Experimental detection of multiple stable magnetic configurational states in isolated square permalloy particles of side length on the order of 200 nm is reported. The magnetic states are characterized using the anisotropic magnetoresistance via four-terminal resistance measurements of individual particles, and results are corroborated with micromagnetic simulations. The particles tend to relax into a ground state U-shaped “buckle” configuration at larger sizes and for an applied field swept parallel to the particle's edge, but assume an S-shaped configuration at smaller sizes and for slight variations in the applied field angle. The occurrence of this metastable state at room temperature indicates that typical models characterizing such particles in terms of energy landscapes or local effective fields may not be sufficient to accurately describe systems at this scale.
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We compute the resistance in arbitrary units here rather than using material parameters to calculate an exact resistance, as the overlap of the Au contacts with our particles means that the experimentally measured resistance is likely lower than would be calculated. Our primary concern is with how resistance varies with applied field, and, thus, computing simulated resistance in A.U. suffices here.
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).© 2022 Author(s). Published under an exclusive license by AIP Publishing.
2022
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