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

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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.