The authors report on a systematic investigation of the longitudinal spin Seebeck effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an in‐plane magnetic easy axis with a compensation temperature (TComp) that decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31 nm, respectively. For all the films, the LSSE signal flips its sign below TComp. The authors demonstrate a universal scaling behavior of the temperature dependence of LSSE signal for the GdIG films around their respective TComp. Additionally, the authors demonstrate LSSE in a 31 nm GdIG film grown on a lattice‐mismatched GSGG (Gd3Sc2Ga3O12) substrate that exhibits an out‐of‐plane magnetic easy axis at room temperature. However, this sample reveals a spin reorientation transition where the magnetic easy axis changes its orientation to in‐plane at low temperatures. A clear distinction is observed in the LSSE signal for the GSGG/GdIG(31 nm)/Pt heterostructure, relative to GGG/GdIG(31 nm)/Pt showing an in‐plane magnetic easy axis. The findings underscore a strong correlation between the LSSE signal and the orientation of magnetic easy axis in compensated ferrimagnets and opens the possibility to tune LSSE through effective anisotropy.

Electrical and magnetic transport properties of FeSi-SiO 2-Si junctions fabricated by depositing FeSi thin films on silicon substrates with the native oxide layer have been investigated. Near room temperature the carriers tunneled across the interface to the substrate with low resistance. With a decreasing temperature, the junction resistance increased more than three orders of magnitude near 270 K, which switched the current path to the film. The transition characteristics depend on the conductivity of the silicon substrate. A positive magnetoresistance that peaked near the transition temperature was observed. Similar behavior was seen for CoSi films while TiSi films did not show a transition in resistance.

Ionic engineering is exploited to substitute Bi cations in BiFe0.95Mn0.05O3 NPs (BFM) with rare-earth (RE) elements (Nd, Gd, and Dy). The sol-gel synthesized RE-NPs are tested for their magnetic hyperthermia potential. RE-dopants alter the morphology of BFM NPs from elliptical to rectangular to irregular hexagonal for Nd, Gd, and Dy doping, respectively. The RE-BFM NPs are ferroelectric and show larger piezoresponse than the pristine BFO NPs. There is an increase of the maximum magnetization at 300 K of BFM up to 550% by introducing Gd. In hyperthermia tests, 3 mg/ml dispersion of NPs in water and agar could increase the temperature of the dispersion up to ∼39°C under an applied AC magnetic field of 80 mT. Although Gd doping generates the highest increment in magnetization of BFM NPs, the Dy-BFM NPs show the best hyperthermia results. These findings show that RE-doped BFO NPs are promising for hyperthermia and other biomedical applications.

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He has authored or co-authored over 165 peer-reviewed technical articles. His current research interests include magnetic materials for energy applications, including soft-magnetic and magnetocaloric materials. Prof. Franco served as the Chair for the Spain Chapter of the IEEE Magnetics Society and Magnetic Materials Committee of the Minerals, Metals and Materials Society. He was a recipient of the Young Scientist Award from the Royal Physical Society of Spain in 2000. He has been an Editor and the Publications Chair of several Magnetism and Magnetic Materials (MMM) Conferences and will be the General Chair of the 2022 Joint MMM-Intermag Conference.