Interlayer coupling field in spin valves with CoFe/Ru/CoFe/FeMn synthetic antiferromagnets (invited)

Top synthetic spin valves with structure $\mathrm{Ta/NiFe/CoFe/Cu/CoFe}\text{(P1)/}\mathrm{Ru/CoFe}\text{(P2)/}\mathrm{FeMn/Ta}$ on Si (100) substrate with natural oxide were prepared by dc magnetron sputtering system. We have changed only the thickness of the free layer and the thickness difference $\text{(P1−P2)}$ in the two ferromagnetic layers separated by Ru, and investigated the effect of magnetic film thickness on the interlayer coupling field in a spin valve with a synthetic antiferromagnet. As the free layer thickness decreased from 70 to 20 Å, the interlayer coupling field was increased due to the magnetostatic coupling (orange peel coupling). In the case of the thickness difference in the pinned layers, the interlayer coupling field agreed with the modified Néel model suggested in the top synthetic spin valve structures. However, in the case of $t_{\text{P1}}{\mathrm{=t}}_{\text{P2}},$ and $t_{\text{P1}}{\mathrm{=t}}_{\text{P2}}\text{+5\hspace{0.05em}Å,}$ it was found that the interlayer coupling field could not be explained by the modified Néel model. The deviation of the modified Néel model at the dip zone could be due to the large canting of the pinned layers, which depend on applied field and different thickness in synthetic antiferromagnetic structure. The dependence of Cu thickness on the interlayer coupling field was investigated and 10 Oe of the interlayer coupling field was obtained when the Cu thickness is 32 Å.