We have investigated the magnetic properties of amorphous Co40Fe40B20 (CoFeB) thin films grown on flexible polyimide (PI) substrates, which were fixed on convex molds with different curvatures during the magnetron sputtering deposition. When the flexible substrates were changed from convex to flat state after fabrication, a uniaxial magnetic anisotropy was induced in the CoFeB film due to magnetostrictive effect. Furthermore, the anisotropy also depends on the thicknesses of the film and substrate. Our results demonstrate a convenient method to tune the anisotropy of magnetic thin films grown on flexible substrates.
Spin valve devices, consisting of a free magnetic layer, a spacer layer, and a pinned magnetic layer, are widely used in magnetic sensors and nonvolatile magnetic memories. However, even a slight bending deformation can affect the magnetization direction of the free magnetic layer, which will change the magnetoresistance signal of the devices. Therefore, it is a challenge to develop a flexible spin valve device with controllable performance. Here, an enhanced stress-invariance of the magnetization direction in amorphous CoFeB magnetic films on flexible polyimide substrates is achieved. The uniaxial anisotropy is induced by growing on the bent substrate under a magnetic field, which aligns more magnetic domains with easy axes along the direction perpendicular to the subsequently applied stress. Theoretical calculations indicate that pre-induced anisotropy with an easy axis perpendicular to the applied stress effectively resists the change in the magnetization direction during bending. These results are of importance for realizing better performance of flexible spin valve devices and the development of flexible spintronics. Published by AIP Publishing.
A new FePt nanostructure with stripe-like patterns has been prepared by direct current (DC) magnetron sputtering on anodic aluminum oxide (AAO) templates. AAO templates anodized under low voltages (7 V) demonstrate self-organized, maze-like patterns, different from the conventional porous structures obtained at high voltages. FePt thin films deposited on such templates tend to replicate the morphology of the templates. Although there is no obvious spatial ordering, the dimensions of the FePt nano-stripes are highly uniform, due to the constrained growth along the transverse direction of the AAO pattern. The magnetic properties are strongly influenced by this unique morphology. While continuous films demonstrate strong exchange coupling, the dominant interaction in FePt nano-stripes with the same nominal thickness is magnetostatic. The morphology also dictates the magnetization reversal behaviors, with thin films dominated by domain nucleation; while nano-stripes incline to reverse their magnetization by spin rotation. Our work demonstrates that self-organized AAO templates can be used to control the morphology and magnetic behavior of FePt materials.
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