Heusler compounds with nonmagnetic spacer layers for forming synthetic antiferromagnets

Abstract

A device is described comprising a multilayer structure comprising three layers. The first layer is a magnetic Heusler compound, the second layer (serving as a spacer layer) is non-magnetic at room temperature and comprises alternating layers of Ru and at least one other element E (preferably: Al; or Ga or an alloy of Al with Ga, Ge, Sn or a combination thereof), and the third layer is also a magnetic Heusler compound. The composition of the second layer is expressed as Ru 1‑x E x , x is in the range of from 0.45 to 0.55. The MRAM element may be constructed by sequentially forming a substrate, the multilayer structure, a tunnel barrier, and an additional magnetic layer (whose magnetic moment is switchable).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 271,721, filed in the U.S. Patent and Trademark Office on February 8, 2019, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of magnetic random access memory (MRAM), and more particularly to MRAM devices relying on spin transfer torque, racetrack memory, and hard disk storage. Background Art

[0004] Heusler compounds are a class of materials with a representative formula X2YZ, where X and Y are transition metals or lanthanides, and Z is from a main group element. Due to the chemical distinction between X (or Y) and Z, they form a space group symmetry L21 (or D0) in which four face-centered cubic structures interpenetrate each other. 22 Heusler compounds have a unique structure defined by their tetragonal distortion. The properties of Heusler compounds strongly depend on the ordering of the elements that make up the compound. Therefore, the production of high-quality Heusler films typically requires high-temperature thermal processing, such as deposition at temperatures significantly above room temperature and / or thermal annealing at high temperatures (400°C or higher). Summary of the Invention

[0005] This paper discloses highly textured (epitaxial), very smooth, high-quality ultrathin bilayers of Heusler compounds separated by nonmagnetic template spacer layers that can be fabricated without thermal annealing processes. The template spacer layers are preferably formed from a Ru-Al binary alloy with a B2 structure (a cubic version of L10). The template layers can be deposited at room temperature and are well-ordered even at the deposited state (i.e., forming alternating atomic layers of Ru and Al).

[0006] Of particular interest are ultrathin bilayer films of Heusler compounds deposited with RuAl template spacer layers. These structures are highly epitaxial and ordered. The Heusler compounds disclosed herein form high-quality films with excellent magnetic properties, large perpendicular magnetic anisotropy, and square hysteresis loops (remanent magnetic moment in zero magnetic field approaches the saturation moment of each individual layer). These advantages are attributed to the B2 symmetry of the template layer and the L21 (or D0) of the Heusler layer. 22 An important property of structures made of ultrathin bilayers of Heusler compounds with a RuAl template spacer layer is that the relative orientation of the magnetic moments of the two Heusler layers depends on the thickness of the RuAl spacer layer. to and to Based on the previously observed periodicity of the basic oscillatory coupling between the Cr and Ru layers, the second thickness range of the antiparallel coupling of the magnetic moments is expected to be to This antiferromagnetic oscillatory coupling effect is not observed in the CoAl template spacer layer, where the magnetic moments of the two Heusler-containing layers are always parallel to each other, regardless of the spacer layer thickness, which is at least even above.

[0007] The most important characteristic of the template spacer layer is that it is composed of elements found in Heusler compounds. Thus, for example, any incorporation or diffusion of Al from a RuAl base layer into the Heusler-containing layer will not significantly alter the properties of the Heusler-containing layer because the Al comes from the class of "Z elements" that form Heusler compounds (see Background). Similarly, layers in which Al is partially replaced with other Z elements (e.g., Ga, Ge, and / or Sn) will be suitable for use as template spacer layers.

[0008] Another important property of the template spacer layer is that it can replicate the induced physical order of the first Heusler-containing layer, thereby promoting the ordering of the second Heusler-containing layer grown on top of the template spacer layer. The first Heusler-containing layer will inevitably have steps (see Figure 1 ), with atomic steps between adjacent terraces, which separate terraces with surfaces formed by X (or Y) from terraces formed by XZ (see Background for a discussion of X, Y, and Z). Due to the chemical affinity of X (or Y) for Al and Z for Ru, the first Heusler-containing layer will promote ordering of the template spacer layer, and for the same reasons mentioned above, will in turn promote ordering of the second Heusler-containing layer at moderate temperatures (even at room temperature), such as Figure 1 shown.

