Patent ID: 7345911

Claim:
A method to write and store information in a MRAM, comprising: providing a MTJ stack, including a first free layer, a first AFM layer, and a pinned layer that is magnetized in a fixed direction; providing a magnetic reference stack, including a second free layer that is exchange coupled to a second AFM layer having a blocking temperature; positioning said MTJ and magnetic reference stacks so that said first free layer is magnetostatically coupled to said second free layer; providing first and second bit lines that intersect and are orthogonal to one another; providing a word line that is not parallel to either bit line and that passes through said intersection; positioning said magnetic reference stack to be at said intersection; while heating said second AFM layer to a temperature above said blocking temperature, passing first and second electric currents, each current having a value that is one of a number of possible values, through said first and second bit lines respectively, thereby magnetizing said second free layer in a direction; through control of said current values, setting the direction of magnetization of the second free layer to be in one of said number of possible values; and then, while said bit and word line currents are still present, allowing said second AFM layer to cool to a temperature below said blocking temperature whereby said second free layer remains magnetized in said direction.