A method for completely flipping magnetic domains in an artificial antiferromagnetic structure using electric current, a magnetic storage unit and a memory

Abstract

The present invention provides a method for completely flipping magnetic domains in an artificial antiferromagnetic structure by using electric current, wherein the antiferromagnetic structure comprises a first magnetic layer, a non-magnetic metal layer and a second magnetic layer stacked in sequence, and the method comprises the following steps: S1, connecting the antiferromagnetic structure to a circuit, applying a first direction current to the antiferromagnetic structure, and only partially flipping the magnetic domains in the first magnetic layer and the second magnetic layer; S2, applying a second direction current to the antiferromagnetic structure, and completely flipping the magnetic domains in the first magnetic layer and the second magnetic layer; wherein the first direction is opposite to the second direction. The method provided by the present invention can achieve complete flipping of magnetic domains by only using a combination of positive and negative currents without applying an external magnetic field, which reduces the device for applying a magnetic field compared to the prior art, greatly reduces the size of the device, and improves the integration of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic storage devices, and in particular to a method for completely flipping magnetic domains in an artificial antiferromagnetic structure by using electric current, a magnetic storage device and a storage unit thereof. Background Art

[0002] Both spin orbital torque MRAM (SOT-MRAM) and spin transfer torque MRAM (STT-MRAM) use current to flip the magnetic layer in the magnetic tunnel junction to achieve information writing. Compared with the two, spin orbital torque MRAM has more advantages. During the writing operation, the current does not flow through the tunneling layer, which significantly reduces the device breakdown caused by thermal effects. The spin orbit torque MRAM uses the spin-orbit coupling properties of heavy metals such as Pt or Ta to convert the current into spin current, and uses the spin current to flip the magnetic layer. However, to achieve the flipping of the magnetic layer, the symmetry of the magnetic moment in the plane must be broken, and an additional in-plane magnetic field is required, which makes it impossible for the device to achieve high integration. Later, researchers proposed a variety of ways to break the symmetry of the magnetic moment, such as using exchange bias or adding an in-plane magnetic layer, and the magnetic layer or heavy metal layer can also be grown into a wedge-shaped film to produce uneven spin currents to break the symmetry of the magnetic moment in the plane.

[0003] Several mechanisms proposed so far require additional effects to break the symmetry. These effects have been proven to be effective at the micrometer scale. However, to achieve high device integration, it is necessary to go to the nanometer scale. The device size is usually around 40nm. At this time, thermal disturbances will destroy additional effects such as exchange bias, and the wedge film process is no longer applicable at the nanometer scale. At present, SOT-MRAM still requires additional in-plane magnetic field sources, which seriously restricts the improvement of device integration and also makes it impossible to reduce energy consumption. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a method for achieving magnetic moment reversal without applying an external magnetic field and a magnetic device prepared thereby, so as to solve the problem that the prior art requires providing an additional in-plane magnetic field source.

[0005] According to a first aspect, an embodiment of the present invention provides a method for completely flipping magnetic domains in an artificial antiferromagnetic structure using an electric current, wherein the antiferromagnetic structure comprises a first magnetic layer, a non-magnetic metal layer, and a second magnetic layer stacked in sequence, wherein the non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer, and the first magnetic layer and the second magnetic layer are in an antiferromagnetic coupling state, and the method comprises the following steps:

[0006] S1, connecting the antiferromagnetic structure to a circuit, applying a current in a first direction to the antiferromagnetic structure, and only partially flipping the magnetic domains in the first magnetic layer and the second magnetic layer;

[0007] S2, applying a second direction current to the antiferromagnetic structure, so that the magnetic domains in the first magnetic layer and the second magnetic layer are completely reversed;

[0008] The first direction is opposite to the second direction.

[0009] Preferably, both the first magnetic layer and the second magnetic layer are perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the film surface.

[0010] Preferably, the non-magnetic metal layer comprises Ru;

[0011] Preferably, the non-magnetic metal layer has a thickness in the range of 1.25-1.75 nm.

[0012] Preferably, the first magnetic layer and the second magnetic layer include a Co / Pt artificial superlattice structure;

[0013] Preferably, the first magnetic layer comprises a [Pt / Co]n artificial superlattice structure, wherein n is a natural number greater than 1;

[0014] Preferably, the second magnetic layer comprises a [Co / Pt]m artificial superlattice structure, wherein m is a natural number greater than 1;

[0015] Preferably, m=n;

[0016] Preferably, the first magnetic layer comprises a [Pt(0.5nm) / Co(0.5nm)]n artificial superlattice structure;

[0017] Preferably, the second magnetic layer comprises a [Co(0.5nm) / Pt(0.5nm)]m artificial superlattice structure;

[0018] Preferably, in step S1 and step S2, the external magnetic field strength is -52 mT to 52 mT;

[0019] Preferably, in step S1 and step S2, the external magnetic field strength is zero.