[0009] One embodiment of the present invention is a device comprising a multilayer structure. The structure comprises: a first layer comprising a first magnetic Heusler compound; a second layer which is non-magnetic at room temperature and which contacts and covers the first layer; and a third layer which contacts and covers the second layer. The third layer comprises a second magnetic Heusler compound. The second layer comprises Ru and at least one other element E, wherein the composition of the second layer is Ru 1-x E x, x is in the range of from 0.45 to 0.55. More preferably, x is in the range of from 0.47 to 0.53. In a preferred embodiment, E is aluminum, and the thickness of each of the first layer and the third layer is less than 5 nm or even less than 3 nm. The first Heusler compound and the second Heusler compound can advantageously be independently selected from Mn 3.1-x Ge、Mn 3.1-x Sn and Mn 3.1-x Sb group, for Mn 3.1-x For Sb, x is in the range of 0 to 1.1, and for Mn 3.1-x Ge and Mn 3.1-x For Sn, x is in the range of from 0 to 0.6. The first Heusler compound and / or the second Heusler compound may be a ternary alloy, for example, in the form of Mn 3.1-x Co 1.1-y Sn, where x≤1.2 and y≤1.0. In some embodiments, the magnetic moments of the first layer and the third layer are substantially parallel to (or perpendicular to) the interface between the second layer and the first layer and the interface between the second layer and the third layer, respectively. In addition, the magnetic moments of the first layer and the third layer may be substantially antiparallel to each other, wherein the thickness of the second layer is to Preferred embodiments of the device can be used as a memory element or as an element of a racetrack memory device.

[0010] Another embodiment of the present invention is a device comprising a substrate and a multilayer structure covering the substrate, wherein the structure comprises a first layer, a second layer, and a third layer. The first layer comprises a first magnetic Heusler compound, the second layer is non-magnetic at room temperature and comprises Ru and E (wherein E comprises at least one other element, wherein the at least one other element comprises Al, and the composition of the second layer is Ru 1-x E x , x is in the range of from 0.45 to 0.55), and the third layer comprises a second magnetic Heusler compound. The device also includes a tunnel barrier overlying the multilayer structure and an additional magnetic layer contacting the tunnel barrier, wherein the additional magnetic layer has a switchable magnetic moment. In a preferred embodiment, at least one of the first layer and the third layer comprises Co.

[0011] Yet another embodiment of the present invention is a device comprising a multilayer structure, the multilayer structure comprising a first layer, a second layer, and a third layer, wherein the first layer is magnetic and comprises a Heusler and / or L10 compound, the second layer is non-magnetic at room temperature and comprises Ru and E (E comprises at least one other element, the at least one other element comprising Al, and the composition of the second layer is Ru 1-x E x, x is in the range of 0.45 to 0.55), and the third layer is magnetic and comprises a Heusler and / or L10 compound. The L10 compound can advantageously be selected from the group consisting of MnGa, MnAl, FeAl, MnGe, MnSb, and MnSn alloys. Preferred embodiments of the device can be used as a memory element or a component of a racetrack memory device. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a conceptual diagram of a template using a double-layer Heusler compound separated by a RuAl spacer layer. X and X' represent transition metal elements, and Z and Z' represent main group elements.

[0013] Figure 2A Figure 2 is the XRD scan of three different stacks on MgO / MgO(001) substrate. The template layer was deposited at room temperature and annealed in situ at 400°C in vacuum.

[0014] Figure 2B yes Figure 2A P-MOKE hysteresis loop of the stack at room temperature.

[0015] Figure 3A Is with Thick Mn 2.3 Sb Heusler layer contact P-MOKE hysteresis loop of the sample with the template layer.

[0016] Figure 3B Is with Thick Mn3Ge Heusler layer contact P-MOKE hysteresis loop of the sample with the template layer.

