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Core-shell nanostructures of Zinc and Cobalt ferrites synthesized by solution evaporation route are observed to perform novel magnetic response. The structural and morphological analyses of ZnFe 2 O 4− core / Fe 3 O 4− shell and CoFe 2 O 4− core / Fe 3 O 4− shell nanoparticles (NPs) are confirmed with X-ray diffractometer (XRD) and high resolution transmission electron microscopy (HRTEM). Physical properties measurement system (PPMS) investigations at room temperature reveal that the synthesized core-shell NPs (∼8 nm in diameter) are in super-paramagnetic state. The coercivity of ZnFe 2 O 4 / Fe 3 O 4 is much lower than that of CoFe 2 O 4 / Fe 3 O 4 NPs (e.g., at 5 K : H c = 0.6 kOe for ZnFe 2 O 4 / Fe 3 O 4 and H c = 18kOe for CoFe 2 O 4 / Fe 3 O 4 . Fe 3 O 4 is preferable to reduce magnetic hardness for Zinc ferrite and enhance for Cobalt Ferrite. [ABSTRACT FROM AUTHOR]

• Redox reaction between Co and CoO x. • Another voltage controlled magnetic storage scheme with data encoded in nanoparticle size. • Superparamagnetism can be used in magnetic storage. Electrochemical reaction induced by gate voltage between metallic cobalt and cobalt oxides was found to remarkably reshape average volume of superparamagnetic particles in Pt/Co/AlO x stacks at room temperature and thus modulate superparamagnetic properties, such as saturation fields and saturated magnetization, of the superparamagnetic films. The interfacial reaction was indicated in anomalous Hall transport measurement. This voltage-controllable superparamagnetism observed in Pt/Co/AlO x films could be utilized in a new architecture of nonvolatile and high density magnetic random access memories or neuromorphic computing. [ABSTRACT FROM AUTHOR]