Recently, a spontaneous exchange bias (SEB) driven by the isothermal crystallization of the antiferromagnetic IrMn layer has been reported in IrMn/FeCo bilayer. However, the key factors to determine the magnitude of SEB have not been clearly understood yet. Here, we investigate the effect of isothermal crystallization in IrMn layer on the formation of SEB in IrMn/CoFeB bilayer through preparing the samples with different degrees of isothermal crystallization in IrMn layer. The SEB is negligible in the sample with more structure-stable IrMn layer, confirming that the isothermal crystallization of IrMn plays a crucial role in the formation of SEB. However, the SEB field does not change significantly with the free-relaxation time of IrMn/CoFeB bilayers or IrMn layer. These results indicate that a slight degree of isothermal crystallization in IrMn layer is sufficient to induce a large SEB in IrMn/CoFeB bilayer. Our results not only confirm the newly reported SEB driven by the isothermal crystallization in IrMn layer but also clarify the key factor to control the magnitude of SEB.

The wrinkling structures, which can greatly improve the stretchability of the metallic thin films, have been widely used in the preparation of stretchable devices. However, the artificial wrinkling structures are often accompanied by the generation of microcracks, which seriously affect the performance of the devices. In this work, by establishing the corresponding model, the transverse strain of the longitudinally prestrained continuous film and the strip film is mechanically analyzed, which is verified by experimental results; for the strain of blank substrate, the error of the model was about 3.7%. It is difficult to avoid the generation of microcracks with continuous films, but strip films can avoid the generation of microcracks to a certain extent. The experimental results illustrate the various factors affecting the generation of microcracks. The transverse strain of the film is proportional to the substrate’s Young’s modulus, Poisson’s ratio, thickness, and prestrain and is basically inversely proportional to the strip film’s Young’s modulus, thickness, and strip interval. Our results provide deeper knowledge for choosing proper metallic materials to fabricate stretchable wrinkled devices.