In the ferromagnetic phase, the atoms are magnetically aligned and their magnetic fields adds up. If you increase the temperature past a certain point though, the atoms are jiggled enough that they can no longer stay aligned and they 'point' in random directions, and their magnetic fields cancel out.
This is a big problem in hard drives: If you increase the temerature of a hard drive the magnetic regions no longer maintain their magnetization and your data gets erased. A lot of hard drive technology (eg 'perpedicular recording') has been developed to solve this problem.
From what I remember of my rusty high school chemistry magnetism requires a certain relatively stable configuration of the valence electrons. I'm guessing that as temperature increases it's impossible for the atoms (or even just the electrons) to maintain that configuration because of the increased energy. The electrons might even get excited enough to jump to entirely different orbitals, but I'm not sure if it works that way.
In the ferromagnetic phase, the atoms are magnetically aligned and their magnetic fields adds up. If you increase the temperature past a certain point though, the atoms are jiggled enough that they can no longer stay aligned and they 'point' in random directions, and their magnetic fields cancel out.
This is a big problem in hard drives: If you increase the temerature of a hard drive the magnetic regions no longer maintain their magnetization and your data gets erased. A lot of hard drive technology (eg 'perpedicular recording') has been developed to solve this problem.