Effects of uniaxial stress on the magnetic properties of thin films and GMR sensors prepared on polyimide substrates

Abstract

The effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo‐spin‐valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (∼1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in‐plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto‐optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in‐plane four‐point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (Hext), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stretchable Magnetoelectronics

“…Although the supports used in these studies are considered rigid, they allow for a small amount of bending deformation, which is translated to the functional magnetic layers on the outer surface as a tensile deformation (bending strain) of the order of about 0.1%. Later, similar studies were performed using plastic polyimide substrates 106 , which allowed for magnetoelectric measurements at tensile strains of up to 0.75% directly applied by stretching 107 . Higher levels of deformation were obtained by Y.F.…”

Dynamic electro-chemo-mechanical analysis during cyclic voltammetry

“…21 Note also that the strain amplitude never exceeded 10 À3 , whereas in situ X-ray diffraction shows that similar films deform coherently with the substrate up to the much larger strain amplitude of 1%. 29…”

Shapeable magnetoelectronics

“…Later, similar studies were performed using plastic polyimide substrates, 106 which allowed for magnetoelectric measurements at tensile strains of up to 0.75% directly applied by stretching. 107 Higher levels of deformation were obtained by Chen et al, who deposited extended GMR films on buffer coated polyester transparency, as shown in Figure 5(a). 68 No performance degradation was observed in the magnetoresistive elements after 1000 bending cycles to a radius of about 22 mm.…”