Depolarizing layer in a magnetic stack

1. An apparatus comprising a magnetic stack positioned on an air bearing surface (ABS) and contacting a spin depolarizing layer that is a minority spin current carrier, the spin depolarizing layer configured with a thickness and spin diffusion length corresponding to a net zero spin polarization at an interface of the magnetic stack and spin depolarizing layer.

2. The apparatus of claim 1 , wherein the magnetic stack comprises a fixed magnetization layer separated from a free magnetization layer by a non-magnetic layer.

3. The apparatus of claim 1 , wherein the magnetic stack comprises a first free magnetic layer separated from a second free magnetic layer by a non-magnetic layer, the magnetic stack not having a fixed magnetization.

4. The apparatus of claim 1 , wherein the spin depolarizing layer comprises a nickel alloy.

5. The apparatus of claim 4 , wherein the nickel alloy is NiCr, NiV, NiFeCr, or NiFeV.

6. The apparatus of claim 1 , wherein the spin depolarizing layer is magnetic and does not add to a shield-to-shield spacing of the magnetic stack.

7. The apparatus of claim 1 , wherein the spin diffusion length is less than or equal to 5 nm.

8. The apparatus of claim 1 , wherein the thickness is greater than the spin diffusion length.

9. A data reader comprising separate detector and injector magnetic stacks sharing a common spin accumulation layer, the detector stack positioned on an air bearing surface (ABS) and the injector stack positioned distal the ABS, the detector stack contacting a first spin depolarizing layer that is a minority spin current carrier, the first spin depolarizing layer having a thickness and spin diffusion length corresponding to a net zero spin polarization at an interface of the common spin accumulation layer and first spin depolarizing layer.

10. The data reader of claim 9 , wherein the first spin depolarizing layer is part of a synthetic antiferromagnet (SAF) and is separated from a ferromagnetic layer by a non-magnetic layer.

11. The data reader of claim 10 , wherein the first depolarizing and ferromagnetic layers have different thicknesses as measured parallel to the ABS.

12. The data reader of claim 10 , wherein the first depolarizing and ferromagnetic layers have different fixed magnetization orientations.

13. The data reader of claim 10 , wherein the ferromagnetic layer is a majority spin current carrier.

14. The data reader of claim 9 , wherein a second spin depolarizing layer is disposed between a magnetically free layer of the detector stack and a magnetic shield.

15. The data reader of claim 14 , wherein the first and second spin depolarizing layers have dissimilar thicknesses as measured parallel to the ABS.

16. The data reader of claim 9 , wherein the injector stack comprises a polarizing ferromagnetic layer contacting the common spin accumulation layer.

17. The data reader of claim 9 , wherein the injector stack comprises a spin Hall effect layer contacting the common spin accumulation layer.

18. The data reader of claim 9 , wherein the spin accumulation layer has a smaller thickness than the first spin depolarizing layer.

19. A method comprising:

positioning a magnetic stack on an air bearing surface (ABS) contacting a spin depolarizing layer that is a minority spin current carrier;

tuning the spin depolarizing layer to have a thickness and spin diffusion length corresponding to a net zero spin polarization at an interface of the magnetic stack and spin depolarizing layer; and

passing a sensing current through the spin depolarizing layer to depolarize the sensing current.

20. The method of claim 19 , wherein the sensing current reaches the spin depolarizing layer with a polarized magnetization orientation.