Magnetic tunnel junction (MTJ) memory device having a composite free magnetic layer
The various embodiments described herein include methods, devices, and systems for fabricating and performing operations on magnetic memory devices. In one aspect, a magnetic memory device includes: (1) a reference magnetic layer configured to have a first current threshold corresponding to a spin current level required to change a magnetic polarization of the reference magnetic layer; (2) a composite magnetic layer comprising a plurality of non-magnetic layers and a plurality of magnetic layers including a storage layer; and (3) a non-magnetic spacer layer between the reference magnetic layer and the composite magnetic layer; where the composite magnetic layer is configured such that the second current threshold is lowered, without decreasing thermal stability of the magnetic memory device, by spin current and/or coupling fields between adjacent magnetic layers of the plurality of magnetic layers.
1. A magnetic memory device, comprising:
a reference magnetic layer configured to have a first current threshold, the first current threshold corresponding to a spin current level required to change a magnetic polarization of the reference magnetic layer;
a composite magnetic layer comprising a plurality of non-magnetic layers and a plurality of magnetic layers including a storage layer having a first effective magnetization, wherein the plurality of magnetic layers is arranged in a stack such that: (a) the storage layer is closest to the reference magnetic layer, and (b) each successive layer from the storage layer in the plurality of magnetic layers has a more positive effective magnetization than the prior layer;
wherein the storage layer is configured to have a second current threshold, lower than the first current threshold, the second current threshold corresponding to a spin current level required to change a magnetic polarization of the storage layer;
wherein respective magnetic layers of the plurality of magnetic layers are separated by respective non-magnetic layers of the plurality of non-magnetic layers; and
wherein the composite magnetic layer is configured such that the second current threshold is lowered when transitioning the magnetic memory device between parallel and anti-parallel states, without decreasing thermal stability of the magnetic memory device, by at least one of spin current, and coupling fields between adjacent magnetic layers of the plurality of magnetic layers; and
a non-magnetic spacer layer between the reference magnetic layer and the composite magnetic layer.
2. The magnetic memory device of claim 1 , wherein the storage layer is connected to the reference magnetic layer via the non-magnetic spacer layer.
3. The magnetic memory device of claim 1 , further comprising a first terminal coupled to the reference layer and a second terminal coupled to the composite layer.
4. The magnetic memory device of claim 3 , further comprising a current source coupled to the first and second terminals, the current source configured to supply:
a first current adapted to facilitate determining the magnetic polarization of the storage layer;
a second current adapted to set the magnetic polarization of the storage layer to a first polarization; and
a third current adapted to set the magnetic polarization of the storage layer to a second polarization, distinct from the first polarization.
5. The magnetic memory device of claim 3 , further comprising a readout component coupled to at least one of the first terminal, and the second terminal, the readout component configured to determine whether a resistance between the first terminal and the second terminal exceeds a resistance threshold.
6. The magnetic memory device of claim 1 , wherein the non-magnetic spacer layer and each non-magnetic layer of the plurality of non-magnetic layers is composed of at least one of an insulator, and a non-ferromagnetic material.
7. The magnetic memory device of claim 1 , wherein the reference magnetic layer and each magnetic layer of the plurality of magnetic layers is composed of a ferromagnetic material.