TITLE: FMR and Thermal Spin Pumping in Garnets|Pt Bilayers.
AUTHORS (LAST NAME, FIRST NAME): Solís, Lara M.; Carreira, Santiago; Aguirre, Myriam; Steren, Laura; Butera, Alejandro; Gómez, Javier; Briático, Javier; García, Carlos.
INSTITUTIONS (ALL): 1. Centro Atomico Constituyentes, San Martin, Buenos Aires, Argentina. 2. Universidad de Zaragoza Instituto de Nanociencia de Aragon, Zaragoza, Aragon, Spain. 3. Universidad de Zaragoza Departamento de Fisica de la Materia Condensada, Zaragoza, Aragón, Spain. 4. Unite Mixte de Physique CNRS/Thales, Palaiseau, Île-de-France, France. 5. Centro Atomico Bariloche, Bariloche, Río Negro, Argentina. 6. Universidad Tecnica Federico Santa Maria Departamento de Fisica, Valparaiso, Valparaíso, Chile.
ABSTRACT BODY: Digest Body: The YFeO (YIG) ferrimagnetic insulator is recognized as a model system for spintronic andmagnonic phenomena, including spin pumping, spin Seebeck, proximity effects, and spin wave propagation. Inthese materials, the spin current is produced by spin-waves or magnons. Magnons can be electrically excitedand sensed via the Spin Hall Effect (SHE) and Anomalous Spin Hall Effect (ASHE) or they can be thermallyexcited through the Spin Seebeck Effect (SSE). To detect the spin current, a thin non-magnetic layer such asPt is deposited on top of the material of interest. This transforms the spin current into an observablethermoelectric voltage (V) via the Inverse Spin Hall Effect (ISHE). Pt/YIG systems allow efficient spin-charge conversion and pure detection of spin-current effects, respectively, due to their unique magneto-opticaland spin dynamic properties . These properties allow a clean detection of the pure spin current thanks to thespin-orbit effects in the Pt/YIG microstructures . Additionally, Rare Earth (RE) garnet films are magnetic andmagnetoelastic, and their properties can be manipulated through choice of composition and substrate. When aproportion of bismuth (Bi) is added, the magneto-optical properties of YIG increase according to theconcentration of bismuth (Bi) at the yttrium site . But there are few studies on how the spin dynamicproperties are modified due to this substitution. In this work we study different parameters in the manufactureof ferrimagnetic/non-magnetic bilayers to raise the thermoelectric spin voltage V. Samples with different thicknesses of pure YFeO (YIG) films and a 5% Bi substitution, that is, thin films ofBiYFeO (BiYIG), were grown on GdGaO(111) and GdScGaO(111) substrates by pulsed laserdeposition (PLD). XRD, HR-TEM / STEM-HAADF and GPA measurements revealed high quality crystallinefilms as it can be seen in Figure 1. Ferromagnetic resonance (FMR) measurements were performed at roomtemperature for all heterostructures. A resonance field (Hres) and a resonance linewidth (FWHM) wereextracted and are shown in Figure 2 as a function of frequency. These values allow the calculation of a Gilbertdamping coefficient that is directly correlated with the SSE according to Chang et. Al . In our case, theGilbert damping coefficient is (5-14)x10 for the YIG//GGG samples and (18-19) x10 for the YIG//SGGGsamples. The linewidth of BiYIG samples is much wider. After growth of an 8 nm-Pt coating layer by sputtering,the damping in all the samples increases due to the contribution due to spin pumping from the YIG or BiYIG tothe metal film. The difference between the H result and the bulk value of 4πMreported (1750 G )demonstrates the existence of a perpendicular anisotropy. With a maximum 20K thermal difference across the entire structure, we measure longitudinal SSE voltages inboth YIG and BiYIG samples with sputtered Pt. The YIG//SGGG combination reported to have the best voltagesignal from the Inverse spin-Hall effect (V) and Spin Seebeck Effect (V), along with the co-occurrenceof a positive perpendicular anisotropy. In the case of the BiYIG samples, the voltages induced in theBiYIG//SGGG bilayers were lower with respect to YIG//SGGG but higher with respect to YIG//GGG. Thesamples with the lowest perpendicular magnetic anisotropy showed the highest V in both cases, YIG andBiYIG. This work is funded thanks to the SPICOLOST (GA 734187) project framed within “Horizon 2020 Funding” ofthe European Union with the MARIE SKLODOWSKA-CURIE – RISE Actions (Research and Innovation StaffExchanges) program coordinated by the University of Zaragoza. References:  S. M. Rezende, R. L. Rodríguez-Suárez, and R. O. Cunha, Physical Review B, Vol. 89, p.