Nd-Fe-B-Co-Al based permanent magnets with improved magnetic properties and temperature characteristics

Abstract

Magnetic properties of Nd-Fe-B-Co-Al alloy magnets have been studied with respect to both boron and aluminum concentration. Both cobalt and aluminum substitution for iron is remarkably effective for increasing magnetic hardness in the low boron concentration region. The following magnetic properties were attained for Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">62.5</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5.5</inf> Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> : Br=13.2KG, iHc=11.0kOe, (BH) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> =41.0MGOe and T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> =500°C. The reversible temperature coefficient of remanence in the above magnet was -0.071%/°., approximately one-half that for the Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">77</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf> magnet. It was observed that Laves phase Nd(Fe, Co) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> precipitates in cobalt containing magnets. The authors think that the addition of aluminum makes this Nd(Fe, Co) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> magnetic phase non-magnetic; which is considered to be the cause of coercivity increase.