Galvanomagnetic device and magnetic sensor

1. A galvanomagnetic device comprising:

a non-conductive substrate; a first magnetic layer formed on the non-conductive substrate and has a magnetic anisotropy perpendicular to the surface thereof; a second magnetic layer formed on the first magnetic layer; electrodes which pass a current through the first magnetic layer and the second magnetic layer in a first in-plane direction; and electrodes which detect an anomalous Hall voltage which occurs in a second in-plane direction perpendicular to the direction of the current;

wherein the anomalous Hall voltage and/or a magnetization reversal field of the first magnetic layer are configured according to a thickness of the first magnetic layer, a thickness of the second magnetic layer and a saturation magnetization of the second magnetic layer;

wherein the thickness of the first magnetic layer is between about 3 nanometers and about 5 nanometers, the thickness of the second magnetic layer is less than about 5 nanometers, and the saturation magnetization of the second magnetic layer is less than about 1000 kiloamperes per meter; and

wherein the saturation magnetization of the second magnetic layer is larger than a saturation magnetization of the first layer.

2. A galvanomagnetic device according to claim 1 wherein a saturation magnetization of the second magnetic layer is larger than a saturation magnetization of the first magnetic layer.

3. A galvanomagnetic device according to claim 1 wherein the second magnetic layer has magnetically anisotropic portions dispersed uniformly in all in-plane directions.

4. A galvanomagnetic device according to claim 1 wherein the anomalous Hall voltage occurs in the first magnetic layer.

5. A galvanomagnetic device according to claim 1 wherein the first magnetic layer is a rare earth/transition metal alloy thin film, and the second magnetic layer is an amorphous rare earth/transition metal alloy thin film.

6. A galvanomagnetic device according to claim 1 wherein the first magnetic layer comprises a Gd or another rare earth alloy thin film, a Co/Pt artificial lattice film, or a Co/Pd artificial lattice film.

7. A galvanomagnetic device according to claim 6 wherein the second magnetic layer comprises a FeCo alloy thin film, or a FeNi alloy thin film.

8. A galvanomagnetic device according to claim 1 wherein the first magnetic layer comprises a FeCoGd alloy thin film, and the second magnetic layer comprises a FeCoB alloy thin film.

9. A galvanomagnetic device according to claim 1 wherein in response to an externally applied magnetic field, the second magnetic layer reverses its magnetization and then the first magnetic layer reverses its magnetization, and wherein the second magnetic layer facilitates the reversal of magnetization of the first magnetic layer.

10. A magnetic sensor comprising:

a non-conductive substrate; a first magnetic layer formed on the non-conductive substrate and having a magnetic anisotropy perpendicular to the surface of the non-conductive substrate;

a second magnetic layer which is formed on the first magnetic layer;

electrodes which pass a current through the first magnetic layer and the second magnetic layer in a first in-plane direction; and

electrodes which detect an anomalous Hall voltage which occurs in a second in-plane direction perpendicular to the direction of the current;

wherein when the current is kept flowing between the current electrodes, the magnetization direction of the first magnetic layer magnetized by an external magnetic field, is detected as a signal by detecting an anomalous Hall voltage from the voltage electrodes;

wherein the anomalous Hall voltage and/or a magnetization reversal field of the first magnetic layer are configured according to a thickness of the first magnetic layer, a thickness of the second magnetic layer and a saturation magnetization of the second magnetic layer;

wherein the thickness of the first magnetic layer is between about 3 nanometers and about 5 nanometers, the thickness of the second magnetic layer is less than about 5 nanometers, and the saturation magnetization of the second magnetic layer is less than about 1000 kiloamperes per meter; and

wherein the saturation magnetization of the second magnetic layer is larger than a saturation magnetization of the first layer.

11. A magnetic sensor according to claim 10 wherein the anomalous Hall voltage occurs in the first magnetic layer.

12. A magnetic sensor according to claim 10 wherein the first magnetic layer is a rare earth/transition metal alloy thin film, and the second magnetic layer is an amorphous rare earth/transition metal alloy thin film.

13. A magnetic sensor according to claim 10 wherein the first magnetic layer comprises a Gd or another rare earth alloy thin film, a Co/Pt artificial lattice film, or a Co/Pd artificial lattice film.

14. A magnetic sensor according to claim 13 wherein the second magnetic layer comprises a FeCo alloy thin film, or a FeNi alloy thin film.

15. A magnetic sensor according to claim 10 wherein the first magnetic layer comprises a FeCoGd alloy thin film, and the second magnetic layer comprises a FeCoB alloy thin film.

16. A magnetic sensor comprising:

a non-conductive substrate;

a first magnetic layer formed on the non-conductive substrate and having a magnetic anisotropy perpendicular to the surface of the non-conductive substrate;

a second magnetic layer which is formed on the first magnetic layer; electrodes which pass a current through the first magnetic layer and the second magnetic layer in a first in-plane direction; and

electrodes which detect an anomalous Hall voltage which occurs in a second in-plane direction perpendicular to the direction of the current;

wherein when the current is kept flowing between the current electrodes, the magnetization direction of the first magnetic layer magnetized by an external magnetic field, is detected as a signal by detecting an anomalous Hall voltage from the voltage electrodes;

when the external magnetic field is negative, the first magnetic layer is magnetized downward and the Hall voltage derived therefrom is negative, and

if the polarity of the external magnetic field changes from negative to positive, magnetization of the first layer reverses and turns upward wherein the second magnetic layer facilitates the reversal of magnetization of the first magnetic layer, and the polarity of the anomalous Hall voltage derived from the first magnetic layer switches from positive to negative, and

if the external magnetic field changes from positive to negative, the magnetization of the first magnetic layer reverses and turns downward and the polarity of the anomalous Hall voltage becomes negative; and

wherein the anomalous Hall voltage and/or a magnetization reversal field of the first magnetic layer are dependent on a thickness of the first magnetic layer, a thickness of the second magnetic layer and a saturation magnetization of the second magnetic layer;

wherein the thickness of the first magnetic layer is between about 3 nanometers and about 5 nanometers, the thickness of the second magnetic layer is less than about 5 nanometers, and the saturation magnetization of the second magnetic layer is less than about 1000 kiloamperes per meter; and

wherein the saturation magnetization of the second magnetic layer is larger than a saturation magnetization of the first layer.