Magnetoresistive element having an adjustable magnetostriction and magnetic device comprising this magnetoresistive element

Abstract

A magnetoresistive element including: a storage layer having a first storage magnetostriction; a sense layer having a first sense magnetostriction; and a barrier layer between and in contact with the storage and sense layer. The magnetoresistive element also includes a compensating ferromagnetic layer having a second magnetostriction different from the first storage magnetostriction and/or sense magnetostriction, and adapted to compensate the first storage magnetostriction and/or the first sense magnetostriction so that a net magnetostriction of the storage layer and/or sense layer is adjustable between 10 ppm and +10 ppm or more negative than 10 ppm by adjusting a thickness of the compensating ferromagnetic layer. The present disclosure also concerns a magnetic device comprising the magnetoresistive element.

Claims

1. A magnetoresistive element comprising: a storage layer having a first storage magnetostriction; a sense layer having a first sense magnetostriction; a barrier layer between and in contact with the storage and sense layers; and a compensating ferromagnetic layer having a second magnetostriction different from the first storage magnetostriction and/or sense magnetostriction, wherein the thickness of the compensating ferromagnetic layer is such that the second magnetostriction of the compensating ferromagnetic layer compensates the first storage magnetostriction and/or the first sense magnetostriction, so that a net magnetostriction of the storage layer and/or sense layer is between 10 ppm and +10 ppm or more negative than 10 ppm, wherein the storage layer and/or sense layer is between the compensating ferromagnetic layer and the barrier layer, and wherein the magnetoresistive element further comprises a ferromagnetic coupling layer comprising a Fe or Co based alloy and adapted for providing an exchange coupling greater than 0.00005 N/m.

2. The magnetoresistive element according to claim 1, wherein the compensating ferromagnetic layer comprises a Ni or Co alloy containing less than 25% wt of Ta, Ti, Hf, Cr, Sc, Cu, Pt, Pd, Ag, Mo, Zr, W, Al, Si, Mg or combinations thereof, or comprises pure Ni or pure Co.

3. The magnetoresistive element according to claim 2, wherein the compensating ferromagnetic layer has a thickness between 0.5 nm and 10 nm.

4. The magnetoresistive element according to claim 1, further comprising a transition layer between the compensating ferromagnetic layer and at least one of the storage layer and the sense layer.

5. The magnetoresistive element according to claim 4, wherein the transition layer comprises Ti, Hf, Ta, Nb, Cr or combinations thereof, and/or has a thickness comprised between 0.1 nm and 1 nm.

6. The magnetoresistive element according to claim 1, further comprising a storage antiferromagnetic layer exchange coupling the storage layer, and wherein the ferromagnetic coupling layer is comprised between the storage antiferromagnetic layer and the compensating ferromagnetic layer.

7. The magnetoresistive element according to claim 1, comprising a transition layer between the compensating ferromagnetic layer and the ferromagnetic coupling layer.

8. The magnetoresistive element according to claim 1, wherein the storage layer comprises a SAF structure including a first ferromagnetic storage layer in contact with the barrier layer, a second ferromagnetic storage layer, and a SAF storage coupling layer between the first and second ferromagnetic storage layers; and wherein the compensating ferromagnetic layer is comprised between the SAF coupling layer and the first ferromagnetic storage layer and between the SAF coupling layer and the second ferromagnetic storage layer.

9. The magnetoresistive element according to claim 1, wherein the sense layer comprises a SAF structure including a first ferromagnetic sense layer in contact with the barrier layer), a second ferromagnetic sense layer, and a SAF coupling layer between the first and second ferromagnetic sense layers; and wherein the compensating ferromagnetic layer is comprised between the SAF coupling layer and the first ferromagnetic sense layer and between the SAF coupling layer and the second ferromagnetic sense layer.

10. The magnetoresistive element according to claim 8, further comprising a transition layer between the compensating ferromagnetic layer and at least one of the storage layer and the sense layer, wherein the transition layer is comprised between the compensating ferromagnetic layer and the first ferromagnetic storage layer and/or between the compensating ferromagnetic layer and the second ferromagnetic storage layer.

11. The magnetoresistive element according claim 9, further comprising a transition layer between the compensating ferromagnetic layer and at least one of the storage layer and the sense layer, wherein the transition layer is comprised between the compensating ferromagnetic layer and the first ferromagnetic sense layer and/or between the compensating ferromagnetic layer and the second ferromagnetic sense layer.

12. The magnetoresistive element according to claim 8, further comprising a storage antiferromagnetic layer exchange coupling the storage layer, wherein the ferromagnetic coupling layer is comprised between the storage antiferromagnetic layer and the compensating ferromagnetic layer, and wherein the ferromagnetic coupling layer is comprised between the SAF storage coupling layer and the compensating ferromagnetic layer.

