Magnetization Reversal of Rectangular Particles: Closure States and Effect of Dipolar Coupling (original) (raw)
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Journal of Nanoparticle Research, 2011
Magnetostatic coupling in arrays of closely spaced magnetic elements is becoming an important issue in the path to the fabrication of spintronic devices. Dense chains of rounded-corners rectangular particles (dots) of lateral size 1025 9 450 nm 2 , with interdot spacing variable in the range between 55 and 700 nm, have been patterned by deep UV lithography, followed by the lift-off of two permalloy films of thickness 20 and 40 nm. Magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM) experiments, together with micromagnetic simulations, were performed to study the dependence of the magnetization configuration on the dipolar coupling. Both MOKE measurements and MFM images clearly show that, at remanence, the magnetic state of isolated particles of thickness 20 nm takes the form of a distorted single domain (C-state or S-State configurations). Instead, when the particle thickness is double (40 nm), closure states characterized by one, two or three vortices occur at remanence. However, when the 40 nm thick dots are placed in chains along the easy axis (head to tail), as the separation is progressively reduced, the single domain state is stabilized at remanence. On the other hand, when the 40 nm thick particles are placed side by side in chains the effect of dipolar interactions is to favour the nucleation of vortex states. For small inter-element separation, there is only one vortex per particle and it has the same chirality in adjacent particles, due to the dipolar interaction. Different from this, for the 20 nm thick samples and sub-100 nm separation, adjacent particles are single-domain but with antiparallel magnetization in neighbour elements, like in an artificial antiferromagnet.
Magnetostatic and exchange coupling in the magnetization reversal of trilayer nanodots
Journal of Physics D: Applied Physics, 2008
We present an experimental investigation of the magnetization reversal process in Ni 80 Fe 20 (10 nm)/Cu/Co(10 nm) sub-micrometric circular discs for two different thicknesses of the Cu spacer (1 and 10 nm). Magnetic hysteresis loops were measured by the longitudinal magneto-optical Kerr effect and by resonant scattering of polarized soft x-ray. The results for the 10 nm thick Cu interlayer show a complex magnetization reversal process determined by the interplay between the interlayer dipolar interaction and the different reversal nucleation fields in the two layers. It is worth noting that, during the reversal process, the magnetization of the two layers remains in a nearly single domain state due to the dipolar coupling. These findings are confirmed by three-dimensional micromagnetic simulations. In contrast, when the Cu spacer is 1 nm thick both measurements and simulations show that the reversal is accomplished via the formation of a vortex state in both discs due to the presence of a ferromagnetic exchange coupling that competes with the dipolar interaction.