[0017] Figure 4 The ones shown include Figure 2. P-MOKE hysteresis loop of a Heusler stack containing a RuAl spacer layer. The arrows indicate the magnetic moments of the two Heusler layers at different positions in the hysteresis loop.

[0018] Figure 5 are of thickness and Heusler stack of RuAl spacer layers (see Figure 5 P-MOKE hysteresis loop (left side of ).

[0019] Figure 6A is a Heusler stack with RuAl spacer layers inserted between them (see Figure 5P-MOKE hysteresis loop of the stacked structure shown).

[0020] Figure 6B is a Heusler stack with CoAl spacer layers inserted between them (see Figure 5 P-MOKE hysteresis loop of the stacked structure shown).

[0021] Figure 7A The thickness is and Heusler stack of RuAl spacer layers (see Figure 5 The P-MOKE hysteresis loop of the stacked structure shown in FIG. r 、V HighField and H SpinFlop .

[0022] Figure 7B is the H as a function of the thickness of the RuAl spacer layer SpinFlop changes.

[0023] Figure 7C is the remanent Kerr signal voltage divided by the Kerr signal voltage at saturation as a function of the thickness of the RuAl spacer layer.

[0024] Figure 8 is a Heusler stack with a RuAl spacer layer (see Figure 5 Anomalous Hall effect (AHE) measurements of a stacked structure).

[0025] Figure 9 is a Heusler stack with varying RuAl spacer layer thickness (see Figure 5 The remanence of the stack structure shown) State and saturation State-determined normalized anomalous Hall effect resistivity.

[0026] Figure 10A are from various Heusler stacks including CoAl spacer layers (see Figure 5 AHE signal of the stack structure shown, but with CoAl instead of RuAl as the spacer).

[0027] Figure 10B is the normalized AHE resistivity for a Heusler stack comprising a RuAl spacer layer and a CoAl spacer layer comparison.

[0028] Figure 10C is the normalized AHE resistivity from P-MOKE for a Heusler stack including RuAl and normalized V r / V sat comparison.

[0029] Figure 11 is a diagram of a magnetic tunnel junction device including a synthetic antiferromagnetic structure having a Heusler layer (and corresponding spacer layer) as described herein. DETAILED DESCRIPTION

[0030] New magnetic materials are needed to allow STT-MRAM (spin transfer torque - magnetic random access memory) to scale beyond the 20nm node. These materials must have a very large perpendicular magnetic anisotropy (PMA) and must be compatible with conventional CMOS technology for integration purposes. This magnetic material forms the electrode of a memory element based on a magnetic tunnel junction (MTJ). An important mechanism for switching the state of an MTJ element is to allow a spin-polarized tunneling current to pass through the MTJ. The size of this current is limited by the size of the transistor used to provide the write current. This means that the thickness of the electrode must be small enough to be switched by the available current. For ~1000emu / cm 3 To obtain a magnetization value of 1 nm, the electrodes must have a thickness of no more than about 1 nm.

[0031] Recently, it has been demonstrated that ultrathin Heusler layers (~1 nm thick) with bulk-like magnetic properties can be deposited using template layers such as CoAl, CoGa, CoSn, or CoGe (see U.S. patent application 15 / 660,681, filed on July 26, 2017, and U.S. Patent No. 10,177,305, issued on January 8, 2019). These ultrathin Heusler compound films, even down to a single unit cell thickness, exhibit perpendicular magnetic anisotropy and square hysteresis loops, making them promising candidates for use in STT-MRAM and racetrack memory applications. In both technologies, the use of synthetic antiferromagnets (SAFs) is advantageous. In STT-MRAM applications, the reference layer comprises an SAF structure because it exhibits very small fringe fields, which are the primary contributor to the offset fields observed in the measured hysteresis loops of the storage layer. In racetrack memory, the domain wall velocities in nanowires of SAF structures are significantly higher than those in nanowires of conventional ferromagnets. SAF structures derived from conventional ferromagnets use Ru as a nonmagnetic spacer layer. The family of tetragonal Heusler compounds, including Mn3Z (where Z = Ge, Sn, and Sb), has a layered structure of alternating layers of Mn-Mn and Mn-Z. The use of known elemental spacer layers (e.g., using only Ru) is not suitable for structures comprising two Heusler layers because elemental Ru cannot replicate the order of the Heusler layer below it; therefore, it cannot promote ordering of the second Heusler layer grown on top of the Ru spacer layer.