13. The magnetoresistive element according to claim 9, further comprising a storage antiferromagnetic layer exchange coupling the storage layer, wherein the ferromagnetic coupling layer is comprised between the storage antiferromagnetic layer and the compensating ferromagnetic layer, and wherein another ferromagnetic coupling layer is comprised between the SAF sense coupling layer and the compensating ferromagnetic layer.

14. The magnetoresistive element according to claim 12, further comprising a transition layer between the compensating ferromagnetic layer and at least one of the storage layer and the sense layer, wherein another transition layer is comprised between the ferromagnetic coupling layer and the compensating ferromagnetic layer.

15. A magnetic device comprising: a magnetoresistive element comprising: a storage layer having a first storage magnetostriction; a sense layer having a first sense magnetostriction; a barrier layer between and in contact with the storage and sense layers; and a compensating ferromagnetic layer having a second magnetostriction different from the first storage magnetostriction and/or sense magnetostriction, wherein the thickness of the compensating ferromagnetic layer is such that the second magnetostriction of the compensating ferromagnetic layer compensates the first storage magnetostriction and/or the first sense magnetostriction, so that a net magnetostriction of the storage layer and/or sense layer is between 10 ppm and +10 ppm or more negative than 10 ppm, wherein the storage layer and/or sense layer is between the compensating ferromagnetic layer and the barrier layer, and wherein the magnetoresistive element further comprises a ferromagnetic coupling layer comprising a Fe or Co based alloy and adapted for providing an exchange coupling greater than 0.00005 N/m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which:

(2) FIG. 1 represents a magnetoresistive element, according to an embodiment;

(3) FIG. 2 illustrates a the magnetoresistive element, according to another embodiment;

(4) FIG. 3 shows the magnetoresistive element comprising a sense layer having a SAF structure, according to an embodiment;

(5) FIG. 4 shows the magnetoresistive element of FIG. 3, according to another embodiment;

(6) FIG. 5 represents the magnetoresistive element according to another embodiment wherein the storage layer comprises a SAF structure, according to an embodiment;

(7) FIG. 6 illustrates a magnetoresistive element wherein both the storage layer and the sense layer comprise a SAF structure; and

(8) FIG. 7 represents the evolution of a net magnetostriction of a portion of the magnetoresistive element.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS

(9) FIG. 1 represents a magnetoresistive element 1 according to an embodiment. The magnetoresistive element comprises a storage, or reference, layer 21 having a first storage magnetostriction .sub.R1, a sense layer 23 having a first sense magnetostriction .sub.S1, and a barrier layer 22 between and in contact with the storage and sense layer 21, 23.

(10) Each of the storage layer 21 and the sense layer 23 includes, or is formed of, a magnetic material and, in particular, a magnetic material of the ferromagnetic type. A ferromagnetic material can be characterized by a substantially planar magnetization with a particular coercivity, which is indicative of a magnitude of a magnetic field to reverse the magnetization after it is driven to saturation in one direction. In general, storage layer 21 and the sense layer 23 can include the same ferromagnetic material or different ferromagnetic materials. Suitable ferromagnetic materials include transition metals, rare earth elements, and their alloys, either with or without main group elements. For example, suitable ferromagnetic materials include iron (Fe), cobalt (Co), nickel (Ni), and their alloys, such as permalloy (or Ni80Fe20); alloys based on Ni, Fe, and boron (B); Co90Fe10; and alloys based on Co, Fe, and B. In some instances, alloys based on Ni and Fe (and optionally B) can have a smaller coercivity than alloys based on Co and Fe (and optionally B).

(11) Preferably, the storage layer 21 and/or the sense layer 23 comprises a Fe based alloy providing a TMR ratio greater than 20%.

(12) The storage layer 21 can include a hard ferromagnetic material, namely one having a relatively high coercivity, such as greater than about 50 Oe. The sense layer 23 can include a soft ferromagnetic material, namely one having a relatively low coercivity, such as no greater than about 50 Oe. In such manner, a magnetization of the sense layer 23 can be readily varied under low-intensity magnetic fields during read operations, while a magnetization of the storage, or reference, layer 21 remains stable.

(13) A thickness of each of the storage layer 21 and the sense layer 23 can be in the nanometer (nm) range, such as from about 0.5 nm to about 10 nm. A thickness of each of the storage layer 21 and the sense layer 23 is preferably from about 0.5 nm to about 5 nm and more and preferably between 1 nm and 2.5 nm.

