Exchange coupling film and magnetoresistive element using the same
View Patent ↗A PtMn alloy film known as an antiferromagnetic material having excellent corrosion resistance is used for an antiferromagnetic layer. However, an exchange coupling magnetic field is decreased depending upon the conditions of crystal grain boundaries. Therefore, in the present invention, the crystal grain boundaries formed in an antiferromagnetic layer (PtMn alloy film) and the crystal grain boundaries formed in a ferromagnetic layer are made discontinuous in at least a portion of the interface between both layers. As a result, the antiferromagnetic layer can be appropriately transformed to an ordered lattice by heat treatment to obtain a larger exchange coupling magnetic field than a conventional element.
1. An exchange coupling film comprising an antiferromagnetic layer and a ferromagnetic layer, which are formed in contact with each other so that a magnetization direction of the ferromagnetic layer is pinned in a predetermined direction by an exchange coupling magnetic field produced at an interface between both layers, wherein the antiferromagnetic layer is made of an antiferromagnetic material comprising an element X (at least one element selected from Pt, Pd, Ir, Rh, Ru, and Os) and Mn;
in a section of the exchange coupling film in parallel with a thickness direction thereof, crystal grain boundaries formed in the antiferromagnetic layer and a crystal grain boundaries formed in the ferromagnetic layer are discontinuous in at least a portion of the interface; and
wherein the antiferromagnetic layer and the ferromagnetic layer are laminated in this order from the bottom, and a seed layer is disposed below the ferromagnetic layer and has a crystal structure mainly composed of a face-centered cubic crystal in which equivalent crystal planes represented by the {111} plane are preferentially oriented in parallel with the interface.
2. An exchange coupling film according to claim 1 , wherein in the antiferromagnetic layer and the ferromagnetic layer, equivalent crystal planes represented by a {111} plane are preferentially oriented in parallel with the interface.
3. An exchange coupling film according to claim 1 , wherein the seed layer is made of a NiFe alloy, Ni, a Ni—Fe—Y alloy (wherein Y is at least one element selected from Cr, Rh, Ta, Hf, Nb, Zr, and Ti), or a Ni—Y alloy.
4. An exchange coupling film according to claim 3 , wherein the seed layer is represented by the composition formula (Ni 1−x Fe x ) 1−y Y y (x and y are atomic ratios) wherein the atomic ratio x is 0 to 0.3, and the atomic ratio y is 0 to 0.5.
5. An exchange coupling film according to claim 1 , wherein the seed layer is nonmagnetic at normal temperature.
6. An exchange coupling film according to claim 1 , further comprising an underlying layer formed below the seed layer and comprising at least one element selected from Ta, Hf, Nb, Zr, Ti, Mo and W.
7. An exchange coupling film according to claim 1 , wherein at least a portion of the interface between the antiferromagnetic layer and the seed layer is in an incoherent state.
8. An exchange coupling film according to claim 1 , wherein the seed layer is disposed below the antiferromagnetic layer.