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Domain structure of Nd-Fe-B magnet observed by PEEM

Magnetic domain structure and chemical distribution on the surface of Nd-Fe-B magnet have been observed by means of photoelectron emission microscope.  Nd-Fe-B magnet is known as the strongest permanent magnet composed mainly of Nd2Fe14B.  

(For more details, please see our paper, IBM J. Res. Dev. 55/4, 12/1-6 (2011).  [PDF])


Permanent magnet sample has been attached to a yoke made of pure iron as shown in (a).  This strongly suppressed the stray magnetic field from the sample and enabled PEEM measurement of a fully magnetized sample.  


Examples of the observed magetic domain structures are shown below.  (a) is for undoped Nd-Fe-B magnet whereas (b) is for Dy-doped Nd-Fe-B magnet, both taken at room temperature.  The light gray regions are magnetized in the direction of the yellow arrow labeled "Magnetized direction," which corresponds to the magnetization direction of the whole sample.  The dark gray regions are magnetized in the opposite direction and is called "reversed magnetic domains."


The magnetic domain structures observed along the heating process is shown below.  Up to 70 ºC (see (a)-(b)), the area of the reversed domains only gradually increases and the shape of the reversed domains tend to be longer in the direction of the easy magnetization axis, shown in red arrow in the figure above.   However, when temperature becomes higher than about 80 ºC, much wider reversed domains, as indicated by the yellow arrow, starts to be formed.  It is anticipated that this formation of wider reversed domains originates the rapid increase in the area of the reversed domains, shown in (j).  


Where does the wider reversed domains tend to nucleate?  Distribution of Fe and Dy has been measured as shown in (a) and (b) below.  Lighter color corresponds to larger concentration.  In (c), regions with smaller Fe are indicated in yellow and regions with smaller Dy is indicated in blue.  (c) is further overlaid on magnetic domain structures at 77-82 ºC in (d)-(f).  Wider reversed domains tend to be nucleated near the regions with smaller Dy concentration.  


Please see IBM J. Res. Dev. 55/4, 12/1-6 (2011/08) DOI:10.1147/JRD.2011.2159148.  [PDF] for more details.  


© Shin Imada 2014