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The control of pure spin currents carried by magnons in magnetic insulator (MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of great interest to spintronic technology as they can be used to carry, transport, and process information. Garnet films with PMA have labyrinth domain magnetic structures that enrich the magnetization dynamics and could be employed in more efficient wave-based logic and memory computing devices. In MI/non-magnetic (NM) bilayers, where NM is a normal metal providing a strong spin–orbit coupling, the PMA benefits the spin–orbit torque-driven magnetization switching by lowering the needed current and rendering the process faster, crucial for developing magnetic random-access memories. In this work, we investigated the magnetic anisotropies in thulium iron garnet (TIG) films with PMA via ferromagnetic resonance measurements, followed by the excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven by microwaves and heat currents. TIG films presented a Gilbert damping constant of α ≈0.01, with resonance fields above 3.5 kOe and half linewidths broader than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through TIG/Pt was observed as a microvoltage generated at the edges of the Pt film. The obtained spin Seebeck coefficient was 0.54 μV/K, also confirming the high interfacial spin transparency.

The active manipulation of quasiparticles, other than electrons, is a feasible alternative for developing the next generation of devices for information processing. Exploring magnons is advantageous as they can travel far and fast due to their low dissipation and high group velocity, transferring spin without charge transport, thus reducing the Joule heating. Moreover, magnon currents can switch a film's magnetization via a magnon torque facilitated by a perpendicular magnetic anisotropy (PMA). We demonstrate the proof of principle for three states' memories via transport studies of thermally excited magnon currents at room temperature in ferrimagnetic insulating magnon valves TmIG/Au/TmIG with PMA. While varying the relative TmIG magnetizations orientation, magnon currents excited in TmIG films are detected as a voltage in a top platinum electrode film due to the inverse spin Hall effect. The magnon transmission is maximum in the parallel state where the two signals sum up. Possibilities are seen for wave-based nonvolatile magneto-resistive random-access memory, sensing, and logic devices.

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The longitudinal spin Seebeck effect (LSSE) has been investigated in ZnFe2O4 (ZFO) thin films on different substrates, such as Si (111), MgO (100), and SrTiO3 (100). The LSSE voltage signal exhibited a linear dependence on the temperature difference between both sides of the samples. The spin Seebeck coefficients were highly sensitive to the thermal conductivities of the magnetic layer and substrate, with values from 3 nV/k to 110 nV/K. Charge currents ($${J}_{\mathrm{c}}$$ J c ) and spin currents ($${J}_{\mathrm{s}}$$ J s ) densities were estimated. $${J}_{\mathrm{s}}$$ J s values are similar for the samples deposited on MgO and STO. The saturation magnetic field for the LSSE signal was reached with a magnetic field lower than its bulk counterpart. These results were related to the lattice mismatch between the ZFO films and the substrate, the magnetic response, and the anisotropies present in the samples since a twofold in-plane anisotropy was observed for the sample deposited on Si, while the samples deposited on MgO and SrTiO3 showed a fourfold in-plane anisotropy. Moreover, the presence of a notable perpendicular magnetic anisotropy in the thin films may be a consequence of the lattice mismatch and at the same time, it can cause the saturation in the LSSE voltage hysteresis loop measured as a function of the external magnetic be reached with a low magnetic field.