S-shaped Magnetic Configurational States in Individual Square Permalloy Particles

Zero-field magnetic configurations on the mesoscale depend significantly on particle size and shape as the exchange and magnetostatic energies become comparable. This results in systems that are neither single- nor multi-domain, but in a variety of possible configurational states, often with non-uniform magnetization but a net moment. As candidates for non-volatile memory and magnetic logic devices, understanding the allowed states and energies of these types of structures is paramount, while also providing a lens into the governing fundamental physics. Previous work has focused on arrays of particles, but this can obfuscate particular details of individuals.

We experimentally observe multiple stable configurational states in isolated ~200 nm square permalloy particles via the anisotropic magnetoresistance. Results are corroborated with micromagnetic simulations using mumax3. We observe a U-shaped configuration at zero field in larger particles with an applied field swept perpendicular to the square’s edge, and an S-shaped configuration at smaller sizes and for slightly off-axis field angles. This result indicates particles of this size cannot be described by a single collective coordinate as in larger particles, and instead the full configurational state must be considered.