Magnetic properties of individual acicular particles

Abstract

A review is made of the work on the measurement and interpretation of the properties of individual particles, of the type incorporated into recording tape. It was shown that the remanent coercive force H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> (O) of particles of any of the materials measured covered a range of several hundred Oersted. A high proportion of the particies were multiple, that is they comprised several particles lying side by side: it is known that most of the particles in recording tape are of this type. An investigation was made of the nature of the reversal process, and of the origin of the range in H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> (O), for particles of 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> , CrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and metal powder (iron). The variation of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> (0) with angle between the field and particle axis was determined for 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> and CrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . The results of the above work were used in an attempt to synthesize the remanent loop of a tape from the knowledge of the properties of its constituent particles.