an AlGaAs/GaAs heterostructure. The experimental FORC diagrams are compared to macrospin simulations for both geometries at different angles of the externally applied magnetic field. The measured FORC diagrams are in good agreement with the simulated ones and reflect non-uniform magnetization reversal dominated by multi-vortex states within, and strong magnetic coupling between, the building blocks of our nanostructures. Thus, a FORC analysis of small arrays of 3D magnetic nanostructures provides more detailed insights into the mechanisms of magnetization reversal beyond standard major hysteresis loop measurements.
Highlights
Magnetic nanostructures have become key building blocks in many areas of fundamental research in magnetism as well as in nano-technological fabrication of functional applications
We discuss first-order reversal curve (FORC) diagrams of our 3D CoFe nano-cubes and nano-trees, that have been investigated by global hysteresis loop measurements in Refs. 5 and 6
We present the first FORC diagrams for FEBIDfabricated 3D CoFe nanostructures grown as stem-mounted nanocubes and nano-trees directly on top of 5 × 5 μm2 Hall crosses of an ultra-sensitive micro-Hall sensor
Summary
Magnetic nanostructures have become key building blocks in many areas of fundamental research in magnetism as well as in nano-technological fabrication of functional applications. The attractiveness of the FORC method lies in its straightforward application to large ensembles of nanoscale magnets, such as arrays of interacting one- or two-dimensional magnetic nanostructures, see, e.g. Ref. 2–4. Accessing three-dimensional (3D) nanomagnetic structures with this method appears as a promising approach to probing the behaviour of the expected complex magnetization reversal processes. We have demonstrated the fabrication of building blocks for artificial magnetic lattices, aiming to advance beyond planar arrays toward the creation of 3D nanomagnetic networks, which were investigated experimentally by ultrasensitive micro-Hall magnetometers and simulated by macro- and micromagnetic approaches.. We discuss FORC diagram signatures of these ensembles of 3D Co3Fe (CoFe) structures as small (2 × 2) arrays of nano-cubes and nano-trees measured by micro-Hall magnetometry to gain further insights into the observed magnetic reversal processes. Experimental results are compared to simulations based on an idealized theoretical model using single-dipole macrospins (SDMS)
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