Micron-size superparamagnetic iron-oxides watercress with unique MRI properties

In this work, 10-μm-sized superparamagnetic Fe3O4@(α, γ)−Fe2O3 watercress was synthesized by a one-step solvothermal method. Meanwhile, the other two kinds of micron-size hierarchical structures were also obtained by solely altering Fe2+/urea molar ratio in the same solvothermal procedure. It was found that the nuance of reaction parameters during synthesis can greatly alter the morphologies and structures of the obtained products, but it cannot alter their unique superparamagnetic properties at room temperature. Moreover, these large-size Fe3O4@(α, γ)−Fe2O3 products unexceptionally exhibit novel superparamagnetic-ferromagnetic transition around 30 K, indicating that the magnetic arrangement of Fe3O4 and (α, γ)−Fe2O3 components in these architectures are virtually the same. These micron-size iron oxides can beat the superparamagnetic size-limit (25-30 nm) of commonly-used Fe3O4 contrast agents in MRI application.