Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning

Authors: Diane Gouéré, Hugo Merbouche, Aya El Kanj, Felix Kohl, Cécile Carrétéro, Isabella Boventer, Romain Lebrun, Paolo Bortolotti, Vincent Cros, Jamal Ben Youssef, and Abdelmadjid Anane

Thin garnet films are becoming central for magnon-spintronics and spin-orbitronics devices as they show versatile magnetic properties together with low magnetic losses. These fields would benefit from materials in which heat does not affect the magnetization dynamics, an effect known as the nonlinear thermal frequency shift. In this study, low-damping Bi substituted iron garnet (Bi:YIG) ultrathin films have been grown using pulsed laser deposition. Through a fine-tuning of the growth parameters, the precise control of the perpendicular magnetic anisotropy allows to achieve a full compensation of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are optimized, varying the growth temperature from ${405}^{\circ }C$ to ${475}^{\circ }C$ as the only tuning parameter induces the easy axis to go from out of plane to in plane. For films that are close to the dipolar compensation, ferromagnetic resonance measurements yield an effective magnetization ${\mu }_0{M}_{\mathrm{eff}}\left(T\right)$ that has almost no temperature dependence over a large temperature range (260 to 400 K) resulting in an anisotropy temperature exponent of 2. These findings put the Bi:YIG system among the very few materials in which the temperature dependence of the magnetic anisotropy varies at the same rate as the saturation magnetization. This interesting behavior is ascribed phenomenologically to the sizable orbital moment of ${\mathrm{Bi}}^{3+}$.