High coercivity Nd-Fe-B magnets with lower dysprosium content

Abstract

The elements Dy and Al play very important roles in the magnetic properties of Nd-Fe-B base compounds. The proper combination of Dy and Al may provide a significant improvement in the magnetic properties. With this in mind, close examinations have been made of the magnetic properties of several (Nd,Dy)-(Fe,Al)-B alloys. As a result, (Nd,Dy)-(Fe,Al)-B alloys containing equal atomic amounts of Dy and Al have been found to provide superior permanent magnetic properties. When compared to Nd-Dy-Fe-B or Nd-Fe-Al-B alloy of equivalent Dy or Al content, they have a much higher Hci . The reduction in Br associated with the addition is markedly less. The Hci of the alloys increases linearly with Dy content at a rate of about 7.5 kOe/at. % Dy, when the alloys contain equal atomic amounts of Dy and Al; or, approximately 1.4× the rate of (Nd,Dy)-Fe-B alloys. When Al is present, much less Dy is required to reach a given coercivity level. Thus, a magnet with high (BH)max and Hci can be more economically produced with Nd-Dy-Fe-Al-B alloys. The small Al additions, as described above, result in higher coercivities and lower irreversible losses at elevated temperatures without increasing temperature coefficients, and thus extend the application temperature range.