Morphological and magnetic characterization of electrodeposited magnetite

Abstract

This thesis describes the synthesis, structure, morphology, and magnetic property relations of electrodeposited magnetite. Thin film magnetite was synthesized on polycrystalline brass or Au/Cr/glass substrates using an aqueous electrodeposition technique. Magnetite formation in electrolytes (containing KCH₃COO and Fe(SO₄)₂(NH₄)₂) required temperatures between 60°C and 85°C, and deposition potentials between -0.300 V and 0.575 V or galvanostatic current densities between 50 μA/cm² and 88 μA/cm². Magnetite crystallites had an octahedral habit when grown from electrolytes with low acetate concentrations, and a more rounded morphology when grown from acetate-enriched electrolytes. Magnetic hysteresis studies show that magnetite grown with lower acetate concentrations displays monotonically increasing coercivity (100-300 Oe), and monotonically decreasing squareness (80-35%), with increasing overpotential. In contrast, magnetite grown from acetate-enriched electrolytes had a much lower squareness (~ 25%) and coercivity (~ 50 Oe). This evidence suggests that potential and electrolyte composition can be adjusted to change domain behaviour from pseudo-single domain type (for low overpotentials and low acetate concentrations) to multi-domain type (for either high overpotentials or high acetate concentration). -- Magnetic hysteresis data also show that an exchange bias is present in samples containing both magnetite and iron oxide hydroxides. A preliminary study has shown that it is difficult to electrodeposit distinct bilayers of magnetite and the antiferromagnetic iron hydroxide goethite (α-FeOOH).