[0020] Preferably, the magnitude of the current in the first direction is the same as the magnitude of the current in the second direction;

[0021] Preferably, the current in the first direction and the current in the second direction are in a range of greater than 30 mA;

[0022] Preferably, the first direction current and the second direction current are in the range of 30-50 mA.

[0023] Preferably, the partial reversal includes reversing 10%-90% of the magnetic domains in the first magnetic layer;

[0024] The flipping is flipping the magnetic moment direction of the magnetic domain in the first magnetic layer from the third direction to the fourth direction, and the fourth direction differs from the third direction by 180 degrees.

[0025] Preferably, the magnetic moment direction of the magnetic domain in the second magnetic layer remains unchanged;

[0026] The first-direction current and the second-direction current flow in a plane of the first magnetic layer.

[0027] The present invention also provides an artificial antiferromagnetic structure, the antiferromagnetic structure comprising a first magnetic layer, a non-magnetic metal layer and a second magnetic layer stacked in sequence, the non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer, the first magnetic layer and the second magnetic layer are in an antiferromagnetic coupling state,

[0028] Wherein, the thickness of the non-magnetic metal layer is in the range of 1.25-1.75 nm.

[0029] Preferably, the non-magnetic metal layer comprises Ru;

[0030] Preferably, the first magnetic layer and the second magnetic layer are both perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the first magnetic layer and the second magnetic layer;

[0031] Preferably, the first magnetic layer and the second magnetic layer include a Co / Pt artificial superlattice structure;

[0032] Preferably, the first magnetic layer comprises a [Pt / Co]n artificial superlattice structure, wherein n is a natural number greater than 1;

[0033] Preferably, the second magnetic layer comprises a [Co / Pt]m artificial superlattice structure, wherein m is a natural number greater than 1;

[0034] Preferably, m=n;

[0035] Preferably, the first magnetic layer comprises a [Pt(0.5nm) / Co(0.5nm)]n artificial superlattice structure;

[0036] Preferably, the second magnetic layer comprises a [Co(0.5nm) / Pt(0.5nm)]m artificial superlattice structure;

[0037] Preferably, a protective layer is provided on a side of the first magnetic layer away from the non-magnetic metal layer;

[0038] Preferably, a protective layer is provided on a side of the second magnetic layer away from the non-magnetic metal layer;

[0039] Preferably, the protective layer comprises Ta.

[0040] The present invention also provides a magnetic storage unit, which includes any one of the above antiferromagnetic structures.

[0041] The present invention also provides a magnetic memory, the magnetic memory comprising the above-mentioned magnetic storage unit;

[0042] Preferably, the magnetic memory includes a spin-orbit torque magnetic random access memory (SOT-MRAM).

[0043] The antiferromagnetic device provided by the present invention can first form an inclined magnetic domain wall under the action of a positive (or negative) current, and the device is in a state where two magnetic domains coexist, and then a negative (or positive) current is applied to make the inclined magnetic domain move in the opposite direction, thereby achieving a complete reversal of the magnetic domain. The method provided by the present invention can achieve magnetic domain reversal by only using positive and negative currents without applying an external magnetic field, greatly reducing power consumption; and because the setting of the magnetic layer for applying a magnetic field is reduced compared to the prior art, the size of the device is greatly reduced, and the integration of the device is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0045] Figure 1 Shown are the thin film structure diagram (side view) of the present invention (a), the hysteresis loop of the device (b), and a schematic diagram of the change of the device's magnetic domain with the external magnetic field (c).

[0046] Figure 2 The shape of the Hall Bar device of the present invention is shown (top view), the A and B electrodes are connected to a current source for providing current, and the C and D electrodes receive a voltmeter for detecting the Hall voltage.

[0047] Figure 3 The diagram shows how the device's magnetic domain changes with applied current when the device's external field drops from +200mT to -42mT (the external field points into the paper).

[0048] Figure 4 It shows a schematic diagram of the change of the device's magnetic domain with the applied current under an external field of -52mT (the external field points into the paper).

[0049] Figure 5 , Figure 6 It shows the effect of different current sizes on the domain wall shape under the same external field of -52mT.

