Abstract
The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10 nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip.
Highlights
The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions
It was reported that a spin current perpendicular to an applied temperature gradient can be generated in a ferromagnetic metal (FMM) by the transverse spin Seebeck effect (SSE) (TSSE)[4]
For the most experiments we performed under ambient conditions and using contact tips, we can clearly observe an antisymmetric behaviour of the voltage V with respect to the external magnetic field H which can be addressed to the longitudinal SSE (LSSE) due to an unintended out-of-plane temperature gradient DTz
Summary
The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. An adjacent normal metal (NM) converts the spin current via the inverse spin Hall effect (ISHE)[5] into a transverse voltage V, which is antisymmetric with respect to the external magnetic field H (V(H) 1⁄4 À V( À H), see Fig. 1a) In this geometry, the temperature gradient is typically aligned in-plane (rTx) and can induce a planar Nernst effect (PNE) in FMM with magnetic anisotropy[6] which is due to the anisotropic magnetic thermopower and symmetric with respect to H (V(H) 1⁄4 V( À H)). In principle, all the effects of an LSSE experiment can be present in the TSSE experiment with unintended rTz, proximity Nernst effects and especially parasitic LSSE can be present in NM/FMI bilayers as already mentioned recently[25] This leads to four possible effects which are antisymmetric with respect to the external magnetic field, when the temperature gradient is not controlled very carefully (see Fig. 1c). We observe the influence of out-of-plane temperature gradients when an in-plane temperature gradient is applied intentionally by varying the material, diameter and temperature of the electrical a
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