Magnetic memory devices and methods of writing data to the same
Magnetic memory devices include a magnetoresistive cell including a free layer having a variable magnetization direction and a pinned layer having a fixed magnetization direction, a bit line on the magnetoresistive cell and including a spin Hall effect material layer exhibiting a spin Hall effect and contacting the free layer; and a lower electrode under the magnetoresistive cell. A voltage is applied between the bit line and the lower electrode so that current passes through the magnetoresistive cell.
1. A magnetic memory device, comprising:
a magnetoresistive cell including a free layer having a variable magnetization direction and a pinned layer having a fixed magnetization direction;
a bit line on the magnetoresistive cell, the bit line including a spin Hall effect material layer exhibiting a spin Hall effect and an electrode material layer on the spin Hall effect material layer, the spin Hall effect material layer contacting the free layer, the bit line configured to allow a first current to flow therein;
a lower electrode below the magnetoresistive cell, the lower electrode is configured to allow a second current to pass through the magnetoresistive cell based on a voltage applied between the bit line and the lower electrode; and
a switching device configured to turn on and turn off a flow of the second current passing through the magnetoresistive cell such that a direction of the first current and a direction of the second current remain a same unipolar direction when changing the variable magnetization direction of the free layer.
2. The magnetic memory device of claim 1 , wherein, during writing of data,
the bit line is configured to allow the first current to flow along a first direction parallel to the free layer, and
the lower electrode is configured to allow the second current to pass through the magnetoresistive cell based on the applied voltage.
3. The magnetic memory device of claim 2 , wherein the free layer has in-plane magnetic anisotropy and has an easy axis tilted at 45 degrees relative to the first direction.
4. The magnetic memory device of claim 2 , wherein the first current and the second current are applied at different start times.
5. The magnetic memory device of claim 1 , wherein the spin Hall effect material layer includes at least one selected from platinum (Pt), tantalum (Ta), and tungsten (W).
6. The magnetic memory device of claim 5 , wherein the spin Hall effect material layer has a thickness greater than a spin diffusion length of a material of the spin Hall effect material layer.
7. The magnetic memory device of claim 1 , wherein the electrode material layer is made of a material having a resistivity less than a resistivity of the spin Hall effect material layer.
8. The magnetic memory device of claim 1 , wherein the free layer has perpendicular magnetic anisotropy.
9. The magnetic memory device of claim 1 , wherein the magnetoresistive cell is a magnetic tunneling junction (MTJ) cell.
10. The magnetic memory device of claim 1 , wherein the magnetoresistive cell includes:
a pinning layer made of an antiferromagnetic material;
the pinned layer on the pinning layer;
a non-magnetic layer on the pinned layer; and
the free layer on the non-magnetic layer.
11. The magnetic memory device of claim 10 , wherein
the pinned layer includes a first pinned layer, a second pinned layer, and a spacer layer between the first pinned layer and the second pinned layer,
the first pinned layer and the second pinned layer are made of a magnetic material and have the fixed magnetization direction, and
the first pinned layer, the spacer layer, and the second pinned layer collectively form a synthetic antiferromagnetic (SAF) structure.
12. The magnetic memory device of claim 10 , wherein
the free layer includes a first free layer, a second free layer, and a spacer layer between the first free layer and the second free layer,
the first free layer and the second free layer are made of a magnetic material and have the variable magnetization direction, and
the first free layer, the spacer layer, and the second free layer collectively form a free-SAF structure.
13. The magnetic memory device of claim 1 , wherein the switching device includes a transistor, a source electrode and a drain electrode, the source electrode or the drain electrode of the transistor is the lower electrode.
14. A method of writing data to a magnetic tunneling junction (MTJ) cell including a free layer having a variable magnetization direction and a pinned layer having a fixed magnetization direction, the method comprising:
applying a first current to a bit line contacting the free layer such that the first current flows along a direction parallel to the free layer and creates a spin current due to a spin Hall effect;
applying a second current to the free layer such that the second current creates a spin transfer torque which transfers the fixed magnetization direction of the pinned layer to the free layer, the second current configured to pass through the magnetic tunneling junction (MTJ) cell; and
turning on and turning off a flow of the second current passing through the magnetic tunneling junction (MTJ) cell such that the direction of the first current and a direction of the second current remain a same unipolar direction when changing the variable magnetization direction of the free layer, wherein,
the applying of the first current and the applying of the second current start with a time delay therebetween, proceed simultaneously during a set time interval, and end with the time delay therebetween.
15. The method of claim 14 , wherein the variable magnetization direction of the free layer has a first direction and a second direction rotated at 180 degrees from the first direction, the direction of the first current and the direction of the second current remain the same while reversing the variable magnetization direction from the first direction to the second direction and from the second direction to the first direction.
16. The method of claim 15 , wherein
the applying of the first current and the applying of the second current when the variable magnetization direction is reversed from the first direction to the second direction proceed with the time delay therebetween, and
the time delay has a reverse order when the variable magnetization direction is reversed from the second direction to the first direction.
17. The method of claim 14 , wherein the bit line includes a spin Hall effect material layer exhibiting the spin Hall effect and contacting the free layer.
18. The method of claim 17 , wherein
the bit line further includes an electrode material layer on the spin Hall effect material layer, and
the electrode material layer is made of a material having a resistivity less than a resistivity of the spin Hall effect material layer.
19. A method of writing data to a magnetic tunneling junction (MTJ) cell including a free layer and a pinned layer, comprising:
applying a first current to a conductive layer contacting the free layer such that a spin current is created in a direction substantially orthogonal to the first current based on a spin Hall effect induced by a spin Hall effect material in the conductive layer;
applying a second current that passes through the pinned layer to the free layer such that a spin transfer torque is created which transfers a fixed magnetic direction of the pinned layer to the free layer; and
turning on and turning off a flow of the second current passing through the magnetic tunneling junction (MTJ) cell such that a direction of the first current and a direction of the second current remain a same unipolar direction when changing a variable magnetization direction of the free layer.
20. The method of claim 19 , wherein the applying of the first current and the applying of the second current are started at different times.
21. The method of claim 19 , wherein the first current is applied in a direction substantially parallel to the free layer.
22. The method of claim 19 , wherein
the free layer and the pinned layer have in-plane magnetic anisotropy, and
the applying of the first current is performed such that an easy axis of the free layer tilts at an angle orthogonal to the direction in which the first current is applied.
23. The method of claim 22 , wherein the applying of the second current includes passing the second current through either a synthetic antiferromagnetic (SAF) structure in the pinned layer or a free-SAF structure in the free layer.
24. The method of claim 21 , wherein
the free layer and the pinned layer have perpendicular magnetic anisotropy, and
the applying of the first current is performed such that an easy axis of the free layer tilts at an angle orthogonal to the direction in which the first current is applied.