Permanent magnet comprising a stack of n patterns

A method of fabrication of a permanent magnet said method involving comprising:

• a) forming a stack comprising N patterns stacked one upon the other in a stack direction, where N is a whole number greater than or equal to two, each pattern comprising:
• a bottom antiferromagnetic layer,
• a top antiferromagnetic layer, and
• a ferromagnetic layer situated between the bottom and top antiferromagnetic layers,
• b) heating the stack so as to achieve a temperature greater than a temperature of ordering of the material of the magnetic layers of the stack,
• c) when the temperature is greater than the temperature of ordering, applying a first magnetic field to align the direction of magnetization of the ferromagnetic layers with a predetermined desired direction,
• d) cooling the stack in the presence of a second magnetic field less than the first magnetic field to cause an exchange coupling to appear between the ferromagnetic layer and the bottom or top antiferromagnetic layer of said pattern of the stack,
• wherein step a) comprises forming, at least once per group of ten consecutive ferromagnetic layers whose directions of magnetization are frozen by exchange coupling, a growth layer interposed between the top antiferromagnetic layer of the previous pattern and the bottom antiferromagnetic layer of the following pattern in the stack direction,
• said growth layer being directly in contact with said two top and bottom antiferromagnetic layers between which it is interposed,
• said growth layer being entirely realized in a nonmagnetic material chosen from the group made up of the following metals:
• Ta, Cu, Ru, V, Mo, Hf, Mg, NiCr and NiFeCr, or realized by a stack of several sublayers of nonmagnetic material disposed immediately on one another in the stack direction, at least one of said sublayers, known as the “metallic sublayer”, being entirely realized in a material chosen from said group, and
• the thickness of the growth layer being greater than 0.5 nm.