An XMCD-PEEM study on magnetized Dy-doped Nd-Fe-B permanent magnets

Abstract

We have succeeded in developing a method for photoemission electron microscopy (PEEM) on fully magnetized ferromagnetic bulk samples and have applied this technique to Dy-doped Nd-Fe-B permanent magnets. Remanence magnetization of the sample was approximately 1.2 T, and its dimension was 3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \times$</tex></formula> 3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\times$</tex></formula> 3 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{3}$</tex></formula> . By utilizing a yoke as an absorber of the stray magnetic field from the sample, we can obtain well-focused PEEM images of magnetized samples. We have observed not only chemical distributions to visualize Dy-rich and Dy-poor areas but also magnetic domains by x-ray magnetic circular dichroism. The formation of reversed magnetic domains is strongly suppressed at room temperature by Dy-doping. As the temperature of the Dy-doped sample is raised, starting from room temperature, the reversed magnetic domains first grow along the magnetization easy axis. Next, above approximately 80 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{ \circ}$</tex></formula> C, the shapes of reversed domains start to expand in the direction perpendicular to the easy axis. Above approximately 85 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> C, the reversed domains cover more than half of the field of view of 30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu$</tex></formula> m. More importantly, the reversed magnetic domains tend to nucleate or extend in Dy-poor regions. We discuss the relationship between the chemical distribution and the magnetic domain structure.