Tunable Magnetism and Intrinsic Exchange Bias in Al-Substituted Terbium Iron Garnet

Ferrimagnetic insulators are central to both fundamental magnetism and diverse technologies, including spintronics, photonics, and microwave engineering. Their low damping, electrical insulation, and tunable magnetism make them ideal, especially for low-power spintronic devices. Controlling key magnetic properties -particularly the magnetic compensation- is essential for accessing ultrafast dynamics, and advanced spintronic functionalities. Here, it is demonstrated that the magnetic compensation temperature (T_M) of an archetype ferrimagnetic insulator, terbium iron garnet (Tb₃Fe₅O₁₂, TbIG), can be continuously tuned and raised to ambient temperature by partially substituting magnetic Fe atoms with nonmagnetic Al. This substitution, achieved by high-temperature co-sputtering of TbIG and Al₂O₃, is confirmed by atomically resolved electron microscopy. Near T_M, a giant intrinsic exchange bias of up to 2.5 kOe is observed. The exchange bias exhibits deterministic or stochastic behavior depending on the cooling conditions, and its polarity can be controlled via an external magnetic field. To explain the observed phenomena, a phenomenological model is developed that takes into account a distribution of local T_M values induced by magnetic site disorder. These findings provide an efficient strategy for controlling T_M and enabling exchange bias in TbIG that may add new functionalities for room-temperature spintronic and photonic applications.