Control of Double‐Vortex Domain Configurations in a Shape‐Engineered Trilayer Nanomagnet System

Abstract

Intense interest in nanomagnetic materials is stimulated by the continuing quest for smaller, faster, and more energy efficient magnetic devices. [1,2] Rapid miniaturization has pushed the physical dimensions of magnetic devices into the submicrometer region, where new and intriguing size-dependent phenomena take effect. [3][4][5] At this length scale, the exchange and magnetostatic energies are of comparable magnitude and small variations of size or shape in the nanomagnetic system dramatically alters the energy levels and ground-state spin configuration. Moreover, to achieve specific functionality, especially with multicomponent devices, the overall magnetization process must be precisely engineered to ensure reliable operation. [6,7] Accordingly, the ability to effectively probe and analyze complex multilayer spin configurations and magnetization processes plays a key role in the development of next-generation magnetic nanotechnologies.[8]Here, we focus on a novel nanometric trilayer structure consisting of two shape-engineered permalloy (Py, Ni 80 Fe 20 ) layers separated by a nonmagnetic aluminum (Al) spacer, as a model experimental system. Using electron holography techniques, as described in the Experimental section, we directly characterize the magnetization reversal behavior of individual trilayer stacks and show that separate chirality-controlled vortex nucleation and annihilation events in the two magnetic layers are responsible for the underlying reversal mechanism. Accordingly, we exploit this reversal behavior to systematically obtain four distinct configurations of flux-closure, double-vortex states at remanence that are controllably generated by applying defined magnetic-field sequences to individual nanomagnetic trilayer stacks.The flux-closure state is attractive in device application to minimize undesired interaction between neighboring nanomagnets.[9] Specifically, the magnetic vortex state is characterized by a planar curling of the magnetic spin configuration with a specific chirality (either clockwise (CW) or counter-clockwise (CCW)) around a nanometer-sized vortex region, wherein the magnetization achieves an out-of-plane spin polarity.[10] The magnetic vortex state is acquired (through nucleation) in the ground-state remanent configuration, for nanomagnets within a certain range of aspect ratios for the characteristic planar dimension and thickness.[11] Here, we combine a semi-square and semi-disk planar shape to control the vortex chirality upon nucleation as illustrated by micromagnetic simulations for a single-layer structure (Fig.

Simultaneous control of magnetic topologies for reconfigurable vortex arrays

“…Our result is unexpected and intriguing because only c has been considered controllable in asymmetric disks. [24][25][26][27][28] Simultaneous control of c and p is thought to be related to the asymmetric nature in the formation process of vortex states, as reported in our previous work. 7 It was found that two different vortex state groups with cp = +1 and Simultaneous control of magnetic topologies M-Y Im et al cp = − 1 are not energetically equivalent in a single circular disk due to both intrinsic and extrinsic factors.…”

“…Thus far, both static and dynamic studies on the control of vortex structures have been primarily dedicated to manipulation of either the c or p alone. 8,[21][22][23][24][25][26][27][28][29][30][31] A few attempts have been made to control both c and p, but these attempts have been conducted without repetition, meaning that only a single event of control has been investigated. 32,33 Therefore, reliability and repeatability for control of both topological features has not yet been addressed.…”

Chirality control via double vortices in asymmetric Co dots

“…Interestingly, asymmetric structures, e.g. nominally circular nanomagnets with a flattened edge 20,21 or triangularly shaped dots 22 , make chirality control possible. The broken symmetry leads to a preferred vortex nucleation site and subsequent chirality control.…”

Influence of the Distance between Nanoparticles in Clusters on the Magnetization Reversal Process

“…In this way, data storage density could be increased by increasing the number of bits per particle instead of increasing the particle density. This approach has also been followed by other groups, resulting in three, four, or up to eight magnetization states in diverse nanostructures [6][7][8][9][10].…”