Thanks for sharing. I found this part interesting and could be...

Thanks for sharing. I found this part interesting and could be the reason why Hitachi have developed a higher revolution motor that uses a ferrite magnet

"Ferrite magnets have a higher Curie temperature than Neodymium magnets, so they maintain their magnetization better at higher temperatures. This gives designers greater operating margins at higher temperatures than Neodymium magnets offer.

Even though there are Neodymium magnets with high Coercivity for resistance to temperatures in excess of 200 degrees C, these temperature grades cost more than lower temperature grades. Ferrites can operate all the way up to 300 degrees C and their temperature coefficient actually increases by .27%/degree° C. This means that ferrites actually have stronger Coercivity as the temperature rises".