Magnetic random access memory and write method of the same

A magnetic random access memory comprising:

• a first magnetic layer comprising a magnetization fixed along one direction;
• a second magnetic layer on the first magnetic layer coupled with the first magnetic layer by exchange coupling;
• a nonmagnetic layer as a tunnel barrier on the second magnetic layer;
• a third magnetic layer on the nonmagnetic layer coupled with the second magnetic layer by exchange coupling, comprising a magnetization whose direction can be reversed by spin transfer through current injection;
• and
• a fourth magnetic layer on the third magnetic layer coupled with the third magnetic layer by exchange coupling, and comprising a magnetization whose direction can be reversed by spin transfer through current injection at a current density different from a current density for the third magnetic layer, wherein
• the memory comprises a magnetoresistive effect element in which the first magnetic layer, the second magnetic layer, the nonmagnetic layer, the third magnetic layer and the fourth magnetic layer form a magnetic tunnel junction exhibiting tunneling magnetoresistive effect, and configured to record and read out data of at least three levels.

A method for writing data to a magnetic random access memory which comprises a magnetoresistive effect element comprising at least one magnetic tunnel junction configured to indicate tunneling magnetoresistive effect, the method comprising:

• supplying current to the magnetoresistive element;
• and
• recording one of four levels which correspond to a first, a second, a third, and a fourth states which correspond to resistance of the magnetoresistive effect element in an ascending order, wherein
• the first state is set by supplying a writing current to the magnetoresistive effect element in a first direction;
• the fourth state is set by supplying the writing current to the magnetoresistive effect element in a second direction opposite to the first direction;
• the second state is set by supplying the writing current to the magnetoresistive effect element in the first direction in order to make the first state, and then supplying the writing current to the magnetoresistive effect element in the second direction;
• and
• the third state is set by supplying the writing current to the magnetoresistive effect element in the second direction in order to to make the fourth state, and then supplying the writing current to the magnetoresistive effect element in the first direction.