Switching skyrmions with VCMA/electric field for memory, computing and information processing
A fixed magnetic skyrmion in a memory or Boolean logic or non-Boolean computing element is reversibly switched or switchable (1) with only an electric field and without a magnetic field or spin current; and (2) using voltage control of magnetic anisotropy (VCMA) to reduce the spin current needed to switch the skyrmion. Some embodiments switch between four states: two skyrmion states and two ferromagnetic states. Other embodiments switch between two states which are both skyrmionic, in which case the switching process may use ferromagnetic intermediate states, or both ferromagnetic, in which case the switching process may use skyrmionic intermediate states, or between a Skyrmion and ferromagnetic state. Boolean and non-Boolean logic devices are also provided which are based on these switching methods.
1. A non-volatile magnetic element, comprising
a free layer having at least two stable states;
a fixed layer having a permanent magnetic state;
an oxide layer between the free layer and the fixed layer; and
a heavy metal layer configured to create Dzyaloshinskii-Moriya Interaction (DMI) at its interface with the free layer and thereby form a stable stationary skyrmion in the free layer.
2. The non-volatile magnetic element of claim 1 , wherein the at least two stable states of the free layer include a fixed core-up skyrmion and a fixed core-down skyrmion.
3. The non-volatile magnetic element of claim 1 , wherein the free layer has four stable states.
4. The non-volatile magnetic element of claim 3 , wherein the four stable states of the free layer are ferromagnetic up, ferromagnetic down, core-up skyrmion, and core-down skyrmion.
5. The non-volatile magnetic element of claim 4 , wherein all four stable states of the free layer are stable in an absence of an external magnetic bias.
6. The non-volatile magnetic element of claim 3 , wherein the stable states are one or more of thermally stable and stable in the presence of magnetic fields.
7. The non-volatile magnetic element of claim 1 , wherein the free layer is circular or elliptical or polygonal.
8. The non-volatile magnetic element of claim 1 , further comprising a top electrode arranged above the free layer, the fixed layer, the oxide layer, and heavy metal layer.
9. The non-volatile magnetic element of claim 8 , wherein the top electrode is annular or shaped as a circular or elliptical disk or polygonal shape.
10. The non-volatile magnetic element of claim 9 , wherein the top electrode is annular in shape and wherein the at least two states of the free layer include core-up skyrmion and core-down skyrmion, and the annular top electrode is configured for reading only a periphery of the core-up and core-down skyrmion states.
11. The non-volatile magnetic element of claim 1 , wherein the fixed layer is a ferromagnetic layer.
12. The non-volatile magnetic element of claim 1 , wherein the fixed layer is a stationary skyrmion layer.
13. The non-volatile magnetic element of claim 1 , further comprising a bottom electrode under the heavy metal layer.
14. The non-volatile magnetic element of claim 1 , wherein the heavy metal layer is configured to function as a bottom electrode for read/write operations.
15. The non-volatile magnetic element of claim 1 , further comprising a mechanism configured to apply a voltage waveform across the fixed layer, oxide layer, and free layer that causes a temporary increase or a temporary decrease in perpendicular magnetic anisotropy (PMA).
16. The non-volatile magnetic element of claim 15 , wherein the waveform applied by the mechanism is a bipolar waveform causing both the temporary increase in PMA and the temporary decrease in PMA.
17. The non-volatile magnetic element of claim 15 , wherein the non-volatile magnetic element is configured to pass a spin current across the fixed layer, oxide layer, and free layer concurrent with the application of the waveform.
18. The non-volatile magnetic element of claim 1 , wherein the element is configured to be or configured to be part of a memory element, a Boolean element, or a non-Boolean element.