MAGNETIC MEMORY DEVICE
According to one embodiment, a magnetic memory device includes a first magnetic layer having a variable magnetization direction, and including a first main surface and a second main surface located opposite to the first main surface, a second magnetic layer provided on a first main surface side of the first magnetic layer, and having a fixed magnetization direction, and a nonmagnetic layer provided between the first magnetic layer and the second magnetic layer, wherein a saturation magnetization of a part of the first magnetic layer which is located close to the first main surface is higher than a saturation magnetization of a part of the first magnetic layer which is located close to the second main surface.
1 . A magnetic memory device comprising:
a first magnetic layer having a variable magnetization direction, and including a first main surface and a second main surface located opposite to the first main surface;
a second magnetic layer provided on a first main surface side of the first magnetic layer, and having a fixed magnetization direction; and
a nonmagnetic layer provided between the first magnetic layer and the second magnetic layer,
wherein:
a saturation magnetization of a part of the first magnetic layer which is located close to the first main surface is higher than a saturation magnetization of a part of the first magnetic layer which is located close to the second main surface,
the first magnetic layer includes a first sub-magnetic layer, a second sub-magnetic layer, and a sub-nonmagnetic layer provided between the first sub-magnetic layer and the second sub-magnetic layer,
the first sub-magnetic layer includes a region close to the first main surface and has a first saturation magnetization,
the second sub-magnetic layer includes a region close to the second main surface and has a second saturation magnetization lower than the first saturation magnetization, and
the first sub-magnetic layer and the second sub-magnetic layer are in contact with the sub-nonmagnetic layer.
2 . The device of claim 1 , wherein the first magnetic layer contains iron (Fe) and boron (B).
3 . The device of claim 2 , wherein the first magnetic layer further contains cobalt (Co).
4 . The device of claim 3 , wherein a concentration of iron (Fe) in the part of the first magnetic layer which is located close to the first main surface is lower than a concentration of iron (Fe) in the part of the first magnetic layer which is located close to the second main surface.
5 . The device of claim 2 , wherein a concentration of boron (B) in the part of the first magnetic layer which is located close to the first main surface is lower than a concentration of boron (B) in the part of the first magnetic layer which is located close to the second main surface.
6 . The device of claim 2 , wherein the first magnetic layer further contains an added element selected from molybdenum (Mo) and tungsten (W), and
a concentration of the added element in the part of the first magnetic layer which is located close to the first main surface is lower than a concentration of the added element in the part of the first magnetic layer which is located close to the second main surface.
7 . The device of claim 1 , wherein the nonmagnetic layer contains magnesium (Mg) and oxygen (O).
8 . The device of claim 1 , wherein the sub-nonmagnetic layer has a thickness of 1 nm or more.
9 . The device of claim 1 , wherein the first sub-magnetic layer is thicker than the second sub-magnetic layer.
10 . The device of claim 1 , wherein the first magnetic layer has a saturation magnetization which increases from the second main surface toward the first main surface.
11 . The device of claim 1 , wherein an effective magnetic anisotropy energy of the part of the first magnetic layer which is located close to the first main surface is smaller than or equal to an effective magnetic anisotropy energy of the part of the first magnetic layer which is located close to the second main surface.