Magnon propagation and spin diffusion length in low-loss lithium aluminum ferrite thin films

Spintronics integrated with low-loss ferromagnetic insulating thin films enables pure spin current-based spintronics, reducing losses from dissipative charge currents and improving energy efficiency over conventional microelectronics. We have identified the ferromagnetic insulator Li_0.5Al_1.0Fe_1.5O₄ (LAFO) as a promising candidate for spintronics due to its low Gilbert damping parameter (~10^-4). To understand magnon transport, we have studied the spin diffusion length, 𝜆_m, of magnons in LAFO grown on MgAl₂O₄ (MAO) substrates as a function of temperature. We employ a non-local measurement geometry using two Pt electrodes on top of LAFO separated by 0.2 µm to 10 µm. In our experiment, magnons are excited in one electrode both electrically (via the spin Hall effect) and thermally (via the spin Seebeck effect) and are electrically detected in the other electrode via the inverse spin Hall effect. We can distinguish contributions of the electrically and thermally generated magnons via harmonic measurements. At 280 K, both electrically and thermally generated magnons yield 𝜆_m ~ 2.5 µm. However, as a function of decreasing temperature, electrically generated magnons show slightly decreasing 𝜆_m, approaching ~1.8 µm at 100 K, while thermally generated magnons show 𝜆_m increasing to ~4 µm at 10 K. These results suggest that the two generation methods are not equivalent and create an opportunity for manipulating the spin diffusion length using temperature and magnon generation type in spintronic applications.