English: Photomicrograph of NdFeB, the magnetic material used to make neodymium rare earth magnets, under a Kerr-microscope, showing the magnetic domain structure. The metal is composed of microscopic crystal grains. The domains are the light and dark stripes faintly visible within each grain. Due to magnetic anisotropy, the crystal lattice of each grain has an "easy" preferred direction of magnetization, and the domains form as stripes roughly parallel to this direction. The magnetization of light and dark domains is opposite, parallel to their long axis. In most of the grains the domains are parallel to the surface, but in the outlined grain the "easy" direction of magnetization is almost vertical, so only the ends of the domains are visible. ).