In tunnel junctions between ferromagnets and heavy elements with strong spin orbit coupling the magnetoresistance is usually dominated by tunneling anisotropic magnetoresistance (TAMR). This makes conventional DC spin injection techniques impractical for determining the spin relaxation time ${\tau }_{\mathrm{s}}$. Here, we show that this obstacle for measurements of ${\tau }_{\mathrm{s}}$ can be overcome by second-harmonic spin-injection magnetoresistance (SIMR). In the second-harmonic signal the SIMR is comparable in magnitude to TAMR, thus enabling Hanle-induced SIMR as a powerful tool to directly determine ${\tau }_{\mathrm{s}}$. Using this approach we determined the spin relaxation time of Pt and Ta and their temperature dependences. The spin relaxation in Pt seems to be governed by the Elliott-Yafet mechanism due to a constant resistivity $\times \mathrm{spin}$ relaxation time product over a wide temperature range.

• Received 13 December 2016
• Revised 27 September 2017

DOI:https://doi.org/10.1103/PhysRevB.96.134421