Figure 4.

(a) Magnetic susceptibility (as the χT product) of “Fe₃OTFA” vs temperature. Solid line: best fit to the Hamiltonian (eq 1) with parameters g_i = 2.32, J₁₂ = J₁₃ = −28.7 cm^–1, J₂₃ = −43.2 cm^–1. Inset: ground state of an equilateral (frustrated) and an isosceles triangle. (b) Magnetization vs temperature of popcorn-shaped Fe_xO (x ≈ 0.94) NPs at 0.1 T, zero-field-cooled (ZFC, black squares) and field-cooled (FC, red circles). (c) Magnetization vs magnetic field of Fe_xO NPs at 2 K after zero-field cooling (ZFC, dotted black line) and after cooling in a field of 1 T (FC, solid blue line); magnetization at 300 K (red dashed line). Inset: expanded region around the origin.