Morphological and magnetic characterization of electrodeposited magnetite

Chatman, Shawn Michael Edward (2005) Morphological and magnetic characterization of electrodeposited magnetite. Masters thesis, Memorial University of Newfoundland.

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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).

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