Magnetoresistive element for a 2D magnetic sensor having a reduced hysteresis response
A magnetoresistive element for a 2D magnetic sensor, the magnetoresistive element including a tunnel barrier layer included between a reference layer having a reference magnetization and a sense layer having a sense magnetization. The sense layer includes a sense synthetic antiferromagnetic structure including a first sense sublayer in contact with the tunnel barrier layer and separated from a second sense sublayer by a first non-magnetic spacer layer such that the first sense sublayer is antiferromagnetically coupled to the second sense sublayer. The sense layer is configured such that a sense magnetic ratio ΔM defined as: Δ M = M s F M 2 t F M 2 - M s F M 1 t F M 1 M s F M 2 t F M 2 + M s F M 1 t F M 1 wherein M SFM1 and M SFM2 are the spontaneous magnetizations of the first and second sense sublayers and t FM1 and t FM2 are the thicknesses of the first and second sense sublayers; and wherein the sense magnetic ratio is between 0.1 and 0.25.
1. A magnetoresistive element for a 2D magnetic sensor, the magnetoresistive element comprising a tunnel barrier layer included between a reference layer having a reference magnetization and a sense layer having a sense magnetization;
wherein the sense layer comprises a synthetic antiferromagnetic (SAF) structure including a ferromagnetic first sense sublayer in contact with the tunnel barrier layer and separated from a ferromagnetic second sense sublayer by a first non-magnetic spacer layer such that the first sense sublayer is antiferromagnetically coupled to the second sense sublayer;
wherein the sense layer is configured such that a sense magnetic ratio ΔM is defined as:
Δ
M
=
M
s
F
M
2
t
F
M
2
-
M
s
F
M
1
t
F
M
1
M
s
F
M
2
t
F
M
2
+
M
s
F
M
1
t
F
M
1
wherein M SFM1 and M SFM2 are the spontaneous magnetizations of, respectively, the first and second sense sublayers and t FM1 and t FM2 are the thicknesses of, respectively, the first and second sense sublayers;
wherein the sense magnetic ratio ΔM is between 0.1 and 0.25; and
wherein the second sense sublayer comprises a spontaneous magnetization that increases with increasing distance from the sense spacer layer.
2. The magnetoresistive element according to claim 1 , wherein the first sense sublayer has a thickness between 1 nm and 3 nm and the second sense sublayer has a thickness between 2 nm and 6 nm.
3. The magnetoresistive element according to claim 2 , wherein the second sense sublayer has a greater thickness than the first sense sublayer.
4. The magnetoresistive element according to claim 3 , wherein the first sense sublayer comprises nonmagnetic elements in order to decrease its spontaneous magnetization.
5. The magnetoresistive element according to claim 1 , wherein the sense spacer layer comprises Ru, W, Mo or Ir or a combination of these elements.
6. The magnetoresistive element according to claim 1 , wherein the second sense sublayer comprises a ferromagnetic material containing nonmagnetic impurities in a concentration that decreases with increasing distance from the sense spacer layer.
7. The magnetoresistive element according to claim 1 ,
wherein the second sense sublayer comprises a plurality of ferromagnetic sense bi-layers, each sense bi-layer including a low spontaneous sense layer and a high spontaneous sense layer having a spontaneous magnetization higher than the one of the low spontaneous sense layer; and
wherein the thicknesses of the low spontaneous sense layer relative to the thicknesses of the high spontaneous sense layer decreases with increasing distance from the sense spacer layer.
8. The magnetoresistive element according to claim 1 ,
wherein the second sense sublayer comprises a proximal second sense sublayer proximal the first sense spacer layer and a distal second sense sublayer distal the first sense spacer layer and ferromagnetically coupled to the proximal second sense sublayer; and
wherein the distal second sense sublayer has a spontaneous magnetization that is at least two times greater than the proximal second sense sublayer.
9. The magnetoresistive element according to claim 8 , wherein the proximal second sense sublayer comprises a ferromagnetic material containing nonmagnetic impurities decreasing the spontaneous magnetization of the ferromagnetic material.
10. The magnetoresistive element according to claim 1 , wherein the second sense sublayer comprises a proximal second sense sublayer proximal the first sense spacer layer and a distal second sense sublayer distal the first sense spacer layer, the proximal second sense sublayer being separated from the distal second sense sublayer by a non-magnetic second sense spacer layer and antiferromagnetically coupled to the distal second sense sublayer.
11. The magnetoresistive element according to claim 10 , wherein the spontaneous magnetization of the distal second sense sublayer is higher than the spontaneous magnetization of the first sense layer and the proximal second sense sublayer.
12. The magnetoresistive element according to claim 10 , comprising a plurality of the sense SAF structures.
13. The magnetoresistive element according to claim 1 , wherein the sense layer further comprises an intermediate ferromagnetic sense layer on each side of the sense spacer layer and in contact with the sense spacer layer.
14. A 2D magnetic sensor comprising a plurality of the magnetoresistive elements according to claim 1 .