[0032] This paper discloses a spacer layer that promotes the formation of a SAF structure between Heusler compound layers. The results show that a RuAl alloy spacer layer with a CsCl structure induces antiferromagnetic coupling between two tetragonal Heusler compound layers separated by the spacer layer.

[0033] RuAl template layer

[0034] The DC magnetron sputtering method was used, and the base pressure was 2×10 -9 In Torr's ultra-high vacuum (UHV) chamber, Ru was grown 1-x Al x Single crystal epitaxial films of the alloy were prepared. Argon was used as the sputtering gas at a typical pressure of 3 mTorr. The films were deposited at room temperature using ion beam deposition (IBD) from a MgO target obtained from Kojundo Chemical Laboratories. The MgO buffer layer was prepared by depositing a thick layer of MgO. Alternatively, such a MgO buffer layer can be deposited by RF magnetron sputtering from a MgO target (Kojundo Chemical Laboratories) at room temperature. Then, a template layer (TL) of CoAl, CoAl / RuAl, or RuAl was deposited at room temperature. The TL was annealed at 400°C in ultrahigh vacuum for 30 minutes and then cooled to room temperature before depositing the subsequent layers, including the Heusler layer ( Mn3Sn) and MgO and The capping bilayer protects the layers below it when the entire stack is exposed to the environment. Figure 2A The compositions of the CoAl and RuAl layers are shown, which were determined to be Co, 51 Al 49 Ru 50 Al 50 Although a 1:1 RuAl layer composition is ideal in the present example, Ru with x in the range of 0.45 to 0.55 (more preferably, in the range of 0.47 to 0.53) 1-x Al x The layers will show a similar template effect (thus promoting the growth of alternating layers). Larger deviations are expected to make the growth of these alternating layer structures difficult or impossible.

[0035] X-ray diffraction (XRD) θ-2θ scans in out-of-plane geometry were performed on the films. Figure 2A Shown are a series of XRD scans for three films, namely: as well as The data show that the main CoAl(002) peak is at 2θ = ~65.5°, and the CoAl(001) peak is at 2θ = ~31.4°, the RuAl(002) peak is at 2θ = ~60.75°, and the RuAl(001) peak is at 2θ = ~29.3°. The presence of the CoAl(001) and RuAl(001) superlattice peaks clearly demonstrates that alternating stacking of Co and Al occurs; similarly, alternating layers of Ru and Al form. Although the template layer was annealed at 400°C for 30 minutes, it was found (not shown) that this annealing step was not required to promote the growth of alternating layers of Co / Al and Ru / Al. Substrate-associated x-ray diffraction peaks were observed for all samples and are labeled as MgO(002). The lattice parameters of the CoAl film are The lattice parameters of bulk CoAl are close to the B2 structure. The lattice parameters of RuAl film are The lattice parameters of bulk RuAl are close to those of the B2 structure.

[0036] Figure 2B The perpendicular magneto-optical Kerr effect (P-MOKE) signals obtained from these three films as a function of the applied magnetic field are shown. Square hysteresis loop of Mn3Sn. The RuAl layer shows an alternating layer structure (see XRD data above), while The Mn3Sn does not show any hysteresis loops. This is attributed to the large lattice mismatch (~7%) between RuAl and the Mn3Sn Heusler compound, which strains the Mn3Sn layer sufficiently that it no longer exhibits PMA. However, these data do indicate that the RuAl template layer is nonmagnetic. Depositing a RuAl layer on a CoAl layer strains the RuAl sufficiently to promote ordered, magnetic As measured by atomic force microscopy (AFM), these films are very smooth with a root mean square surface roughness (r rms ) is less than

