Influence of Thickness and Interface on the Low-Temperature Enhancement of the Spin Seebeck Effect in YIG Films

Abstract

The temperature-dependent longitudinal spin Seebeck effect (LSSE) in heavy metal ðHMÞ=Y 3 Fe 5 O 12 (YIG) hybrid structures is investigated as a function of YIG film thickness, magnetic field strength, and different HM detection materials. The LSSE signal shows a large enhancement with reductions in temperature, leading to a pronounced peak at low temperatures. We find that the LSSE peak temperature strongly depends on the film thickness as well as on the magnetic field. Our result can be well explained in the framework of magnon-driven LSSE by taking into account the temperature-dependent effective propagation length of thermally excited magnons in the bulk of the material. We further demonstrate that the LSSE peak is significantly shifted by changing the interface coupling to an adjacent detection layer, revealing a more complex behavior beyond the currently discussed bulk effect. By direct microscopic imaging of the interface, we correlate the observed temperature dependence with the interface structure between the YIG and the adjacent metal layer. Our results highlight the role of interface effects on the temperature-dependent LSSE in HM/YIG system, suggesting that the temperature-dependent spin current transparency strikingly relies on the interface conditions.

Probing length-scale separation of thermal and spin currents by nanostructuring YIG

“…Note that this also agrees with the previously reported film-thickness dependence of highmagnetic-field response of thermopower [15][16][17][18] Figure 5 and Table III are shown to discuss the power-law scaling of the temperature dependence of thermal conductivity and thermopower of all the samples. The exponent n is determined by fitting the measured data with a power-law function CT n , where C is the prefactor and T is temperature.…”

Magnetic-field-induced decrease of the spin Peltier effect in Pt/Y3Fe5O12 system at room temperature

“…While (i) is not well experimentally investigated, the existence of the µm-range length scale in the SPE [19] and the similarity between δ SPE and δ SSE suggest the dominant contribution from (ii) as in the case of the SSE [25,30]. In fact, recently, it has been demonstrated that the high magnetic fields reduce the propagation length of magnons contributing to the SSE [30].…”

“…In fact, the SSE thermopower in a Pt/YIG system was shown to be suppressed by high magnetic fields even at room temperature against the conventional theoretical expectation based on the equal contribution over the magnon spectrum [22]. This anomalously-large suppression highlights the dominant contribution of sub-thermal magnons, which possess lower energy and longer propagation length than thermal magnons [23,25,28,30]. Thus, the experimental examination of the field dependence of the SPE is an important task for understanding the SPE.…”

Evidence for the role of the magnon energy relaxation length in the spin Seebeck effect

“…Additionally, phonon-magnon drag has been put into evidence in previous SSE experiments 8,9 , which, again, points to the importance of interactions between magnons and phonons. To the best of our knowledge, no explicit evidence for the effect of this length scale on SSE measurements has been reported to date.Previous articles on thin films using various growth techniques 10,11,12 have shown the SSE signal to increase with increasing YIG film thickness. In this study, we grow a series of 3 Pt|YIG|GGG heterostructures, with YIG thickness varying from 10 nm to 1 μm, using the same growth technique for all films.…”

“…Previous articles on thin films using various growth techniques 10,11,12 have shown the SSE signal to increase with increasing YIG film thickness. In this study, we grow a series of 3 Pt|YIG|GGG heterostructures, with YIG thickness varying from 10 nm to 1 μm, using the same growth technique for all films.…”