[0050] Figure 7 Schematic diagram showing that light-colored and dark-colored magnetic domains can expand or contract only under the influence of an electric current.

[0051] Figure 8 Shown is a schematic diagram of the change in Hall signal of the Hall Bar in the state of all dark magnetic domains and all light magnetic domains generated by current pulses. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0053] The present invention proposes to use spin-orbit torque to flip the weakly coupled antiferromagnetic layer, and the complete flipping of the magnetic moment can be achieved by applying positive current and negative current alternately. Figure 1 (a) shows a thin film structure diagram (side view) of the present invention, as shown in FIG. Figure 1 As shown in (a), the specific structure of the film is Ta(5) / [Pt(0.5nm) / Co(0.5nm)]3 / Ru(1.3nm) / [Co(0.5nm) / Pt(0.5nm)]3 / Ta(5), wherein [Pt(0.5nm) / Co(0.5nm)]3 and [Co(0.5nm) / Pt(0.5nm)]3 are two perpendicular magnetization layers, i.e., the net magnetic moment directions of the magnetic domains of the two magnetic layers are perpendicular to the film surface; the thickness of Ru is 1.3nm, so that the two perpendicular magnetization layers (i.e., the first magnetic layer and the second magnetic layer) are in an antiferromagnetic coupling state, and after the device is prepared, the magnetic domains of the two magnetic layers will also present a single-domain antiferromagnetic coupling state. The magnetic domains mentioned below refer to these two states B1 (↑↓) and B2 (↓↑), which correspond to black and white in the figure respectively. The first arrow in the brackets of B1 (↑↓) and B2 (↓↑) indicates the net magnetic moment direction of a magnetic domain in the first magnetic layer, and the second arrow indicates the net magnetic moment direction of a magnetic domain in the second magnetic layer that overlaps with a magnetic domain in the first magnetic layer in the vertical direction. Although Figure 1The thickness of the Ru layer in (a) is shown as 1.3nm, but as long as its thickness is within the range of 1.25-1.75nm, the two magnetic layers can be in an antiferromagnetic coupling state. An artificial antiferromagnetic structure refers to a non-magnetic metal layer sandwiched between two ferromagnetic layers, so that the magnetic rectangles of the two ferromagnetic layers are antiparallel.

[0054] In a specific embodiment, the magnetic moments of two magnetic layers in antiferromagnetic coupling are not completely offset, that is, the net magnetic moment of the first magnetic layer is greater than the net magnetic moment of the second magnetic layer, so that the film presents a net magnetic moment in a first direction; after complete flipping, the first magnetic layer and the second magnetic layer are still in an antiferromagnetic coupling state, and the film presents a net magnetic moment opposite to the above-mentioned first direction.

[0055] Device preparation

[0056] The specific structure of the device is Ta(5) / [Pt(0.5) / Co(0.5)]3 / Ru(1.3) / [Co(0.5) / Pt(0.5)]3 / Ta(5), with the unit being nanometers. Ta is used as a base layer and a protective layer.

[0057] The device is grown on a lithographically prepared device ( Figure 2 On a silicon wafer (300nm thermal oxide layer) as shown in the figure, AJA's ultra-high vacuum magnetron sputtering device is used to first deposit 5 nanometers of Ta as a buffer layer, then a Pt / Co periodic structure, and finally a 5nm Ta as a protective layer.

[0058] After the growth is completed, the photoresist on the surface of the silicon wafer is cleaned with acetone ultrasonic wave, leaving only Figure 2 It should be emphasized here that the function of the device has very strict requirements on the thickness of Ru, and the thickness variation range must be controlled between 1.25-1.75nm.

[0059] Characterization of device characteristics

[0060] Magneto-optical Kerr microscopy is a technique that can be used to detect magnetic domains in magnetic films. It has the advantages of being accurate and real-time. This sample uses a magneto-optical Kerr microscope to characterize its magnetic domain distribution. Figure 1 (c) shows the change of the device magnetic domain with external magnetic field when no current is passed.

