We investigate the feasibility of the macrospin approximation to account for the actual shape of soft magnetic nanoparticles (MNPs) with realistic geometries. Specifically focusing on magnetite, we use the superellipsoidal parametrization to account for a variety of shapes, with a continuous interpolation from spherical to cubic morphologies, as well as different elongations. Our procedure consists of the direct comparison between angular-dependent hysteresis loops obtained by full micromagnetic simulations, with those produced by an extended Stoner–Wohlfarth (SW) model that incorporates both the intrinsic cubic magnetocrystalline anisotropy, and an effective uniaxial contribution arising from the particle elongation. Our results show that the extended SW framework provides quantitative agreement with micromagnetics over a broad range of particle volumes and aspect ratios, indicating that the effective uniaxial term captures the dominant shape-induced contributions. The limits of validity of the macrospin description are approximately 10–60 nm for axial ratios $r>1.5$, and 20–60 nm for $1.0<r<1.5$, with the upper limit associated with the onset of nonuniform magnetization states and the lower limit reflecting micromagnetic discretization limitations. These results establish a direct connection between nanoparticle morphology and effective macrospin parameters, demonstrating the suitability of the generalized SW model for describing the magnetic response of realistically shaped MNPs.

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• Ferromagnetism
• Magnetic order
• Magnetism
• Magnetization switching
• Micromagnetism