1. Field of the Invention
The present invention relates to a magneto-resistive element, a thin film magnetic head, a magnetic head device, and a magnetic recording/reproducing apparatus.
2. Description of the Related Art
Magneto-resistive elements are generally configured to have a magneto-resistive film above a lower magnetic shield film. Examples of the magneto-resistive film include a TMR (tunnel magneto-resistive) film and a CPP-GMR (current-perpendicular-to-plane giant magneto-resistive) film. MR change rates of the TMR and CPP-GMR films can improved by the following measures:
(1) For the TMR film, making a tunnel barrier layer out of crystalline magnesium oxide;
(2) For the CPP-GMR film, making a pinned or free layer out of an ordered Heusler alloy; and
(3) For the TMR or CPP-GMR film, making an antiferromagnetic layer out of an ordered IrMn alloy.
In the case of (1), however, high temperature annealing at a temperature equal to or greater than 300° C. is required in the production process to obtain sufficient MR change rate by crystallizing magnesium oxide. Also in the cases of (2) and (3), high temperature annealing at a temperature equal to or greater than 300° C. is required in the production process to obtain sufficient MR change rate by ordering the Heusler alloy or the IrMn alloy. During the high temperature annealing, the lower magnetic shield film will also be exposed to a high temperature equal to or greater than 300° C.
Generally, the lower magnetic shield film is a magnetic shield film made of a NiFe or CoFe alloy. In this case, however, when the magnetic shield film is exposed to a high temperature equal to or greater than 300° C., there is a possibility that the crystal grains will be grown and coarsened within the film. Coarsening of the crystal grains leads to deterioration of soft magnetic properties important for the magnetic shield film. For example, it increases coercive force and decreases magnetic permeability.
Japanese Unexamined Patent Application Publication No. H07-066034 discloses a soft magnetic film having a composition with P (phosphorus) added to NiFe. Moreover, Japanese Unexamined Patent Application Publication No. H04-196402 discloses a soft magnetic film having a composition with B (boron) added to CoFe. However, mere addition of P or B is insufficient to inhibit the coarsening of the crystal grains under a high temperature environment equal to or greater than 300° C.