Magnetoresistive element and manufacturing method thereof

1. A magnetoresistive element comprising:

a first stacked structure formed by sequentially stacking a first fixed layer in which a magnetization direction is fixed and a first nonmagnetic layer;

a second stacked structure formed on the first stacked structure by sequentially stacking a free layer in which a magnetization direction is changeable, a second nonmagnetic layer, and a second fixed layer in which a magnetization direction is fixed; and

a circumferential wall formed in contact with a circumferential surface of the second stacked structure to surround the second stacked structure, and made of an insulator,

wherein a circumferential surface of the first stacked structure is substantially perpendicular, and

the second stacked structure has a tapered shape which narrows upward.

2. The element according to claim 1 , wherein an area of a bottom surface of the second stacked structure is smaller than that of an upper surface of the first stacked structure.

3. The element according to claim 1 , wherein letting t 1 be a film thickness of the second stacked structure, t 2 be a film thickness of the circumferential wall, and θ 1 be a taper angle, a relationship indicated by

t 2> t 1/tan θ1

is met.

4. The element according to claim 3 , which further comprises an upper electrode formed on the second stacked structure and surrounded by the circumferential wall, and

in which an area of a bottom surface of the upper electrode is equal to that of an upper surface of the second stacked structure.

5. The element according to claim 4 , wherein letting θ 2 be a taper angle of an upper portion of the circumferential wall, and θ 3 be a taper angle of a lower portion of the circumferential wall, a distance t 3 from an upper surface of the first nonmagnetic layer to an inflection point at which θ 2 <θ 3 satisfies t 3 >t 1 .

6. The element according to claim 5 , wherein letting θ 4 be a taper angle of the upper electrode, relationships indicated by

θ4>θ1,and θ3>θ1

are met.

7. The element according to claim 1 , wherein an amount of reaction product adhering to the circumferential surface of the second stacked structure is smaller than that of the first stacked structure.

8. The element according to claim 1 , wherein a resistance of the second nonmagnetic layer is lower than that of the first nonmagnetic layer.

9. The element according to claim 1 , wherein a hardness of the first nonmagnetic layer is higher than that of the second nonmagnetic layer.

10. The element according to claim 1 , wherein a change in magnetic characteristic of the first fixed layer caused by a reaction product is smaller than that of the second fixed layer.

11. The element according to claim 1 , wherein the circumferential surface of the second stacked structure has oxidized less than that of the first stacked structure.

12. The element according to claim 1 , wherein a magnetic anisotropic energy per unit volume of the second fixed layer is higher than that of the first fixed layer.

13. The element according to claim 1 , wherein a change in magnetic characteristic of the first fixed layer caused by damage is smaller than that of the second fixed layer.

14. The element according to claim 1 , wherein a reaction product adhering to the circumferential wall has oxidized.