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Aiming to realize the integration of signal processing with the human body, wearable and implantable radio frequency (RF)/microwave devices are rapidly developed. However, the insufficiency in skin commonality and biocompatibility brings up challenges in making such devices. In this study, an ultra-flexible and biocompatible CoFeB/silk film is developed potentially for on-skin and implantable RF/microwave applications. Moreover, the CoFeB/silk films present controllable dissolvability in aqueous solutions and exhibit great potentials in applications for environmentally friendly disposable devices. A strain-tunable bandstop filter based on the CoFeB/silk film was fabricated, which exhibited a large frequency tunability of 3 GHz and ability in monitoring the finger-joints’ motions. This concept and method of combining ferromagnetic materials with the biocompatible substrate offers a novel pathway for wearable/implantable applications.

The tunable range of RF/microwave devices is limited not only due to the difficulty in growing high-quality magnetic oxide thin films but also because of their low magnetostrictive coefficient as in Y3Fe5O12(YIG) thin films. In this work, we have fabricated flexible YIG thin films by using pulsed laser deposition (PLD) technology, which exhibit a low-damping constant (2.67 × 10−4) and well-established magnetic properties suitable for RF/microwave materials. A noticeable ferromagnetic resonance (FMR) field shift of 180 Oe was obtained along the out-of-plane direction viaa flexible tunable factor f(R), which results in a frequency shift as high as 550 MHz. The result shows a greater FMR tuning than that induced by ferroelectric single crystals. At the same time, a systematic theoretical framework for tuning FMR characteristics was presented for the flexible YIG/mica thin films, which would provide an effective tuning method for other flexible magnetic oxides with low magnetostrictive coefficients. Last but not least, a flexible coplanar waveguide (CPW) integrated with the flexible YIG thin films shows excellent microwave magnetic stability and fatigue-resistant behavior. It would open a new door for further applications, such as flexible spiral detectors and high-frequency signal processors in the near future.

La0.7Sr0.3MnO3(LSMO) is one of the most fascinating strongly correlated oxides in which the spin polarization and magnetic property are sensitive to strain, especially in the (111)-oriented LSMO. In the paper, epitaxial LSMO(111) thin films with different thicknesses were prepared, and they showed continuous dislocation defect arrays with thickness greater than 45 nm. Then, the thick LSMO(111) films were divided into a double-layer structure with two slightly different oriented cells. The LSMO(111) films present a stronger lattice–spin coupling, thus the double-layer structure triggers an obvious magnetic heterogeneity phenomenon (magnetic bi-states) by the way of creating a double-mode ferromagnetic resonance (FMR) spectrum. Therefore, the nanostructures, especially the ordered structure defects, may trigger enriched physical phenomena and offer new forms of spin coupling and device functionality in strain-sensitive strongly correlated oxide systems.