Magnetic domain wall motion device based on modulation of spin-orbit torque

1. A magnetic domain wall (MDW) motion device, comprising:

a ferromagnetic layer with perpendicular magnetic anisotropy; and

a non-magnetic metal layer extending parallel to and in contact with the ferromagnetic layer,

wherein the ferromagnetic layer comprises first ferromagnetic regions, which are arranged in an extension direction of the ferromagnetic layer, and second ferromagnetic regions, which are provided between an adjacent pair of the first ferromagnetic regions,

wherein the first and second ferromagnetic regions have spin torque coefficients of opposite signs,

wherein an MDW positioned at an interface between the first and second ferromagnetic regions is moved by an in-plane current flowing through the non-magnetic metal layer,

wherein each of the first and second ferromagnetic regions comprises a notch that is provided at the interface between the first and second ferromagnetic regions in contact with each other and has a reduced width, and

wherein a narrowest portion of the notch is not aligned to the interface between the first and second ferromagnetic regions.

2. The MDW motion device of claim 1 , wherein the spin torque coefficients of the first and second ferromagnetic regions are determined by a structure or a constitution of the ferromagnetic layer.

3. The MDW motion device of claim 2 , wherein a sign of the spin torque coefficient of one of the first and second ferromagnetic regions is changed through doping of oxygen atoms.

4. The MDW motion device of claim 1 , wherein the non-magnetic metal layer comprises:

an upper non-magnetic metal layer provided to be adjacent to a top surface of the ferromagnetic layer; and

a lower non-magnetic metal layer provided to be adjacent to a bottom surface of the ferromagnetic layer.

5. The MDW motion device of claim 1 , wherein the notch comprises a first notch region with a rapidly decreasing width and a second notch region with a gently increasing width,

wherein the notch has a unit length corresponding to a length of the first or second ferromagnetic region,

wherein a start position of the first notch region is aligned to the interface between the first and second ferromagnetic regions, and

wherein an end position of the second notch region is aligned to another interface between the first and second ferromagnetic regions and is spaced apart from the start position of the first notch region by the unit length.

6. The MDW motion device of claim 1 , wherein the ferromagnetic layer further comprises an auxiliary pinning region provided near the interface between the first and second ferromagnetic regions, and

wherein the auxiliary pinning region is provided in such a way that its center is not aligned to the interface between the first and second ferromagnetic regions.

7. The MDW motion device of claim 6 , wherein the auxiliary pinning region comprises an impurity injected in the ferromagnetic layer, and

wherein the impurity comprises at least one of oxygen, fluorine, nitrogen, metal, transition metals, or gallium.

8. A magnetic domain wall (MDW) motion device, comprising:

a ferromagnetic layer with perpendicular magnetic anisotropy; and

a non-magnetic metal layer extending parallel to and in contact with the ferromagnetic layer, the non-magnetic metal layer comprising:

an upper non-magnetic metal layer provided to be adjacent to a top surface of the ferromagnetic layer; and

a lower non-magnetic metal layer provided to be adjacent to a bottom surface of the ferromagnetic layer,

wherein a thickness of the upper non-magnetic metal layer in the first non-magnetic region is different from that in the second non-magnetic region, and

wherein a thickness of the lower non-magnetic metal layer in the first non-magnetic region is different from that in the second non-magnetic region,

wherein the non-magnetic metal layer comprises first non-magnetic regions, which are arranged in an extension direction of the non-magnetic metal layer, and second non-magnetic regions, which are provided between an adjacent pair of the first non-magnetic regions,

wherein two portions of the ferromagnetic layer corresponding to the first and the second non-magnetic regions have spin torque coefficients of opposite signs, and

wherein an MDW positioned at an interface between the two portions of the ferromagnetic layer corresponding to the first and the second non-magnetic regions is moved by an in-plane current flowing through the non-magnetic metal layer.

9. The MDW motion device of claim 8 , wherein the ferromagnetic layer further comprises an auxiliary pinning region provided near the interface between the first and second non-magnetic regions, and

wherein the auxiliary pinning region is provided in such a way that its center is not aligned to the interface between the first and second non-magnetic regions.

10. The MDW motion device of claim 9 , wherein the auxiliary pinning region comprises an impurity injected in the ferromagnetic layer, and

wherein the impurity comprises at least one of oxygen, fluorine, nitrogen, metal, transition metals, or gallium.

11. A magnetic domain wall (MDW) motion device, comprising:

a ferromagnetic layer with perpendicular magnetic anisotropy; and

a non-magnetic metal layer extending parallel to and in contact with the ferromagnetic layer,

wherein the non-magnetic metal layer comprises first non-magnetic regions, which are arranged in an extension direction of the non-magnetic metal layer, and second non-magnetic regions, which are provided between an adjacent pair of the first non-magnetic regions,

wherein two portions of the ferromagnetic layer corresponding to the first and the second non-magnetic regions have spin torque coefficients of opposite signs,

wherein an MDW positioned at an interface between the two portions of the ferromagnetic layer corresponding to the first and the second non-magnetic regions is moved by an in-plane current flowing through the non-magnetic metal layer, and

wherein a thickness of the non-magnetic metal layer in the first non-magnetic region is different from that in the second non-magnetic region.

12. The MDW motion device of claim 11 , wherein the ferromagnetic layer comprises a notch whose width is locally reduced for each of the first and second non-magnetic regions, and

wherein a narrowest portion of the notch is not aligned to the interface between the first and second non-magnetic regions.

13. The MDW motion device of claim 12 , wherein the notch comprises a first notch region with a rapidly decreasing width and a second notch region with a gently increasing width,

wherein the notch has a unit length corresponding to a length of the first or second non-magnetic region,

wherein a start position of the first notch region is aligned to the interface between the first and second non-magnetic regions, and

wherein an end position of the second notch region is aligned to another interface between the first and second non-magnetic regions and is spaced apart from the start position of the first notch region by the unit length.

14. A nanowire, comprising:

a ferromagnetic layer with perpendicular magnetic anisotropy;

a non-magnetic metal layer extending parallel to and in contact with the ferromagnetic layer,

first and second regions which are alternately arranged in an extension direction of the nanowire,

wherein the first and second regions have spin torque coefficients of opposite signs, and

wherein an MDW of the ferromagnetic layer at an interface between the first and second regions is adapted to be moved by an in-plane current flowing through the non-magnetic metal layer; and

a motion direction selection unit configured to select a direction of motion of the MDW in a state in which the in-plane current is removed.

15. The nanowire of claim 14 , wherein the motion direction selection unit is a notch formed in the ferromagnetic layer, an impurity doped region formed in the ferromagnetic layer, or a magnetic field applying element additionally provided near the nanowire.

16. The nanowire of claim 14 , wherein the spin torque coefficient is spatially modulated by locally injecting oxygen impurities into the ferromagnetic layer or by locally modulating a thickness of the non-magnetic metal layer.

17. The nanowire of claim 14 , wherein the spin torque coefficient is spatially modulated by modulating an interface between the ferromagnetic layer and the non-magnetic layer.