Thermal spin torqure transfer magnetoresistive random access memory

1. A thermal spin torque transfer magnetoresistive random access memory (MRAM) apparatus, comprising:

a magnetic tunnel junction comprising a reference layer having a fixed magnetic polarity, a tunnel barrier layer, and a free layer on an opposite side of the tunnel barrier layer from the reference layer, the free layer comprising a first layer having a first Curie temperature and a second layer having a second Curie temperature different from the first Curie temperature; and

a tunnel junction programming circuit configured to apply a current through the magnetic tunnel junction to generate a write temperature in the magnetic tunnel junction and to write to the free layer of the magnetic tunnel junction.

2. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the first Curie temperature greater than the write temperature of the magnetic tunnel junction and the second Curie temperature is less than the write temperature of the magnetic tunnel junction.

3. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the first Curie temperature is greater than 150 degrees Celsius (° C.) and the second Curie temperature is less than 200° C.

4. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein both the first and second Curie temperatures are greater than a non-write operating temperature of the magnetic tunnel junction.

5. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the first and second layers have a combined thermal stability corresponding to a target magnetic polarization retention capability at a predetermined non-write operating temperature.

6. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the first layer has a magnetic energy between around 10 k B T and around 20 k B T, wherein k B is the Boltzmann constant and T is an ambient temperature.

7. The thermal spin torque transfer MRAM apparatus of claim 1 , further comprising:

a non-magnetic spacer between the first layer and the second layer.

8. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the free layer includes multiple first layers stacked in an alternating configuration with multiple second layers.

9. The thermal spin torque transfer MRAM apparatus of claim 1 , wherein the second layer has a higher thermal stability than the first layer at non-write operating temperature.

10. A magnetic tunnel junction of a thermal spin torque transfer magnetoresistive random access memory (MRAM) cell, comprising:

a reference layer having a fixed magnetic polarity;

a tunnel barrier layer; and

a free layer on an opposite side of the tunnel barrier layer from the reference layer, the free layer comprising a first layer having a first Curie temperature and a second layer having a second Curie temperature less than the first Curie temperature.

11. The magnetic tunnel junction of claim 10 , wherein the first layer has a Curie temperature greater than a write temperature of the magnetic tunnel junction and the second layer has a Curie temperature less than the write temperature of the magnetic tunnel junction.

12. The magnetic tunnel junction of claim 10 , wherein the first and second layers have a combined thermal stability corresponding to a target magnetic polarization retention capability at a predetermined non-write operating temperature.

13. The magnetic tunnel junction of claim 10 , wherein the first layer has a magnetic energy between around 10 k B T and around 20 k B T, wherein k B is the Boltzmann constant and T is an ambient temperature.

14. The magnetic tunnel junction of claim 10 , further comprising:

a non-magnetic spacer between the first layer and the second layer.