Giant magnetoresistive(GMR) spin valve layered structure is becoming one of the most promising read out candidates for ultrahigh density magnetic recording. The basic structure of the spin valve system consists of ferromagnetic layer/space layer/ferromagnetic layer/ anti-ferromagnetic layer. The ferromagnetic $Ni_{80}Fe_{20}$ film shows highly sensitive switching response because of low coercivity force, whereas the Co film displays high MR value due to its high spin-dependant scattering property. The spin valve system with Ta underlayer have strong (111) texture and the NiFe layer neighboring the FeMn antiferromagnetic layer is strongly exchange-biased by the (111) FeMn layer.
In this paper, the film structure investigated was the top spin valve system consisting typically of Si/Hf 100Å/NiFeCo 40Å/Cu 20Å/NiFeCo 40Å/FeMn 80Å/Hf 25Å. The variation of Co content in the NiFeCo ferromagnetic film showed that the MR increases by 90% from 3.0% to 5.7% without much increment of the coercive force( <20 Oe) as the Co content increased from 0% to 23at.% in the $Ni_{80}Fe_{20}$ film. But as the Co content increased further to 27 at.%, the MR decreased with a concurrent weakening of (111) texture. We found that the increase of MR with Co content is closely associated with the dissolution of significant amount of Co into NiFe lattice and a concurrent (111)texture change. When the Ta underlayer was replaced by Hf, the MR increased by 14%, i.e., from 4.4% to 5.0% and $H_{ex}$ also increased by 23%, i.e., from 204 Oe to 251 Oe. The improvement in MR and $H_{ex}$ is believed to result mainly from the development of smooth interface between the ferromagnetic and spacer layers and between the antiferromagnetic and ferromagnetic layer respectively. The development of smooth interface is because the surface energy is significantly low in the case of Hf film as compared to the Ta film. The variation of deposition power of ferromagnetic layer showed that the MR increases by 37%, i.e., from 4.1% to 5.6% together with a simultaneous decrease in $H_{ex}$ by 13% from 265 Oe to 238 Oe as the power increases from 24W to 77W. This was interpreted as largely due to significant decrease of sheet resistance which is caused by grain growth with the deposition power.
