0000000000388982
AUTHOR
Sebastian T. B. Goennenwein
showing 8 related works from this author
Origin of the spin Seebeck effect probed by temperature dependent measurements in Gd$_{3}$Fe$_{5}$O$_{12}$
2014
We probe the spin Seebeck effect in Gd$_{3}$Fe$_{5}$O$_{12}$/Pt hybrid structures as a function of temperature and observe two sign changes of the spin Seebeck signal with decreasing temperature. A first sign change occurs at a temperature close to the Gd$_{3}$Fe$_{5}$O$_{12}$ magnetic compensation point at around 280 K. There the spin Seebeck signal changes sign abruptly with unaltered amplitude, indicating that the spin current is mainly caused by the magnetic Fe sub-lattices, which reorient their directions at this temperature. A second, more gradual sign change takes place around the ordering temperature of the Gd sub-lattice in the range of 65-85 K, showing that the Gd magnetic sub-lat…
Origin of the spin Seebeck effect in compensated ferrimagnets
2016
Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garne…
Temperature dependence of the non-local spin Seebeck effect in YIG/Pt nanostructures
2017
We study the transport of thermally excited non-equilibrium magnons through the ferrimagnetic insulator YIG using two electrically isolated Pt strips as injector and detector. The diffusing magnons induce a non-local inverse spin Hall voltage in the detector corresponding to the so-called non-local spin Seebeck effect (SSE). We measure the non-local SSE as a function of temperature and strip separation. In experiments at room temperature we observe a sign change of the non-local SSE voltage at a characteristic strip separation d0, in agreement with previous investigations. At lower temperatures however, we find a strong temperature dependence of d0. This suggests that both the angular momen…
Magnon mode selective spin transport in compensated ferrimagnets
2017
We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a non-monotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by using different metal layers we establish that interface effects play a dominating role. They do not …
Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature
2017
We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usual [Formula: see text] relation well established in the collinear magnet yttrium iron garnet, with [Formula: see text] the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex an…
Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions
2021
Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e. spin-dependent electron scattering), whereas intrinsic (i.e. scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19 and Ni50Fe50 over the frequency range from DC to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory revea…
Spin Hall magnetoresistance in antiferromagnet/heavy-metal heterostructures
2017
We investigate the spin Hall magnetoresistance in thin-film bilayer heterostructures of the heavy metal Pt and the antiferromagnetic insulator NiO. While rotating an external magnetic field in the easy plane of NiO, we record the longitudinal and the transverse resistivity of the Pt layer and observe an amplitude modulation consistent with the spin Hall magnetoresistance. In comparison to Pt on collinear ferrimagnets, the modulation is phase shifted by ${90}^{\ensuremath{\circ}}$ and its amplitude strongly increases with the magnitude of the magnetic field. We explain the observed magnetic field dependence of the spin Hall magnetoresistance in a comprehensive model taking into account magne…
Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy
2018
Understanding the transfer of spin angular momentum is essential in modern magnetism research. A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film. Here, we reveal the initial steps of this spin Seebeck effect with <27fs time resolution using terahertz spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum. Upon exciting the metal with an infrared laser pulse, a spin Seebeck current $j_\textrm{s}$ arises on the same ~100fs time scale on which the metal electrons thermalize. This observation highlights that efficient spin transfer critically relies on carrier multiplication and is driven by conduction electrons scattering …