(14) The barrier layer 22 includes, or is formed of, an insulating material. Suitable insulating materials include oxides, such as aluminum oxide (e.g., Al.sub.2O.sub.3) and magnesium oxide (e.g., MgO). A thickness of the barrier layer 22 can be in the nm range, such as from about 0.5 nm to about 10 nm.

(15) The magnetoresistive element 1 further comprises a compensating ferromagnetic layer 25 included between an electrode 28 and the sense layer 23, such that the sense layer 23 is between the compensating ferromagnetic layer 25 and the barrier layer 22 with which it is in contact. The compensating ferromagnetic layer 25 has a second magnetostriction .sub.2, different from the first sense magnetostriction .sub.S1. The compensating ferromagnetic layer 25 is adapted to compensate the first sense magnetostriction .sub.S1.

(16) The compensating ferromagnetic layer 25 can comprise a Ni or Co alloy containing less than 25% wt of Ta, Ti, Hf, Cr, Sc, Cu, Pt, Pd, Ag, Mo, Zr, W, Al, Si, Mg or any combinations of these elements. The compensating ferromagnetic layer 25 can also comprise pure Ni or pure Co. Here, pure Ni and pure Co can mean at least 99.9% wt Ni and at least 99.9% Co, respectively. The compensating ferromagnetic layer 25 has a thickness being typically between 0.5 nm and 10 nm.

(17) The net magnetostriction .sub.net of the sense layer 23 can be adjusted between 10 ppm et +10 ppm or to a more negative magnetostriction than 10 ppm by adjusting a thickness of the compensating ferromagnetic layer 25.

(18) FIG. 2 illustrates a variant of the magnetoresistive element 1 where the compensating ferromagnetic layer 25 is included on the other side of the barrier layer 22 such that the storage layer 21 is between the compensating ferromagnetic layer 25 and the barrier layer 22 with which it is in contact. The second magnetostriction .sub.2 of the compensating ferromagnetic layer 25 differs from the first storage magnetostriction .sub.R1 and the compensating ferromagnetic layer 25 is adapted to compensate the first storage magnetostriction .sub.R1.

(19) In fact, the net magnetostriction .sub.net of the storage and/or sense layer 21, 23 can be adjusted between 10 ppm et +10 ppm or to a more negative magnetostriction than 10 ppm by adjusting the thickness of the compensating ferromagnetic layer 25 and/or the thickness of the storage and/or sense layer 21, 23.

(20) Preferably, the second magnetostriction .sub.2 of the compensating ferromagnetic layer 25 is negative and the first storage and sense magnetostriction .sub.R1, .sub.S1 is positive.

(21) Adjusting the thickness of the compensating ferromagnetic layer 25 such that the net magnetostriction .sub.net is negative (more negative than 10 ppm) results in providing an stress-induced magnetic anisotropy on at least one of the sense layer 23 and the storage layer 21 and provide a stress-induced magnetic anisotropy, as described in yet unpublished European patent application number EP20150290013 by the present applicant.

(22) In order to allow a structural transition between the layers having a negative magnetostriction (the compensating ferromagnetic layer 25) and the layers having a positive magnetostriction (the storage and/or sense layer 21, 23), a transition layer 26 can be included between the layers having a negative magnetostriction and the layers having a positive magnetostriction. The transition layer 26 can comprise Ti, Hf, Ta, Nb, Cr or any combinations of these elements. The transition layer 26 should be thin enough so that a magnetic coupling still exists between the layers having a negative magnetostriction and the layers having a positive magnetostriction. Preferably, the transition layer 26 has a thickness comprised between 0.1 nm and 1 nm.

(23) In the embodiment of FIG. 1, a transition layer 26 is included between compensating ferromagnetic layer 25 and the sense layer 23. In the embodiment of FIG. 2, the magnetoresistive element 1 comprises a transition layer 26 included between compensating ferromagnetic layer 25 and the storage layer 21.

(24) As illustrated in FIG. 2, the magnetoresistive element 1 can comprise a storage antiferromagnetic layer 24 magnetically exchange coupling the storage (or reference) layer 21 such as to pin the magnetization of the storage layer 21. In an embodiment, a ferromagnetic coupling layer 27 is included between the antiferromagnetic layer 24 and the compensating ferromagnetic layer 25. The ferromagnetic coupling layer 27 can comprise a Fe or Co based alloy and have a thickness between 0.2 nm and 5 nm and preferably between 0.5 nm and 1.5 nm.

