Tunneling magnetoresistive (TMR) read head with low magnetic noise
View Patent ↗A tunneling magnetoresistance (TMR) device, like a TMR read head for a magnetic recording disk drive, has low magnetic damping, and thus low mag-noise, as a result of the addition of a ferromagnetic backing layer to the ferromagnetic free layer. The backing layer is a material with a low Gilbert damping constant or parameter α, the well-known dimensionless coefficient in the Landau-Lifshitz-Gilbert equation. The backing layer may have a thickness such that it contributes up to two-thirds of the total moment/area of the combined free layer and backing layer. The backing layer may be formed of a material having a composition selected from (Co x Fe (100-x) ) (100-y) X y , (Co 2 Mn) (100-y) X y and (Co 2 Fe x Mn (1-x) ) (100-y) X y , where X is selected from Ge, Al and Si, and (Co 2 Fe) (100-y) Al y , where y is in a range that results in a low damping constant for the material.
1. A tunneling magnetoresistive (TMR) device comprising:
a substrate;
a pinned ferromagnetic layer having an in-plane magnetization direction;
a free ferromagnetic layer having an in-plane magnetization direction substantially free to rotate in the presence of an external magnetic field; and
an electrically insulating tunneling barrier layer between the pinned ferromagnetic layer and the free ferromagnetic layer;
wherein the free ferromagnetic layer comprises a first ferromagnetic layer comprising an alloy of one or more of Co, Fe, Ni and B and a ferromagnetic backing layer, the first ferromagnetic layer being between the tunneling barrier layer and the backing layer and the backing layer having a thickness whereby the magnetic moment per unit area of the backing layer is less than two-thirds the total magnetic moment per unit area of the free ferromagnetic layer; and
wherein the backing layer comprises a ferromagnetic material selected from the group consisting of (CO x Fe (100-x) ) (100-y) Ge y where the subscripts represent atomic percent, x is equal to or greater than 45 and less than or equal to 55, and y is equal to or greater than 5 and less than or equal to 33; (Co 2 Mn) (100-y) Ge y where the subscripts represent atomic percent, and y is equal to or greater than 25 and less than or equal to 33; (Co 2 Mn) (100-y) Si y where the subscripts represent atomic percent, and y is equal to or greater than 25 and less than or equal to 33; (Co 2 Fe x n (1-x) )Ge where x is equal to or greater than 0.2 and less than or equal to 0.5; and (Co 2 Fe x n (1-x) )Si where x is equal to or greater than 0.2 and less than or equal to 0.5.
2. The device of claim 1 wherein the backing layer ferromagnetic material is (Co x Fe (100-x) ) (100-y) Ge y and y is equal to or greater than 20 and less than or equal to 30.
3. The device of claim 1 wherein the free ferromagnetic layer has a magnetic moment per unit area equivalent to the moment per unit area of a Ni 80 Fe 20 layer having a thickness of at least 40Å.
4. The device of claim 1 wherein the first free ferromagnetic layer is an alloy comprising Co, Fe and B and the tunneling barrier layer consists essentially of MgO.
5. The device of claim 1 further comprising a diffusion prevention located between and in contact with the first free ferromagnetic layer and the backing layer.
6. The device of claim 1 wherein the pinned ferromagnetic layer is formed of a ferromagnetic material other than the material of the backing layer.
7. The device of claim 1 wherein the pinned layer is located between the substrate and the free ferromagnetic layer.
8. The device of claim 1 wherein the free ferromagnetic layer is located between the substrate and the pinned layer.
9. The device of claim 1 wherein the pinned layer is an antiparallel (AP) pinned structure comprising a first AP-pinned (AP 1 ) ferromagnetic layer having an in-plane magnetization direction, a second AP-pinned (AP 2 ) ferromagnetic layer adjacent the tunneling barrier layer and having an in-plane magnetization direction substantially antiparallel to the magnetization direction of the AP 1 layer, and an AP coupling (APC) layer between and in contact with the AP 1 and AP 2 layers.
10. The device of claim 9 wherein the AP-pinned structure is a self-pinned structure.
11. The device of claim 9 further comprising an antiferromagnetic layer exchange-coupled to the AP 1 layer for pinning the magnetization direction of the AP 1 layer.
12. The device of claim 9 further comprising a hard magnetic layer in contact with the AP 1 layer for pinning the magnetization direction of the AP 1 layer.
13. The device of claim 1 wherein the device is a magnetoresistive read head for reading magnetically recorded data from tracks on a magnetic recording medium, and wherein the substrate is a first shield formed of magnetically permeable material.