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High‐density magnetic memories are essential components for spintronics, quantum computing, and energy‐efficient electronics. Miniaturization of magnetic storage units requires reduced dimensionality and magnetic domain stability at the nanoscale. However, inducing magnetic order and selectively tuning spin‐orbital coupling at specific locations is challenging. Here, an unprecedented approach is demonstrated to construct switchable magnetic nanoislands in a nonmagnetic matrix based on cobaltite homostructures. The magnetic and electronic states are laterally modified by epitaxial strain, which is regionally controlled by freestanding membranes. Tensile‐strained cobaltite layers exhibit ferromagnetic properties, while compressively strained cobaltite layers exhibit a small magnetic response to applied fields. The minimum size of magnetic nanoislands reaches ≈35 nm in diameter, suggesting the highest possible areal density can reach upto ≈400 Gbit/in2. This methodology provides an ideal platform for precisely controlled read/write schemes and enables scalable and patterned memories on silicon and flexible supports for various applications. [ABSTRACT FROM AUTHOR]

Control of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast‐response information storage and processing devices. Previously, magnetic‐cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high‐quality single‐phase chromium oxynitride thin films using in‐situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (R3¯c) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads. [ABSTRACT FROM AUTHOR]