[0037] Figure 3A shows the Mn grown on the RuAl template layer 2.3 P-MOKE hysteresis loop of Sb Heusler compound. The material stack of this sample is Similarly, Figure 3B The P-MOKE hysteresis loop of the Mn3Ge Heusler compound grown on a RuAl template layer is shown. The material stack of this sample is Mn 2.3 The spin polarizations of Sb and Mn3Ge are opposite to each other, like their Kerr constants, resulting in opposite signs of the P-MOKE signals of the two Heusler layers. This has an interesting consequence: when the two Heusler layers are independently aligned with the external field and then become parallel, the spin polarizations from Mn 2.3 The P-MOKE signal of the Sb and Mn3Ge bilayers decays when the field is swept. These results indicate that the RuAl template layer can promote the ordering of the Mn3Z Heusler compound (where Z = Ge, Sn, and Sb) to give it perpendicular magnetic anisotropy.

[0038] Figure 4 P-MOKE hysteresis loops obtained from a sample having two layers of different Heusler compounds separated by a nonmagnetic spacer layer of RuAl are shown. The stack of this sample is (where "t" represents thickness). Three distinct hysteresis loops are observed, and Figure 4 The arrows in the figure indicate the pairs of Mn3Ge and Mn 2.3 The magnetization orientation of the Sb layer. In a high-intensity field greater than 5kOe, the magnetizations of the two Heusler compounds are parallel to each other. In a zero-intensity field, in the remanent magnetization state, the magnetizations of the two Heusler compounds are antiparallel to each other. Therefore, the separation of the two Heusler compounds The presence of the RuAl spacer layer promotes the formation of a synthetic antiferromagnet (SAF). This is the first demonstration of a SAF structure based on Heusler compounds. Furthermore, the Heusler compounds and their corresponding spacer layers are deposited at room temperature and the resulting SAF structure does not require subsequent annealing. Furthermore, in the case of two layers of Heusler compounds with in-plane magnetic moments, the separation of the two Heusler layers is The presence of the RuAl spacer layer will also lead to the formation of a synthetic antiferromagnet (SAF). More specifically, the magnetic moment of the Heusler layer is substantially parallel to the interface between the Heusler layer and the RuAl spacer layer separating them. to , the magnetic moments of the two Heusler layers may be substantially antiparallel to each other.

[0039] Although the thickness of the Heusler layer in the SAF structure used herein is 1-2 nm, SAF structures with significantly thicker Heusler layers can be formed. For technically relevant SAF structures, it is desirable that the thickness of the Heusler layer be less than 5 nm, or even less than 3 nm.

[0040] Figure 5 The P-MOKE hysteresis loops measured from samples having two layers of different Heusler compounds separated by a nonmagnetic spacer layer of RuAl (with varying thickness t) are summarized. The stacks of these samples are of With t=0 and The RuAl sample shows a single square hysteresis loop, indicating ferromagnetic coupling between the Heusler layers. and In the RuAl sample, the coupling between the Heusler layers is antiferromagnetic.

[0041] Figure 6A and Figure 6B The P-MOKE hysteresis loops measured for samples with RuAl (see Figure 6A ) and CoAl (see Figure 6B ) of the two Heusler compounds separated by a non-magnetic spacer layer. The thickness of the spacer layer t is between 0 and The stacks of these samples are or The thickness of the RuAl spacer layer, t, is The increment range is from 0 to varies (only some data are shown) and the thickness of the CoAl spacer layer is and (Again, only some of the data are shown for clarity.) The hysteresis loops obtained for the sample with the CoAl spacer layer show a single square hysteresis loop for all CoAl thicknesses taken here, which is consistent with the hysteresis loops obtained for the sample with the RuAl spacer layer (see below). Figure 9 and Figure 10B The two Heusler layers separated by the CoAl spacer layer are ferromagnetically coupled for all thicknesses, and there is no evidence of the formation of a SAF structure.

