Giant Non-Monotonic Temperature-Controlled Magnetic Anisotropy in FeGa-B/LiNbO ₃ Magnetoelastic Heterostructures

Thermally reconfigurable magnetic anisotropy offers a compelling route to adaptive spintronic and microwave functionalities. Here, we report a giant, non-monotonic, temperature-controlled magnetic anisotropy (TCMA) in FeGa-B thin films deposited on YZ- cut LiNbO 3 (LNO) substrates, reaching up to ∼ 12% K −1 and producing an order-of-magnitude modulation (~6×) of the effective anisotropy within a modest ~75 K temperature window, corresponding to an overall change of nearly 820%. Angle-resolved magneto-optical Kerr effect (MOKE) and vector-network-analyzer ferromagnetic resonance (VNA-FMR) measurements reveal a well-defined in-plane uniaxial magnetic anisotropy (UMA) with a two-fold symmetry that rotates by 90° in high-boron films. Temperature-dependent magnetometry uncovers a reversible interchange of the easy and hard axes, accompanied by a pronounced non-monotonic evolution and sign reversal of the effective anisotropy. This behavior is attributed to the anisotropic thermoelastic stress arising from the crystallographically dependent thermal expansion of LNO (α x ≠ α z ), which couples to the film's magnetostriction and drives a temperature-dependent sign reversal of the magnetoelastic anisotropy. The demonstrated strain-driven, thermally adaptive anisotropy offers a robust and scalable pathway toward self-compensating and temperature-tunable magnetic architectures for high-frequency spintronic, sensor, and microwave applications.