Spin Seebeck Effect in Y3Fe5O12/NiO/Pt Thin Film Heterostructures

The spin Seebeck effect (SSE), where a thermal gradient in a ferromagnet generates spin current, has been in the focus of spintronics studies as it is one of the most efficient ways to generate spin currents. Also, antiferromagnets are gaining attention recently due to their properties like zero net magnetization, low magnetic susceptibility and very fast spin dynamics. In this work, we report SSE measured in Y3Fe5O12(YIG) (20 nm)/NiO(2 nm)/Pt (5 nm) structures as a function of temperature (5 K to 300 K) with the YIG magnetized in-plane, using a lock-in technique that probes the response at the first and second harmonic. By varying the current amplitude, magnetic field direction and temperature we characterize the amplitude of SSE in a comparative study with and without antiferromagnetic layer. Our results show that not only is spin transport possible through thin NiO layers but there is also an increase in the SSE effect magnitude at intermediate temperatures (~150 K). We correlate this increase in the SSE magnitude with an increase in the magnetic susceptibility of NiO shown by our XMLD/XMCD measurements. Our results suggest that the SSE can be used to characterize the response of thin antiferromagnetic materials and optimize their spin-transport characteristics.