[0042] exist Figure 7A 、 Figure 7B and Figure 7C The correlation of the hysteresis loops for samples with RuAl spacer layers is described in detail in . Figure 7A The hysteresis loops of the samples with RuAl spacer layers are shown. The thickness t of the RuAl spacer layer is 0. and The P-MOKE signal measured at H = 0 kOe is Vr (representing the remanent magnetization state), and the P-MOKE signal measured at a high field strength of ~1.4 T (not in the displayed region) is V HighField (indicates the saturation state), whose amplitude is shown by the black rectangle at much lower field strengths. When the field H is swept, the relative magnetization orientation of the two Heusler layers changes from parallel to antiparallel. H SF depends on the RuAl spacer layer thickness and is Figure 7A Indicated by solid black circles. Figure 7B Shows H SF With the change of RuAl spacer layer thickness. SF The sign of indicates the type of coupling between the two Heusler layers, which is negative for antiferromagnetic coupling and positive for ferromagnetic coupling. Therefore, based on the P-MOKE results, when t is about to Between and t at about to approximately Between (see also Figure 7C ), the coupling between the two Heusler layers is antiferromagnetic; for other thicknesses taken, the coupling is ferromagnetic. Figure 7C Shows V r With V sat The ratio of V sat =V HighField , and in the case of antiferromagnetic coupling V sat =V r +V HighField .

[0043] The Anomalous Hall Effect (AHE) signals of the above samples were measured in a Quantum Design DynaCool device at room temperature. Figure 8 These measurements are summarized in

[15] for Heusler layers separated by RuAl layers of varying thickness. The sample resistivity was measured using a standard Hall measurement geometry where wires were bonded to the four corners of a square sample (10 mm x 10 mm). The measured resistivity depends on the Lorentz force (which is linear with the applied field (H)) and the AHE. After subtracting the background from the resistivity data, the AHE was calculated at zero field. The AHE signal is determined at the maximum applied field (remanence, H = 0) and the AHE signal is determined at the maximum applied field. AH ) for the two Heusler compounds, in contrast, which is consistent with the P-MOKE measurements. The following three equations are used for the remanence State and saturation The AHE signal of the Heusler compound is determined in both states.

[0044]

[0045] Ferromagnetic (FM)

[0046] Antiferromagnetic (AFM)

[0047] Figure 9 Shows the ratio determined from AHE as a function of the RuAl spacer layer thickness. These results indicate that at small spacer layer thickness Under this condition, the coupling between the Heusler layers is ferromagnetic. to For spacer layer thicknesses in the range of to For a spacer layer thickness of 100 nm, the coupling becomes ferromagnetic again.

[0048] Figure 10A An AHE with a Heusler layer of CoAl as spacer layer is shown. Figure 10B The ratios are compared for the two spacer layers CoAl and RuAl like Figure 10B As shown, the ratio of these samples is ∼1 and is not affected by the thickness of the CoAl layer. When CoAl is used as the spacer layer, the coupling between the two Heusler compounds is ferromagnetic. Figure 10C Comparison of the ratios determined from AHE and P-MOKE or (V r / V sat ), and found that the ratio determined from AHE and P-MOKE or (V r / V sat ). Therefore, the RuAl spacer layer enables antiferromagnetic coupling between the two Heusler layers, leading to a synthetic antiferromagnet for a suitable RuAl thickness.

[0049] The structural order of the ultra-thin layer may be due to the different chemical properties of the Ru and Al elements in the template spacer layer. As an alternative to Al, Al alloys such as AlSn, AlGe, AlGa, AlGaGe, AlGaSn, AlGeSn and AlGaGeSn can be used. Binary (X=Y) and ternary Heusler alloys are composed of two / three different types of atoms, respectively. In the X2YZ Heusler, the Z main group element usually has a higher chemical affinity for X and Y. In this case, an ordered structure should be formed regardless of the choice of Z. The ternary Heusler compound that can be used is Mn3.1-x Co 1.1-y Sn, wherein X≤1.2 and Y≤1.0. The Heusler SAF structure may include a ternary Heusler compound as the first Heusler layer, the second Heusler layer, or both Heusler layers.

[0050] Also Mn 2.3 Sb is considered part of the L10 family of compounds, so the results discussed above suggest that a RuAl template spacer layer will also be effective in inducing SAF ordering between two L10 compounds whose constituent elements include a transition metal and a main group element. Other candidate L10 compounds include MnAl alloys, MnGa alloys, MnSn alloys, MnGe alloys, and FeAl alloys.

