Mössbauer emission spectroscopy study of cobalt-surface-doped acicular magnetite particles

Abstract

Mössbauer emission spectroscopy was used to study cobalt deposited by alkaline precipitation on the surface of acicular magnetite particles. The samples closely resemble the cobalt-surface-doped particles currently used in magnetic recording tapes. A portion of the cobalt was found to be incorporated into a composition approximating that of cobalt ferrite (CoFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> ); this is the material responsible for increasing the coercivity of the particles. In samples having 0.33 and 3.3 percent (by weight) deposited cobalt, 85 percent and 34 percent, respectively, of the cobalt was found in CoFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> . The cobalt not incorporated into CoFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> was found in oxides and hydroxides, mainly in Co(OH) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and (probably) Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> . The amount of cobalt found in the form of CoFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> is correlated with the increase in coercivity that results from deposition. The possible origins of the uniaxial magnetic anisotropy of surface-doped oxide particles are discussed.