Non-local voltage measurements with wide F/I/N tunnel contacts are strongly affected by generation of circular electric currents

Electric spin injection is routinely tested by non-local voltage measurements in lateral spin-valves. The advantage of this method is the absence of electric current entering the part of the device where the detecting F/N contact is located. Ideally this leads to the independence of the measured Johnson-Silsbee voltage from the contact size and shape. However, it was predicted [1] that if the detecting contact is wide enough, then circular electric currents are excited in it, altering the non-local voltage and making it device geometry dependent. Calculations [1] were performed in the regime of highly transparent F/N boundary. At the same time, modern measurements often use low transparency F/I/N tunnel contacts, in which circular currents should be strongly suppressed. Thus it seems that tunnel contact measurements should conform to the classic Johnson-Silsbee formula. Here we show that while circular electric currents are indeed suppressed by the tunnel barrier, the voltage modifications persist, may be significant, and have to be accounted for in the data analysis.

[1] Ya. B. Bazlaiy and R. R. Ramazashvili, APL 110, 092405 (2017).