[0051] The structures described herein are suitable for various applications including MRAM elements and racetrack memory devices, such as those described in U.S. Patent 6,834,005, issued December 21, 2004, entitled "Shiftable magnetic shift register and method of using the same," which is incorporated herein by reference. One such MRAM element is Figure 11 As shown. As with the MRAM element, the tunnel barrier is located between two magnetic electrodes, one of which has a fixed magnetic moment and the other of which has a switchable magnetic moment, thereby allowing data to be recorded and erased. However, unlike the MRAM element of the prior art, Figure 11 The magnetic layer with a fixed magnetic moment (pinned layer) comprises Heusler layers separated by non-magnetic spacers (such as those described herein). For better performance, an optional (second) pinned layer may be advantageously employed.

[0052] As mentioned earlier, Figure 11 The template layer is a multilayer structure that is nonmagnetic at room temperature and includes alternating layers of Co and at least one other element E (preferably Al or Ga; or alloys of Al with Ga, Ge, Sn or any combination thereof (such as AlSn, AlGe, AlGa, AlGaGe, AlGaSn, AlGeSn and AlGaGeSn)). The composition of the structure is composed of Co 1-x E x, x is preferably in the range of 0.45 to 0.55 (close to a 1:1 ratio to promote the growth of alternating layers). At high Co concentrations, Co-E alloys are magnetic; furthermore, deviations from 1:1 can also make the growth of these structures difficult or impossible. An optional seed layer may be interposed between the substrate and the template layer. Overlying the template layer is a Heusler SAF structure comprising a first Heusler compound such as Mn3Ge, Mn3Sn, or Mn3Sb. Although these three binary Heusler compounds are mentioned for their ideal stoichiometric characterization (i.e., Mn3Z, where Z = Ge or Sn or Sb), their stoichiometry can vary within a limited range as described below. For Mn 3.1-x Ge and Mn 3.1-x For Sn, x can be in the range of 0 to 0.6; for Mn 3.1-x Sb, x may be in the range of 0 to 1.1. A spacer layer comprising both Ru and at least one other element E (having a 1-x E x The first Heusler layer is in contact with the second Heusler layer. A second Heusler layer, selected independently of the groups Mn3Ge, Mn3Sn, and Mn3Sb, is in contact with the spacer layer. The magnetic moments of the first and second Heusler layers are fixed and antiparallel to each other. An optional second pinning layer can be used to improve performance and can include Fe, a CoFe alloy, or Co2MnSi.

[0053] The tunnel barrier is preferably MgO(001), but other (001) oriented tunnel barriers such as CaO and LiF can be used. Alternatively, an insulator with a spinel structure (such as MgAl2O4) can be used as a tunnel barrier; its lattice spacing can be adjusted by controlling the Mg-Al ratio, which will result in a better lattice match with the Heusler compound (more preferably, the Mg-Al composition is Mg 1-z Al 2-z O4, where -0.5 < z < 0.5). For example, the switchable magnetic electrode covering the tunnel barrier may include Fe, a CoFe alloy, or a CoFeB alloy. The capping layer may include Mo, W, Ta, Ru, or a combination thereof. Current can be induced by applying a voltage between two magnetic electrodes separated by the tunnel barrier.

[0054] Some of the structures described herein can also be used in racetrack memory devices. In this case, the racetrack can be a nanowire comprising a substrate, an optional seeding layer, a template layer, and a first magnetic layer comprising two Heusler compounds separated by a nonmagnetic spacer layer. (For possible compositions of these layers, see above regarding Figure 11Note that in racetrack memory devices, there is usually no Figure 11 The tunnel barrier and switchable magnetic layer shown in ; however, in this case, Figure 11 The first magnetic layer shown in FIG will have a switchable, rather than fixed, magnetic moment. As described in U.S. Patent 6,834,005, magnetic domain walls can be moved along the racetrack. Data can be read from (and stored in) the racetrack by interrogating (or changing) the magnetic moment orientation of the magnetic material between adjacent domain walls within the racetrack.

[0055] The various layers described herein can be deposited by any one or more of a variety of methods, including magnetron sputtering, electrodeposition, ion beam sputtering, atomic layer deposition, chemical vapor deposition, and thermal evaporation.

