Magnetic recording head having a sensor stack disposed along a stripe-height direction

1 . A magnetic recording head having an air-bearing surface, wherein the magnetic recording head comprises a reader having at least one sensor stack, wherein the at least one sensor stack comprises:

a free layer having an air-bearing-surface side and a side opposite to the air-bearing surface side, wherein the free layer has a magnetization direction that is free to rotate in response to an external magnetic field associated with recorded data on a magnetic storage medium; and

at least one reference layer disposed above the side opposite the air-bearing surface side in a stripe-height direction, wherein the reference layer has a magnetization direction that is substantially fixed against rotation in response to the external magnetic field associated with recorded data on the magnetic storage medium, wherein the at least one reference layer has a first side and a second side opposite to the first side, wherein the first side faces the side opposite to the air-bearing surface side of the free layer, and wherein the at least one sensor stack is disposed along a stripe-height direction from the free layer.

2 . The magnetic recording head of claim 1 , wherein the at least one reference layer has a thickness in the stripe-height direction from 1 to 6 nanometers.

3 . The magnetic recording head of claim 1 , wherein the at least one reference layer has a width in a cross-track direction from 6 to 30 nanometers.

4 . The magnetic recording head of claim 1 , wherein the at least one reference layer has a length in a down-track direction from 4 to 15 nanometers.

5 . The magnetic recording head of claim 1 , wherein the at least one reference layer comprises at least one ferromagnetic material chosen from a cobalt-iron alloy, a cobalt-iron-boron alloy, a nickel-iron permalloy, and combinations thereof.

6 . The magnetic recording head of claim 1 , further comprising a spacer layer between the free layer and the at least one reference layer, wherein the spacer layer has a thickness in the stripe-height direction of 5 nanometers or less.

7 . The magnetic recording head of claim 6 , wherein the spacer layer between the free layer and the at least one reference layer comprises a tunnel barrier layer having a thickness in the stripe-height direction from 0.1 to 2 nanometers.

8 . The magnetic recording head of claim 7 , wherein the tunnel barrier layer comprises magnesium oxide.

9 . The magnetic recording head of claim 1 , wherein the at least one reference layer is part of a synthetic antiferromagnetic structure, wherein the synthetic antiferromagnetic structure comprises:

a pinned layer disposed above the at least one reference layer in the stripe-height direction; and

a separation layer disposed between the pinned layer and the at least one reference layer.

10 . The magnetic recording head of claim 9 , further comprising an antiferromagnetic layer disposed above the pinned layer in the stripe-height direction.

11 . The magnetic recording head of claim 1 , further comprising an antiferromagnetic layer disposed above the at least one reference layer in the stripe-height direction.

12 . The magnetic recording head of claim 1 , further comprising:

a first side shield disposed in a cross-track direction from the free layer; and

a second side shield disposed in an opposite cross-track direction from the free layer and the first side shield, wherein the first side shield and the second side shield each have a magnetic moment that produce a magnetic field that biases a magnetic moment of the free layer.

13 . The magnetic recording head of claim 1 , wherein the at least one sensor stack is a first sensor stack, and further comprising:

a top shield disposed in a down-track direction from the free layer;

a bottom shield disposed in an opposite down-track direction from the free layer and the top shield; and

a second sensor stack disposed along the opposite down-track direction from the free layer, wherein the second sensor stack comprises:

the free layer; and

a second reference layer disposed between the free layer and the bottom shield.

14 . The magnetic recording head of claim 13 , wherein the first sensor stack comprises:

a first electrode in electrical communication with the free layer;

a second electrode in electrical communication with first sensor stack so that a current flows through the first sensor stack when a voltage is applied across the first electrode and the second electrode, and wherein the second sensor stack comprises:

the first electrode; and

a third electrode in electrical communication with the second sensor stack so that a current flows through the second sensor stack when a voltage is applied across the first electrode and the third electrode.

15 . The magnetic recording head of claim 14 , wherein the second reference layer is part of a synthetic antiferromagnetic structure, wherein the synthetic antiferromagnetic structure comprises:

a pinned layer disposed in the opposite down-track direction from the second reference layer; and

a separation layer disposed between the pinned layer and the second reference layer.

16 . The magnetic recording head of claim 15 , further comprising an antiferromagnetic layer disposed in the opposite down-track direction from the pinned layer, wherein the antiferromagnetic layer disposed is disposed between the pinned layer and the bottom shield.

17 . A data storage device comprising:

the magnetic recording head of claim 1 ;

a magnetic storage medium configured to store data in a plurality of data tracks, wherein each data track comprises a plurality of bits of data, and wherein each bit has an associated magnetic field;

a controller operably connected to the magnetic recording head and configured to control operations of the data storage device;

a memory operably connected to the controller, the memory storing program instructions; and

the program instructions, when executed by the controller, cause the controller to:

apply current through the at least one sensor stack of the magnetic recording head;

detect a change in resistance in the at least one sensor stack in response to a magnetic field of the magnetic storage medium; and

process the change in resistance in the at least one sensor stack into data.

18 . A method comprising:

applying a current through a sensor stack of a reader in a magnetic recording head having an air-bearing surface, wherein the sensor stack comprises:

a free layer having an air-bearing surface side and a side opposite to the air-bearing surface side, wherein the free layer has a magnetization direction that is free to rotate in response to an external magnetic field associated with recorded data on a magnetic storage medium; and

at least one reference layer disposed above the side opposite the air-bearing surface side in a stripe-height direction, wherein the reference layer has a magnetization direction that is substantially fixed against rotation in response to the external magnetic field associated with recorded data on the magnetic storage medium, wherein the at least one reference layer has a first side and a second side opposite to the first side, wherein the first side faces the side opposite to the air-bearing surface side of the free layer, and wherein applying the current occurs while the magnetic recording head is positioned adjacent to a data track of the magnetic storage medium that is rotating;

detecting a change in resistance in the sensor stack in response to a magnetic field of the magnetic storage medium; and

processing the change in resistance in the sensor stack into data.

19 . The method of claim 18 , wherein processing the change in resistance comprises:

converting the change in resistance into an electrical signal proportional to the magnetic field; and

processing the electrical signal into data.

20 . The method of claim 18 , wherein the sensor stack is a first sensor stack, wherein the magnetic recording head further comprises:

a top shield disposed in a down-track direction from the free layer;

a bottom shield disposed in an opposite down-track direction from the free layer and the top shield;

a second sensor stack comprising a second reference layer disposed in the opposite down-track direction from the free layer, wherein the second reference layer is disposed between the free layer and the bottom shield, and wherein the method further comprises:

applying a current through a second sensor stack of the reader, wherein the second sensor stack comprises the second reference layer, wherein applying the current occurs while the magnetic recording head is positioned adjacent to the data track of a magnetic storage medium that is rotating; and

detecting a change in resistance in the second sensor stack in response to a magnetic field of the magnetic storage medium;

processing the change in resistance in the second sensor stack into data.