An investigation of magnetic oxides' defects and conflict of anisotropies for diluted powders

Abstract

Magnetostatic measurements and rotational hysteresis were carried out on extremely diluted samples of pure, surface modified, bulk doped iron oxides and CrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . It is found that in all these materials but pure γ-Fe <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">3</inf> a conflict of anisotropy is active. As a result, the values of remanence ratio j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> can be either lower or higher than the theoretical value of ½ for strictly uniaxial particles depending on the angle between the two anisotropy axis and the relative value of the anisotropy constants. It is therefore found that while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j_{r} &lt; 1/2</tex> for acicular magnetite and CrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , the introduction of cobalt always produces an increase of j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> : the extreme effect of such conflict can be found in high remanence isotropic particles. Such a conflict is minimized in Surface Modified Materials. From rotational hysteresis, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> vs. angle with applied field and, over all, from CF and IFF parameters, it is suggested that the postreatment of the iron oxides with the Co-containing solutions, beside the increase of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , has a beneficial effect on the morphology of the particles.