[0056] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present invention is therefore indicated by the appended claims rather than by the foregoing description. All modifications that come within the meaning and range of equivalency of the claims are intended to be embraced within their scope.

Claims

1. A magnetic device comprising: A multi-layer structure comprising: a first layer comprising a first magnetic Heusler compound; A second layer that is nonmagnetic at room temperature, the second layer being as follows: contacting and covering the first layer; and comprising both Ru and Al, wherein the composition of the second layer is represented by Ru 1-x Al x , x is in the range of from 0.45 to 0.55, the thickness of the second layer is to to the extent that A third layer contacts and covers the second layer, the third layer comprising a second magnetic Heusler compound.

2. The device according to claim 1, wherein x ranges from 0.47 to 0.

53.

3. The device according to claim 1, wherein The magnetic moments of the first layer and the third layer are substantially perpendicular to an interface between the second layer and the first layer and an interface between the second layer and the third layer, respectively.

4. The device according to claim 1, wherein The thickness of each of the first layer and the third layer is less than 5 nm.

5. The device according to claim 1, wherein The magnetic moments of the first layer and the third layer are substantially antiparallel to each other.

6. The device according to claim 1, wherein The first magnetic Heusler compound and the second magnetic Heusler compound are independently selected from Mn 3.1-x Ge、Mn 3.1-x Sn and Mn 3.1-x Sb group, for Mn 3.1-x For Sb, x is in the range of 0 to 1.1, and for Mn 3.1-x Ge and Mn 3.1-x For Sn, x is in the range from 0 to 0.

6.

7. The device according to claim 1, wherein The first magnetic Heusler compound and / or the second magnetic Heusler compound is a ternary Heusler compound.

8. The device according to claim 7, wherein The ternary Heusler compound is Mn 3.1-x Co 1.1-y Sn, where x≤1.2, and y≤1.

0.

9. The device according to claim 1, wherein The magnetic moments of the first layer and the third layer are substantially parallel to an interface between the second layer and the first layer and an interface between the second layer and the third layer, respectively.

10. The device of claim 1, further comprising a tunnel barrier covering the multi-layer structure, thereby allowing current to pass through both the tunnel barrier and the multi-layer structure. The device of claim 10 , further comprising an additional magnetic layer in contact with the tunnel barrier.

12. The device according to claim 11, wherein The tunnel barrier is Mg 1-z Al 2-z O4, where -0.5<z<0.

5.

13. A magnetic device comprising: substrate; A multilayer structure covering the substrate, the multilayer structure comprising a first layer, a second layer and a third layer, wherein: The first layer includes a first magnetic Heusler compound, The second layer is non-magnetic at room temperature and includes Ru and Al. The composition of the second layer is expressed as Ru 1-x Al x , x is in the range of from 0.45 to 0.55, the thickness of the second layer is to within the scope of The third layer includes a second magnetic Heusler compound; a tunnel barrier covering the multilayer structure; and An additional magnetic layer is in contact with the tunnel barrier, wherein the additional magnetic layer has a switchable magnetic moment.

14. The device of claim 13, further comprising a capping layer in contact with the additional magnetic layer.

15. The device according to claim 13, wherein The first layer and / or the third layer includes Mn and an element selected from the group consisting of Sn, Sb, and Ge.

16. A magnetic device comprising: A multi-layer structure comprising a first layer, a second layer and a third layer, wherein: The first layer is magnetic and comprises a Heusler compound and / or an L10 compound, The second layer is non-magnetic at room temperature and includes Ru and Al. The composition of the second layer is expressed as Ru 1-x Al x , x is in the range of from 0.45 to 0.55, the thickness of the second layer is to within the scope of The third layer is magnetic and comprises a Heusler compound and / or an L10 compound.

17. The device according to claim 16, wherein The magnetic moments of the first layer and the third layer are substantially perpendicular to interfaces of the first layer and the third layer with the second layer.

18. The device according to claim 16, wherein The L10 compound is selected from the group consisting of MnGa, MnAl, FeAl, MnGe, MnSb and MnSn alloys.

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