Dense chains of rounded-corners rectangular particles of lateral size 1025×450 nm2, with interparticle spacing variable in the range between 55 and 700 nm, have been patterned by deep UV lithography, followed by the lift-off of a permalloy film of thickness 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 configurations on the dipolar coupling. MFM measurements clearly show that closure states characterized by one, two or three vortices occur at remanence, together with the vortex/antivortex/vortex configuration (VAV, Fig. 1). The competition between intrinsic shape anisotropy and configurational anisotropy when particles are placed in chains head-to-tail has shown in previous studies that the formation of a regular sequence of single domain states is promoted by dipolar coupling and the vortex formation is inhibited or delayed during the reversal process. On the other hand, in the side-by-side configuration, dipolar interactions favour the nucleation of vortex states at remanence. In this work we concentrate on the nucleation and propagation processes of vortex states from one side of the particles to the other during the application of an external magnetic field. Fig. 2 displays changes in the MFM signal while a field applied along the hard direction is swept from positive to negative saturation, in the case of isolated particles. The detailed formation of single vortex and VAV states, taking place in a wide range of fields, can be followed. When the particles are put in chains head-to-tail the single domain state already shown to be present at remanence confirms its stability, but in a narrow range of fields most particles pass through the VAV configuration to attain magnetization reversal. This study can provide important information for the design of magneto-logic devices where interacting magnetic particles are considered to store and process information.
Nucleation and propagation of vortex states in dense chains of rectangular particles
BISERO, Diego;
2011
Abstract
Dense chains of rounded-corners rectangular particles of lateral size 1025×450 nm2, with interparticle spacing variable in the range between 55 and 700 nm, have been patterned by deep UV lithography, followed by the lift-off of a permalloy film of thickness 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 configurations on the dipolar coupling. MFM measurements clearly show that closure states characterized by one, two or three vortices occur at remanence, together with the vortex/antivortex/vortex configuration (VAV, Fig. 1). The competition between intrinsic shape anisotropy and configurational anisotropy when particles are placed in chains head-to-tail has shown in previous studies that the formation of a regular sequence of single domain states is promoted by dipolar coupling and the vortex formation is inhibited or delayed during the reversal process. On the other hand, in the side-by-side configuration, dipolar interactions favour the nucleation of vortex states at remanence. In this work we concentrate on the nucleation and propagation processes of vortex states from one side of the particles to the other during the application of an external magnetic field. Fig. 2 displays changes in the MFM signal while a field applied along the hard direction is swept from positive to negative saturation, in the case of isolated particles. The detailed formation of single vortex and VAV states, taking place in a wide range of fields, can be followed. When the particles are put in chains head-to-tail the single domain state already shown to be present at remanence confirms its stability, but in a narrow range of fields most particles pass through the VAV configuration to attain magnetization reversal. This study can provide important information for the design of magneto-logic devices where interacting magnetic particles are considered to store and process information.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