[0061] like Figure 2 As shown, the A and B electrodes of the device are connected to the positive and negative electrodes of the current source respectively, and the C and D electrodes are used to detect the Hall voltage by a voltmeter. The device is placed in the middle of a controllable uniform magnetic field of a magneto-optical Kerr microscope. The results of the hysteresis loop test show that the magnetic field magnitudes of the two reversals of the magnetic domain of this device are approximately ±126mT and ±138mT, as shown in Figure 1. Figure 1(b) As shown. Manually adjust the magnetic field, starting from the positive saturation 200mT, and gradually reduce the external magnetic field, as shown in Figure 1 As shown in (c), at 200mT, the sample is black (domain A). When the magnetic field is reduced to 126mT, a magnetic layer begins to flip, and a white domain B appears. As the magnetic field continues to decrease, the B domain occupies the entire device. It should be noted that there is a background processing during the test. Black and white are relative. For example, when the magnetic field drops to -135mT, the black and white at this time correspond to domains B and C respectively, and as the magnetic field drops to -138mT, the C domain basically occupies the entire device. The current flipping magnetic domain mentioned here is from domain B to domain C. The magnetic field is set to -42mT, and the current source connected to the sample passes 30mA current in the positive and negative directions to the electrodes on both sides of the sample. It is worth noting that the magnetic wall is non-volatile and does not require an external current to maintain this state. After the current becomes zero, the original shape of the oblique domain wall can still be maintained.

[0062] like Figure 3 As shown in the figure, the magnetic domain forms an oblique domain wall in the Hall bridge. The position and shape of the domain wall can be changed by changing the current and external magnetic field. Figure 3 As shown in (a), when no current is applied, the magnetic domain is the B1 domain. When a 30mA positive current is applied first, part of the B1 domain (accounting for about 60%-70% of the total domain) flips to the B2 domain. When a -30mA reverse current is applied further, all the B1 domain flips to the B2 domain, that is, the flip of all the domains is achieved by applying a positive current-reverse current. Similarly, the flip of all the B1 domains can also be achieved by first applying a reverse current and then a positive current, as shown in FIG. Figure 3 (b) In a specific embodiment, the current-passing time is in the order of seconds, and the time for passing the current in both the forward and reverse directions is roughly in the order of magnitude. In an optional embodiment, the time for passing the current in the forward direction is 1-10 seconds, and the time for passing the current in the reverse direction is 1-10 seconds.

[0063] The behavior of the device's magnetic domains is also related to the strength of the external magnetic field and the magnitude of the current. Figure 4 As shown in the figure, when the external magnetic field of the device drops from +200mT to -52mT and a 30mA current is passed, the shape of the domain wall changes, and it remains the same after the current is removed. Figure 4 As shown in the figure, under an external field of -52mT (External field is-52mT into the plane, -52mT external field points into the paper), when a 30mA positive current and then a -30mA reverse current are passed through the Hall bridge, when the 30mA positive current is passed, about 70%-80% of the B1 domains are flipped to B2 domains (as shown in the figure). Figure 4When a -30mA reverse current is first applied and then a 30mA forward current is applied, about 80%-90% of the B1 domains are flipped to B2 domains when a -30mA forward current is applied. Figure 4 (b)), and a reverse V-shape can be seen Figure 4 (b), but after passing 30mA positive current, the magnetic domain moment of the Hall bridge can be completely reversed.

[0064] Figure 5 , Figure 6 This shows the effect of different currents on the domain wall shape under the same -52mT field. Figure 5 , 6 As shown, when the forward current and reverse current are 31mA and 32mA respectively, the B1 magnetic domain can be completely flipped to the B2 magnetic domain.

[0065] like Figure 7 As shown in the figure, after the device reaches the negative saturation state with an external field of -200mT, the external field is adjusted to 60mT and a current of -30mA is passed, a similar Figure 4 The oblique magnetic wall. At this time, turn off the external field and use a reverse current of 30mA to expand the white magnetic domain and fill the entire Hall Bar. When a current of -30mA is passed again, the dark magnetic domain can expand. This process can occur in the absence of an external field, only under the action of current. The movement of the magnetic wall is also non-volatile. The Hall signals measured in these two states are recorded in Figure 8 When a -30 mA current is used to push out a full dark magnetic domain on the Hall Bar (the signal is about 0.448), the difference between the measured Hall signal and the Hall resistance in the full white magnetic domain state (the signal is about 0.256) is about 0.192.

[0066] This invention realizes the complete reversal of magnetic domains in the artificial antiferromagnetic structure of SOT without the need for an external in-plane magnetic field. The artificial antiferromagnetic structure is the pinning layer of the magnetic tunnel junction of the magnetic storage element, and is also the pinning layer in SOT-MRAM. Different from the method of using current to flip the free layer in SOT-MRAM, this invention proposes that current flipping of the artificial antiferromagnetic structure can also achieve full current writing and reading of high and low configurations. Compared with flipping the free layer, this invention does not require an additional in-plane magnetic field to break the symmetry, which is conducive to greatly improving the integration of the device and also helps to reduce energy consumption.

