Magnetization and anomalous Hall effect in SiO₂/Fe/SiO₂ trilayers

SiO₂/Fe/SiO₂ sandwich structure films fabricated by sputtering were studied by varying the Fe layer thickness (t _Fe). The structural and microstructural studies on the samples showed that the Fe layer has grown in nanocrystalline form with (1 1 0) texture and that the two SiO₂ layers are amorphous. Magnetic measurements performed with the applied field in in-plane and perpendicular direction to the film plane confirmed that the samples are soft ferromagnetic having strong in-plane magnetic anisotropy. The temperature dependence of magnetization shows complex behavior with the coexistence of both ferromagnetic and superparamagnetic properties. The transport properties of the samples as studied through Hall effect measurements show anomalous Hall effect (AHE). An enhancement of about 14 times in the saturation anomalous Hall resistance ($R_{\text{hs}}^{\text{A}}$) was observed upon reducing the t _Fe from 300 to 50 Å. The maximum value of $R_{\text{hs}}^{\text{A}}$  =  2.3 Ω observed for t _Fe  =  50 Å sample is about 4 orders of magnitude larger than that reported for bulk Fe. When compared with the single Fe film, a maximum increase of about 56% in the $R_{\text{hs}}^{\text{A}}$ was observed in sandwiched Fe (50 Å) film. Scaling law suggests that the R _s follows the longitudinal resistivity (ρ) as, $R_{\text{s}}\propto {\rho }^{1.9}$, suggesting side jump as the dominant mechanism of the AHE. A maximum enhancement of about 156% in the sensitivity S was observed. (paper)