Magnetoresistive element, manufacturing method thereof and magnetic sensor

1. A magnetoresistive element comprising:

a magnetization free layer whose magnetization direction changes depending on an external magnetic field;

a magnetization pinned layer whose magnetization direction is pinned against the external magnetic field; and

a barrier layer that is positioned between the magnetization free layer and the magnetization pinned layer and that exhibits a magnetoresistive effect, wherein

the barrier layer is an oxide of an alloy that includes Mg and Al, and the barrier layer includes a crystalline region and a non-crystalline region, and

an atomic percent of Al in the alloy is 30% or more and 75% or less.

2. The magnetoresistive element according to claim 1 , wherein the alloy consists of Mg and Al.

3. The magnetoresistive element according to claim 1 , wherein the alloy further includes Zn or Ti or both Zn and Ti.

4. The magnetoresistive element according to claim 1 , wherein a volume ratio of the crystalline region in the barrier layer is 75% or more and 90% or less.

5. The magnetoresistive element according to claim 1 , wherein an atomic percent of Al in the alloy is 40% or more and 60% or less.

6. The magnetoresistive element according to claim 1 , wherein the magnetization free layer and the magnetization pinned layer include Co and Fe and further include at least any one of Si, B, N, and P.

7. A magnetoresistive element comprising:

a magnetization free layer whose magnetization direction changes depending on an external magnetic field;

a magnetization pinned layer whose magnetization direction is pinned against the external magnetic field; and

a barrier layer that is positioned between the magnetization free layer and the magnetization pinned layer and that exhibits a magnetoresistive effect, wherein

the barrier layer is an oxide of an alloy that includes Mg and Al, and the barrier layer includes a crystalline region and a non-crystalline region,

the magnetization pinned layer has a multilayer film in which a first magnetization pinned layer, a nonmagnetic intermediate layer, a second magnetization pinned layer and a CoFe layer that faces the barrier layer are sequentially stacked, and

at least either a portion of the second magnetization pinned layer that is adjacent to the CoFe layer or a portion of the magnetization free layer that is adjacent to the barrier layer is crystalline.

8. A magnetic sensor comprising the magnetoresistive element according to claim 1 .

9. A method of manufacturing a magnetoresistive element comprising the steps of:

forming either a magnetization free layer whose magnetization direction changes depending on an external magnetic field or a metal layer that is to be a magnetization pinned layer whose magnetization direction is pinned against the external magnetic field;

forming an alloy film that includes Mg and Al above either one of the layers, wherein an atomic percent of Al in the alloy film is 30% or more and 75% or less;

oxidizing the alloy film in order to form a barrier layer that has a magnetoresistive effect and that includes a crystalline region and a non-crystalline region;

forming a remaining one of the magnetization free layer and the metal layer above the barrier layer; and

pinning the magnetization direction of the metal layer in order to form the magnetization pinned layer.

10. A method of manufacturing a magnetoresistive element comprising the steps of:

forming either a magnetization free layer whose magnetization direction changes depending on an external magnetic field or a metal layer that is to be a magnetization pinned layer whose magnetization direction is pinned against the external magnetic field;

forming an alloy film that includes Mg and Al above said either one of the layers;

oxidizing the alloy film in order to form a barrier layer that has a magnetoresistive effect and that includes a crystalline region and a non-crystalline region;

forming a remaining one of the magnetization free layer and the metal layer above the barrier layer;

pinning the magnetization direction of the metal layer in order to form the magnetization pinned layer, wherein

a CoFe layer is provided between the barrier layer and the metal layer,

the magnetization free layer and the metal layer are amorphous, and

a portion of the magnetization free layer that is adjacent to the barrier layer and a portion of the metal layer that is adjacent to the CoFe layer are crystallized by annealing.