Spincaloritronic Measurements: A Round Robin Comparison of the Longitudinal Spin Seebeck Effect

Abstract

The rising field of spin caloritronics focuses on the interactions between spin and heat currents in a magnetic material; the observation of the spin Seebeck effect opened the route to this branch of research. This paper reports the results of a round robin test performed by five partners on a single device highlighting the reproducibility problems related to the measurements of the spin Seebeck coefficient, the quantity that describes the strength of the spin Seebeck effect. This work stimulated the search for more reproducible measurement methods through the analysis of the systematic effects.

Measurement of the heat flux normalized spin Seebeck coefficient of thin films as a function of temperature

“…7 However, it has been shown that S∇ T is an unreliable measure of the SSE in thin films due to the presence of thermal interface resistances across the sample stack. 9 To circumvent this problem, Sola et al defined a heat flux based coefficient, 10…”

“…In most studies, a heater is used to establish a temperature gradient across the sample. The temperature difference (ΔT) across the sample stack is usually measured with thermocouples in order to normalize V ISHE as 8,9 S ∇T = (…”

Strong Crystallographic Influence on Spin Hall Mechanism in PLD-Grown IrO2 Thin Films

“…In contrast, Qiu et al studied the performance of IrO 2 in a longitudinal spin Seebeck effect (LSSE) device and found it to be significantly lower than that of Pt [26]. In an LSSE experiment, a spin current was excited in a magnetically ordered material (FM) as a consequence of the application of a thermal gradient [27][28][29]. The current consensus is that this spin Seebeck-spin current is transported by the collective excitations of local moments (magnons) [28,30], and it is therefore better studied in insulators where there is no contribution of free carriers to the output.…”

Quantification of the interfacial and bulk contributions to the longitudinal spin Seebeck effect

“…which accounts for the temperature drop in the Pt layer, at the Pt/FM interface, in the FM layer, at the FM/substrate interface, and across the substrate. In this equation, the thermal drops originated by the thermal contacts of the sample with the baths 27 are disregarded, thus the values obtained in the determination of S i and S b are underestimated. However, the quantification of the relative contributions to ∆V ISHE should be unaffected by this systematic error.…”

“…Once the thermal conductivities κ FM and κ S have been estimated in this way, we proceed to the LSSE experiments for different FM thicknesses. It has been shown that variations in the thermal contacts between the sample and the baths are source of error 17,27 ; care was taken to minimize these errors by ensuring that the same heat power sustained a similar ∆T for all samples. Alternatively, other approaches measure the heat flux instead 6,17,36 .…”