Spin Seebeck Effect in Iron Oxide Thin Films: Effects of Phase Transition, Phase Coexistence, And Surface Magnetism

Abstract

Understanding impacts of phase transition, phase coexistence, and surface magnetism on the longitudinal spin Seebeck effect (LSSE) in a magnetic system is essential to manipulate the spin to charge current conversion efficiency for spincaloritronic applications. We aim to elucidate these effects by performing a comprehensive study of the temperature dependence of LSSE in biphase iron oxide (BPIO = -Fe2O3 + Fe3O4) thin films grown on Si (100) and Al2O3 (111) substrates. A combination of temperature-dependent anomalous Nernst effect (ANE) and electrical resistivity measurements show that the contribution of ANE from the BPIO layer is negligible compared to the intrinsic LSSE in the Si/BPIO/Pt heterostructure even at room temperature. Below the Verwey transition of the Fe3O4 phase, the total signal across BPIO/Pt is dominated by the LSSE. Noticeable changes in the intrinsic LSSE signal for both Si/BPIO/Pt and Al2O3/BPIO/Pt heterostructures around the Verwey transition of the Fe3O4 phase and the antiferromagnetic (AFM) Morin transition

Enhanced Magnetism and Anomalous Hall Transport through Two-Dimensional Tungsten Disulfide Interfaces

“…In addition, from the XRD data, the average crystallite size of Fe 3 O 4 and α-Fe 2 O 3 are estimated to be 115 nm and 55 nm, respectively, based on the Scherrer equation [ 46 ]. The coexistence of Fe 3 O 4 and α-Fe 2 O 3 phases is also confirmed by Raman spectroscopy as reported in our previous work [ 24 ]. High resolution scanning transmission electron microscopy (STEM) confirms the quality of the WS 2 structure with some sulfur vacancies as seen in Figure 1 b.…”

“…In addition, it is essential to understand effects of different phases with different surface terminations of magnetic substrates on TMDs. In this context, we utilize a biphase iron oxide (BPIO = Fe 3 O 4 + α-Fe 2 O 3 ) film, which has recently been explored as an excellent model system for probing the impacts of phase coexistence on spin-thermo transport (via the spin Seebeck effect (SSE)) across heavy metal (HM)/FM interfaces [ 24 ].…”

“…Magnetite, Fe 3 O 4 , is a well-known half metallic ferrimagnetic material with a characteristic transition temperature called the Verwey transition, T V ~120 K. At this temperature, Fe 3 O 4 shifts from a high temperature cubic halfmetallic phase to a low temperature monoclinic high resistance semiconducting/insulating phase due to the freezing of the Fe 3+ and Fe 2+ [ 25 , 26 ]. The half metallic nature above T V with high spin polarization makes it a potential candidate for a variety of spintronics applications [ 24 , 27 , 28 , 29 ]. The transport properties of pure Fe 3 O 4 have been extensively studied [ 24 , 30 , 31 , 32 ].…”

“…The half metallic nature above T V with high spin polarization makes it a potential candidate for a variety of spintronics applications [ 24 , 27 , 28 , 29 ]. The transport properties of pure Fe 3 O 4 have been extensively studied [ 24 , 30 , 31 , 32 ]. In addition to Fe 3 O 4 , different forms of iron oxides exist, such as α-Fe 2 O 3 [ 33 , 34 ], γ-Fe 2 O 3 [ 35 ], ε-Fe 2 O 3 [ 36 ], etc.…”

“…In addition to Fe 3 O 4 , different forms of iron oxides exist, such as α-Fe 2 O 3 [ 33 , 34 ], γ-Fe 2 O 3 [ 35 ], ε-Fe 2 O 3 [ 36 ], etc. Thus, the specific phase transitions associated with multiple phases of iron oxides in a single material may be utilized to probe detectable changes in iron-oxide/TMD heterostructures induced by the MPE [ 24 , 34 ]. The films prepared in this work consist of Fe 3 O 4 and α-Fe 2 O 3 .…”