Investigations On Hydrothermally Synthesized Co3O4@MnxCo3-xO4 Core-Shell Nanoparticles

Ning Bian, Missouri State University

Abstract

Two different morphologies (pseudo-spherical shaped or PS type and hexagonal nanoplate shaped or NP type) and two different concentrations (0.07 M and 0.1 M) of manganese incorporated Co3O4@MnxCo3-xO4 core-shell nanoparticles (CSNs) were investigated, respectively. The motivation of this work is to investigate the magnetic properties of, and specifically the exchange bias, between different shaped CSNs and between different Mn-doped CSNs. A two-step synthesis method was utilized to obtain the CSNs: a soft chemical approach was used to obtain Co3O4 nanoparticles and a hydrothermal nano-phase epitaxy was used to obtain inverted bimagnetic core-shell nanoparticles. XRD results showed that F 3m crystal symmetry persists throughout the core region and the shell region for both of PS type and NP type CSNs. TEM-EDX results confirmed that manganese ions were successfully incorporated into the Co3O4 spinel structure of the CSNs. TEM and SEM result confirmed that there is no change in shape after the hydrothermal treatment. HRTEM results showed that the core and the shell can be easily distinguished by the interface between the two regions. Magnetic measurements showed that PS type CSNs have a higher coercivity and exchange bias than NP type CSNs at 5K. The XPS results confirmed that Mn ions were incorporated in the 2+ oxidation state in the CSNs.