Role of NiO in the nonlocal spin transport through thin NiO films on Y$_3$Fe$_5$O$_{12}$

TL;DR

This study investigates how NiO thin films influence nonlocal spin transport on Y3Fe5O12, revealing NiO's active role in thermally induced spin currents and the effects of temperature and magnetic fields.

Contribution

It demonstrates that NiO actively contributes to spin transport, especially thermally induced spin currents, challenging the view of AFM as a passive spin conduit.

Findings

Spin current transmissivity peaks at Néel temperature.

Sign change in local electrically injected signals with temperature.

Thermally generated signals increase below 100 K unaffected by NiO thickness.

Abstract

In spin transport experiments with spin currents propagating through antiferromagnetic (AFM) material, the antiferromagnet is treated as a mainly passive spin conductor not generating nor adding any spin current to the system. The spin current transmissivity of the AFM NiO is affected by magnetic fluctuations, peaking at the N\'eel temperature and decreasing by lowering the temperature. In order to study the role of the AFM in local and nonlocal spin transport experiments, we send spin currents through NiO of various thickness placed on Y$_3$Fe$_5$O$_{12}$. The spin currents are injected either electrically or by thermal gradients and measured at a wide range of temperatures and magnetic field strengths. The transmissive role is reflected in the sign change of the local electrically injected signals and the decrease in signal strength of all other signals by lowering the temperature. The thermally generated signals, however, show an additional upturn below 100$\,$K which are unaffected by an increased NiO thickness. A change in the thermal conductivity could affect these signals. The temperature and magnetic field dependence is similar as for bulk NiO, indicating that NiO itself contributes to thermally induced spin currents.