Magnetization Reversals of Fe81Ga19-Based Flexible Thin Films Under Multiaxial Mechanical Stress

The effect of multiaxial mechanical stress on angle-dependent magnetization reversals is studied on a single 10-nm ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ film, a single 10-nm ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ film, and a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$(10 nm)/${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$(10 nm) bilayer. These films are grown on flexible $\mathrm{Al}$ ``kitchenlike'' foils. These flexible foils are bent on two convex optical lenses to apply multiaxial mechanical stresses of different magnitudes. In order to understand the mechanisms driving the physical properties of the flexible systems, the magnetic films are also grown on hard native-oxide-covered $\mathrm{Si}$(100) substrates. By probing the angular dependence of the coercive field and the remanent magnetization, we show that the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ single layer and the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/{\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ bilayer grown on $\mathrm{Si}$ present a uniaxial anisotropy. Along their easy axis, their domain structure at the coercive field exhibits large domains with sawtooth domain walls. However, the ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ layer grown on $\mathrm{Si}$ shows a cubic anisotropy and sharp domain walls with a right-angle geometry along its easy axis. All layers grown on $\mathrm{Al}$ foils show development or enhancement of a uniaxial anisotropy arising from the $\mathrm{Al}$ surface morphology. Multiaxial mechanical stress applied to the flexible $\mathrm{Al}$ foils results in very different nonreversible effects as a function of the composition of the layered system. For ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$, multiaxial mechanical stress has no effect, as expected for a nonmagnetostrictive system. For ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$, it results in a full in-plane randomization of its magnetization-reversal properties. For the bilayer, multiaxial mechanical stress does not fully randomize the in-plane magnetization-reversal properties: the bilayer retains a uniaxial character.