Does anybody have any idea about the type of magnet being used in BLDC motor?
There are a few main types of magnets used in motors, neodymium magnets and cheaper iron ceramic magnets(ferrite) and sometimes Alnico. Neos will be coated as the neo-iron-boron mixture oxidizes very rapidly, so dont scratch your magnet coating.
Usually high quality weight conscious motors use Neo magnets, and the 2213N 800Kv Brushless motor that i have seen looks to have nickel coated neodymium magnets in it. Im still waiting on my ROV kit to arrive. As per the particular grade of neodymium, i would bet that its probably NDFeB probabLy N42 grade, although running these underwater we could upgrade the to N52 to get more power and not have issues with the heat degradation.