MAGNETORESISTIVE ELEMENT

1 . A magnetoresistive element comprising:

a storage layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is variable;

a reference layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is invariable;

a tunnel barrier layer as a nonmagnetic layer formed between the storage layer and the reference layer; and

a first underlayer formed on a side of the storage layer, which is opposite to a side facing the tunnel barrier layer, and containing amorphous W.

2 . The element of claim 1 , further comprising a second underlayer formed on a side of the first underlayer, which is opposite to a side facing the storage layer, and containing an amorphous conductive material.

3 . The element of claim 2 , wherein the conductive material is a metal to which a metalloid is added.

4 . The element of claim 2 , wherein the conductive material is CoFeB.

5 . The element of claim 2 , wherein the second underlayer contains W.

6 . The element of claim 2 , wherein the second underlayer is a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is variable.

7 . The element of claim 2 , wherein a thickness of the first underlayer is 8 Å or more to 20 Å or less, and a thickness of the second underlayer is 1 Å or more to 20 Å or less.

8 . The element of claim 2 , wherein a thickness of the first underlayer is 1 Å or more to 3 Å or less, and a thickness of the second underlayer is 3 Å or more to 15 Å or less.

9 . The element of claim 1 , wherein a thickness of the first underlayer is not more than 20 Å.

10 . The element of claim 2 , wherein the second underlayer further contains a crystalline conductive material.

11 . The element of claim 1 , wherein the storage layer contains crystalline CoFeB.

12 . The element of claim 1 , wherein a thickness of the storage layer is 8 Å or more to 15 Å or less.

13 . The element of claim 2 , further comprising a buffer layer formed on a side of the second underlayer, which is opposite to a side facing the first underlayer, and containing one of W, Mo, and Ta.

14 . A magnetoresistive element manufacturing method comprising:

forming a first underlayer containing amorphous W;

forming, on the first underlayer, a storage layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is variable;

forming a tunnel barrier layer as a nonmagnetic layer on the storage layer; and

forming, on the tunnel barrier layer, a reference layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is invariable.

15 . The method of claim 14 , further comprising forming a second underlayer containing an amorphous conductive material, before the forming the first underlayer,

wherein the first underlayer is formed on the second underlayer.

16 . The method of claim 14 , wherein the first underlayer is formed by sputtering, and has a thickness of not more than 20 Å.

17 . The method of claim 14 , wherein the second underlayer, the first underlayer, the storage layer, and the reference layer are formed by sputtering in a first chamber, and the tunnel barrier layer is formed by sputtering in a second chamber different from the first chamber.

18 . The method of claim 14 , further comprising performing annealing after the forming the reference layer, wherein the first underlayer contains amorphous W after the annealing.

19 . The method of claim 18 , wherein the second underlayer partially crystallizes in the annealing.

20 . A magnetoresistive element manufacturing method comprising:

forming a reference layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes, and in which a magnetization direction is invariable;

forming a tunnel barrier layer as a nonmagnetic layer on the reference layer;

forming, on the tunnel barrier layer, a storage layer as a ferromagnetic layer which has magnetic anisotropy perpendicular to film planes and contains amorphous CoFeB, and in which a magnetization direction is variable; and

forming a first underlayer containing amorphous W on the storage layer.