[0067] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations shall all fall within the scope defined by the appended claims.

Claims

1. A method for completely flipping the magnetic domains in an artificial antiferromagnetic structure using electric current, characterized in that: The antiferromagnetic structure comprises a first magnetic layer, a non-magnetic metal layer and a second magnetic layer which are stacked in sequence, the non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer, the first magnetic layer and the second magnetic layer are in an antiferromagnetic coupling state, and the method comprises the following steps: S1, connecting the antiferromagnetic structure to a circuit, applying a current in a first direction to the antiferromagnetic structure, and causing some magnetic domains in the first magnetic layer and the second magnetic layer to flip; S2, applying a second direction current to the antiferromagnetic structure, so that all magnetic domains in the first magnetic layer and the second magnetic layer are completely flipped; wherein the first direction is opposite to the second direction; In step S1 and step S2, the external magnetic field strength is zero.

2. The method according to claim 1, characterized in that: The first magnetic layer and the second magnetic layer are both perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the film surface.

3. The method according to claim 1 or 2, characterized in that: The nonmagnetic metal layer includes Ru.

4. The method according to claim 1 or 2, characterized in that: The first magnetic layer and the second magnetic layer include a Co / Pt multilayer film structure; The first magnetic layer comprises a [Pt / Co]n multilayer film structure, wherein n is a natural number greater than 1; The second magnetic layer comprises a [Co / Pt]m artificial superlattice structure, wherein m is a natural number greater than 1; The first magnetic layer comprises a [Pt(0.5nm) / Co(0.5nm)]n multilayer film structure; The second magnetic layer includes a [Co(0.5nm) / Pt(0.5nm)]m multilayer film structure.

5. The method according to claim 4, characterized in that m=n.

6. The method according to claim 1 or 2, characterized in that: The partial reversal includes reversing 10%-90% of the magnetic domains; The flipping is flipping the magnetic moment direction of the magnetic domain from the third direction to the fourth direction, and the fourth direction differs from the third direction by 180 degrees.

7. The method according to claim 3, characterized in that The thickness of the non-magnetic metal layer is in the range of 1.25-1.75 nm, so that the first magnetic layer and the second magnetic layer are in an antiferromagnetic coupling state.

8. An artificial antiferromagnetic structure, characterized in that: The antiferromagnetic structure comprises a first magnetic layer, a non-magnetic metal layer and a second magnetic layer which are stacked in sequence, the non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer, and the first magnetic layer and the second magnetic layer are in an antiferromagnetic coupling state. Wherein, the thickness of the non-magnetic metal layer ranges from 1.25 to 1.75 nm; When a current in a first direction is applied to the artificial antiferromagnetic structure and the external magnetic field intensity is zero, some magnetic domains in the first magnetic layer and the second magnetic layer can be flipped; When a current in a second direction is applied to the artificial antiferromagnetic structure and the external magnetic field intensity is zero, all magnetic domains in the first magnetic layer and the second magnetic layer can be completely flipped, and the first direction is opposite to the second direction.

9. The antiferromagnetic structure according to claim 8, characterized in that: The non-magnetic metal layer includes Ru; The first magnetic layer and the second magnetic layer are both perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the first magnetic layer and the second magnetic layer; The first magnetic layer and the second magnetic layer include a Co / Pt artificial superlattice structure; The first magnetic layer comprises a [Pt / Co]n artificial superlattice structure, wherein n is a natural number greater than 1; The second magnetic layer comprises a [Co / Pt]m artificial superlattice structure, wherein m is a natural number greater than 1; m=n; The first magnetic layer comprises a [Pt(0.5nm) / Co(0.5nm)]n artificial superlattice structure; The second magnetic layer comprises a [Co(0.5nm) / Pt(0.5nm)]m artificial superlattice structure; A first protective layer is disposed on a side of the first magnetic layer away from the non-magnetic metal layer; A second protective layer is disposed on a side of the second magnetic layer away from the non-magnetic metal layer; The first protective layer and the second protective layer include Ta.

10. A magnetic storage unit, characterized in that: The magnetic storage unit comprises the antiferromagnetic structure according to claim 8 or 9.

11. A magnetic memory, characterized in that: The magnetic memory comprises the magnetic storage unit according to claim 10; The magnetic memory includes a spin-orbit torque magnetic random access memory (SOT-MRAM).

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