Three-terminal design for spin accumulation magnetic sensor
View Patent ↗A spin accumulation sensor having a three terminal design that allows the free layer to be located at the air bearing surface. A non-magnetic conductive spin transport layer extends from a free layer structure (located at the ABS) to a reference layer structure removed from the ABS. The sensor includes a current or voltage source for applying a current across a reference layer structure. The current or voltage source has a lead that is connected with the non-magnetic spin transport layer and also to electric ground. Circuitry for measuring a signal voltage measures a voltage between a shield that is electrically connected with the free layer structure and the ground. The free layer structure can include a spin diffusion layer that ensures that all spin current is completely dissipated before reaching the lead to the voltage source, thereby preventing shunting of the spin current to the voltage source.
1. A spin accumulation sensor, comprising:
a non-magnetic spin transport conductive layer;
a reference layer structure located away from a free layer structure, the reference layer structure including a magnetic reference layer and a first thin contact layer, the first contact layer being located between the magnetic reference layer and the non-magnetic spin transport conductive layer;
wherein the free layer structure is located at the air bearing surface, the free layer structure including a magnetic free layer, a second contact layer and a spin diffusion layer, the contact layer being located between the free magnetic layer and the non-magnetic spin transport conductive layer;
first and second electrically conductive magnetic shields, the reference layer structure, free layer structure and nonmagnetic spin transport conductive layer being located between the first and second magnetic, electrically conductive shields; and
a current or voltage source electrically connected with the reference layer structure so as to apply an electric current through the reference layer structure resulting in a spin current in the non-magnetic spin transport conductive layer, the current or voltage source also being connected to a common electric ground connection, the connection with the common ground being made at a location that is separated from the reference layer structure by a distance that is at least one or more times the spin diffusion length of the spin-conductive layer; and
circuitry for measuring a signal voltage between a portion of the free layer structure and the common electric ground.
2. The spin accumulation sensor as in claim 1 wherein the spin diffusion layer is located between the magnetic free layer and the second electrically conductive magnetic shield, and wherein the spin diffusion layer comprises Pt, Ir or Re and has a spin diffusion length that is short enough to substantially mix the spins of current flowing through it.
3. The spin accumulation sensor as in claim 1 further comprising an electrically insulating layer sandwiched between the first electrically conductive magnetic shield and the non-magnetic spin transport conductive layer, and wherein the spin diffusion layer is sandwiched between the magnetic free layer and the second electrically conductive magnetic shield layer.
4. The spin accumulation sensor as in claim 1 further comprising a second electrically insulating layer between the magnetic reference layer and the second electrically conductive shield layer.
5. A spin accumulation sensor as in claim 1 wherein the current or voltage source includes a first lead electrically connected with the magnetic reference layer and a second lead electrically connected with the non-magnetic spin transport conductive layer and also with electric ground, and wherein the circuitry for measuring a signal voltage includes a first lead connected with the second electrically conductive magnetic shield and a second lead connected with the electric ground.
6. The spin accumulation sensor as in claim 5 wherein the second electrically conductive magnetic shield is electrically connected with the free layer structure.
7. The spin accumulation sensor as in claim 6 wherein the reference layer structure is electrically insulated from the second electrically conductive magnetic shield.
8. The spin accumulation sensor as in claim 1 wherein the first and second contact layers each comprise an metallic-like electrically conductive material.
9. The spin accumulation sensor as in claim 1 wherein the first and second contact layers each comprise a tunneling barrier material.
10. The spin accumulation sensor as in claim 1 wherein one of the first and second contact layers comprises a non-magnetic, metallic-like electrically conductive material and the other contact layer comprises a tunneling barrier material.
11. The spin accumulation sensor as in claim 1 wherein one of the first and second shields provides the common electric ground.
12. The spin accumulation sensor as in claim 1 where at least one of the first and second contact layers is a nano oxide layer, consisting of conducting pinholes in an insulating matrix.
13. The spin accumulation sensor as in claim 1 where the magnetic reference layer and the magnetic free layer each comprise Ni, Co, Fe or their alloys or a Heusler material, such as CoMnGe, CoMnSi, or layers of any of these materials.
14. The spin accumulation sensor as in claim 1 where the reference layer is wider in its planar dimension than the magnetic free layer.