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Amorphous magnetic alloys with large perpendicular magnetic anisotropy (PMA) have emerged as a suitable material choice for spintronic memory and high-frequency non-reciprocal devices on-chip. Unlike ferromagnets, ferrimagnets offer faster switching dynamics, lower net saturation magnetization, minimal stray field and a lower net angular momentum. Ferrimagnetic thin films of Gd x Co 1− x sputter deposited as heterostructures of Ta/Pt/Gd x Co 1− x (t)/Pt on Si/SiO 2 have bulk-like PMA for thicknesses of 5–12 nm and room-temperature magnetic compensation for x = 28–32%. Preferential oxygenation of GdCo has been found to increase the effective anisotropy energy density by an order of magnitude and produce near-ideal remanence ratios. X-ray photoelectron spectroscopy accurately quantifies the metal-oxidation ratio, which shows that an oxygen-rich and Co-deficient stoichiometry (Gd 21 Co 28 O 51 ) likely weakens the ferromagnetic exchange interaction between Co–Co and contributes additional antiferromagnetic exchange through superexchange-like interactions between Gd and Co via O, resulting in a stronger out-of-plane magnetization. Even greater PMA and giant-anisotropy field of 11 kOe are achieved in super-lattices of the Gd 21 Co 28 O 51 heterostructure. The combination of ferrimagnetic ordering in amorphous Gd x Co 1− x and its affordance of pathways for engineering large PMA will enable the design of integrated high-frequency devices beyond 30 GHz and ultrafast energy efficient memory devices with switching speeds down to tens of picoseconds. 

Abstract The precise control of magnetic properties at the microscale has transformative potential in healthcare and human‐robot interaction. This research focuses on understanding the magnetic interactions in nanostructure assemblies responsible for microactuation. By combining experimental measurements and micromagnetic simulations, the interactions in both nanocube and nanochain assemblies are elucidated. Hysteresis measurements and first‐order reversal curves (FORC) reveal that the spatial arrangement of these assemblies governs their collective magnetism. A critical concentration threshold is observed where a transition from ferromagnetic‐like to antiferromagnetic‐like coupling occurs. Leveraging the high uniaxial anisotropy of 1D nanochains, the remanent magnetization of assembled chain structures is maximized for efficient magneto‐mechanical energy transduction. By utilizing an optimized magnetic nanostructure concentration, a flexible film is fabricated, and its significantly enhanced mechanical deformation response to a small magnetic field, surpassing conventional particle‐based samples by a factor of five, is demonstrated. Demonstrating excellent transduction efficiency, visible deformations such as bending and S‐shaped twisting modes are achieved with an applied field of less than 400 Oe. Furthermore, the reprogrammability of the actuator, achieving a U‐shaped bending mode by altering its magnetization profile, is showcased. This research provides valuable insights for designing reconfigurable and effective microactuators and devices at significantly smaller scales than previously possible.