Systems and methods for implementing magnetoelectric junctions having improved read-write characteristics
View Patent ↗Embodiments of the invention implement MEJs having improved read-write characteristics. In one embodiment, an MEJ includes: ferromagnetic fixed and free layers, a dielectric layer interposed between the ferromagnetic layers, and an additional dielectric layer proximate the free layer, where the fixed layer is magnetically polarized in a first direction, where the free layer has a first easy axis that is aligned with the first direction, and where the MEJ is configured such that when subject to a potential difference, the magnetic anisotropy of the free layer is altered such that the relative strength of the magnetic anisotropy along a second easy axis that is orthogonal to the first easy axis, compared to the strength of the magnetic anisotropy along the first easy axis, is magnified during the application of the potential difference, where the extent of the magnification is enhanced by the presence of the additional layer.
1. A magnetoelectric junction comprising:
a ferromagnetic fixed layer;
a ferromagnetic free layer that is magnetically anisotropic;
a first dielectric layer interposed between the ferromagnetic fixed layer and the ferromagnetic free layer; and
a second dielectric layer disposed proximate the ferromagnetic free layer;
wherein the ferromagnetic fixed layer is magnetically polarized in a first direction;
wherein the ferromagnetic free layer has a first easy axis that is substantially aligned with the first direction, such that the ferromagnetic free layer can adopt a magnetic polarity that is either parallel with or antiparallel with the first direction; and
wherein the magnetoelectric junction is configured such that when a potential difference is applied across the magnetoelectric junction, the magnetic anisotropy of the ferromagnetic free layer is altered such that the relative strength of the magnetic anisotropy along a second easy axis that is orthogonal to the first easy axis, or the easy plane where there is no easy axis that is orthogonal to the first easy axis, as compared to the strength of the magnetic anisotropy along the first easy axis, is magnified or reduced for the duration of the application of the potential difference;
wherein the extent of the magnification or reduction of the relative strength is enhanced by the presence of the second dielectric layer.
2. The magnetoelectric junction of claim 1 , wherein the first direction coincides with an in-plane direction.
3. The magnetoelectric junction of claim 1 , wherein the first direction coincides with an out-of-plane direction.
4. The magnetoelectric junction of claim 1 , wherein the coercivity of the ferromagnetic free layer is reduced when a potential difference is applied across the magnetoelectric junction.
5. The magnetoelectric junction of claim 4 , wherein the application of a first threshold potential difference across the ferromagnetic fixed layer and the ferromagnetic free layer reduces the coercivity of the ferromagnetic free layer to an extent where the strength of the magnetic field imposed by the ferromagnetic fixed layer is sufficient to cause the ferromagnetic free layer to adopt a magnetic polarity that is determined by that of the ferromagnetic fixed layer.
6. The magnetoelectric junction of claim 5 , wherein the application of a second threshold potential difference that is greater in magnitude than the first threshold potential difference causes a spin-transfer torque current to flow through the magnetoelectric junction; wherein the spin-transfer torque current causes the ferromagnetic free layer to adopt a magnetic polarity that is in a direction antiparallel with the first direction.
7. The magnetoelectric junction of claim 1 , wherein the ferromagnetic fixed layer comprises one of: iron, nickel, manganese, cobalt, FeCoB, FeGaB, FePd, FePt, and mixtures thereof.
8. The magnetoelectric junction of claim 1 , wherein the ferromagnetic free layer comprises one of: iron, nickel, manganese, cobalt, FeCoB, FeGaB, FePd, FePt, and mixtures thereof.
9. The magnetoelectric junction of claim 1 , wherein the first dielectric layer comprises one of: MgO, Al 2 O 3 , and mixtures thereof.
10. The magnetoelectric junction of claim 1 , wherein the second dielectric layer comprises one of: MgO, Al 2 O 3 , HfO 2 , ZrO 2 , TiO 2 , TaO x , GdO x , and mixtures thereof.
11. The magnetoelectric junction of claim 1 , further comprising an externally applied magnetic field that is either parallel with or antiparallel with the magnetic polarization of the ferromagnetic fixed layer, wherein the externally applied magnetic field has a strength sufficient to cause the ferromagnetic free layer to adopt a magnetic polarity in a direction that is parallel with that of the externally applied magnetic field when the coercivity of the ferromagnetic free layer is reduced with the application of a potential difference across the ferromagnetic fixed layer and the ferromagnetic free layer.
12. The magnetoelectric junction of claim 1 , further comprising a second ferromagnetic fixed layer, wherein the second ferromagnetic fixed layer is disposed proximate the second dielectric layer.
13. The magnetoelectric junction of claim 1 , wherein the ferromagnetic free layer has a first side and an opposing second side, wherein voltage controlled magnetic anisotropy effects that are manifested at the first side and the opposing second side during the application of the potential difference, are cumulative.