Tunable Microwave Magnetism with Humidity Response Inspired by Pigment Cells

Controllable ferromagnetic resonance (FMR) peak shift is essential for spintronics, magnetic memory, and microwave sensing. However, realizing low-cost, nanoscale, and artificially tunable FMR remains challenging. Here, a nanoimprinting strategy is used to embed humidity-responsive hydrogel cores into magnetic nanocavities, inspired by biological pigment-cell modulation. Reversible swelling of the hydrogel generates localized stress and strain that couple magnetoelastically with the magnetic shell, enabling tunable resonance fields and microwave responses. Cycling tests confirm spontaneous, reversible, and durable modulation of magnetic properties under ambient humidity changes. A comparison between PMNs filled with 0% and 100% hydrogel core yields a resonance-field difference of ∼200 Oe, 3-6 times larger than previously reported values. And the swelling response of the hydrogel core further induces a 143-Oe shift with humidity change, without compromising structural integrity. These humidity-driven, magnetoelastically tunable nanomagnetic units provide a scalable pathway toward adaptive RF components and next-generation electromagnetic stealth materials.