We describe the structure and method of formation of a STT MTJ or GMR MRAM
cell element that utilizes transfer of spin torque as a mechanism for changing the
magnetization direction of a free layer. The
critical current is reduced by constructing the free layer as a lamination comprising two ferromagnetic
layers sandwiching a
coupling valve layer. When the
Curie temperature of the
coupling valve layer is above the temperature of the
cell, the two ferromagnetic
layers are exchange coupled in parallel directions of their
magnetization. When the
coupling valve layer is above its
Curie temperature, it no longer exchange couples the
layers and they are magnetostatically coupled. In the exchange coupled configuration, the free layer serves to store data and the
cell can be read. In its magnetostatically coupled configuration, the cell can be more easily written upon because one of the layers can assist the spin torque transfer by its magnetostatic coupling. If the free layer is formed as a multi-layered lamination of N periodically repeating combinations of a ferromagnetic layer and a coupling valve layer, the
critical current can be reduced by a factor of N.