(25) The ferromagnetic coupling layer 27 is adapted for providing a magnetic exchange coupling greater than 0.05 erg/cm.sup.2. For example, the ferromagnetic coupling layer 27 can provide an exchange coupling that is greater than 0.05 erg/cm.sup.2 between the storage antiferromagnetic layer 24 and the storage layer 21.

(26) A transition layer 26 can further be included between the compensating ferromagnetic layer 25 and the ferromagnetic coupling layer 27.

(27) FIG. 3 shows the magnetoresistive element according to another embodiment wherein the sense layer comprises a SAF structure including a first ferromagnetic sense layer 231 in contact with the barrier layer 22, a second ferromagnetic sense layer 232, and a SAF sense coupling layer 233 between the first and second ferromagnetic sense layers 231, 232. A compensating ferromagnetic layer 25 is included between the SAF sense coupling layer 233 and the first ferromagnetic sense layer 231. Another compensating ferromagnetic layer 25 is included between the SAF sense coupling layer 233 and the second ferromagnetic sense layer 232.

(28) A transition layer 26 can be inserted between the compensating ferromagnetic layer 25 and the first ferromagnetic sense layer 231 and/or between the compensating ferromagnetic layer 25 and the second ferromagnetic sense layer 232.

(29) FIG. 4 shows the magnetoresistive element of FIG. 3, according to another embodiment. In the configuration of FIG. 4, the magnetoresistive element 1 comprises a ferromagnetic coupling layer 27 between the SAF sense coupling layer 233 and each of the compensating ferromagnetic layers 25. The ferromagnetic coupling layer 27 enhances the RKKY-type magnetic exchange coupling between the first ferromagnetic sense layer 231 and of the second ferromagnetic sense layer 232 to a value above 0.05 erg/cm.sup.3.

(30) A transition layer 26 can be included between the ferromagnetic coupling layer 27 and each of the compensating ferromagnetic layers 25.

(31) FIG. 5 shows the magnetoresistive element according to another embodiment wherein the storage layer comprises a SAF structure including a first ferromagnetic storage layer 211 in contact with the barrier layer 22, a second ferromagnetic storage layer 212, and a SAF storage coupling layer 213 between the first and second ferromagnetic storage layers 211, 212. A compensating ferromagnetic layer 25 is included between the SAF storage coupling layer 213 and the first ferromagnetic storage layer 211. Another compensating ferromagnetic layer 25 is included between the SAF storage coupling layer 213 and the second ferromagnetic storage layer 212.

(32) A transition layer 26 can be inserted between the compensating ferromagnetic layer 25 and the first ferromagnetic storage layer 211 and/or between the compensating ferromagnetic layer 25 and the second ferromagnetic storage layer 212.

(33) A ferromagnetic coupling layer 27 can be included between the SAF storage coupling layer 213 and each of the compensating ferromagnetic layers 25. The ferromagnetic coupling layer 27 enhances the RKKY-type magnetic exchange coupling between the first ferromagnetic storage layer 211 and of the second ferromagnetic storage layer 212 to a value above 0.05 erg/cm.sup.3.

(34) A transition layer 26 can be included between the ferromagnetic coupling layer 27 and each of the compensating ferromagnetic layers 25.

(35) FIG. 6 illustrates a magnetoresistive element 1 wherein both the storage layer 21 and the sense layer 23 comprise a SAF structure, such that the magnetoresistive element 1 corresponds to a combination of the SAF sense structure of FIG. 4 and of the SAF storage structure of FIG. 5.

(36) FIG. 7 represents the evolution of the net magnetostriction .sub.net of a portion of the magnetoresistive element comprising the sequence of layers Ta/Ni/Ta0.3/CoFeB1.5/MgO (corresponding to the sequence: electrode 28, compensating ferromagnetic layers 25, transition layer 26, sense layer 23 and barrier layer 22. The net magnetostriction .sub.net continuously decreases as a function of the thickness of the compensating ferromagnetic layers 25 comprising Ni. The net magnetostriction .sub.net can be cancelled when the thickness of the compensating ferromagnetic layers 25 is about 2.3 nm.

REFERENCE NUMBERS AND SYMBOLS

(37) 1 magnetoresitive element 21 storage layer 211 first ferromagnetic storage layer 212 second ferromagnetic storage layer 213 SAF storage coupling layer 22 barrier layer 23 sense layer 231 first ferromagnetic sense layer 232 second ferromagnetic sense layer 233 SAF sense coupling layer 24 storage antiferromagnetic layer 25 compensating ferromagnetic layer 26 transition layer 27 ferromagnetic coupling layer 28 electrode .sub.R1 first storage magnetostriction .sub.S1 first sense magnetostriction .sub.2 second magnetostriction .sub.net net magnetostriction