Spin Polarization Compensation in Ferrimagnetic Co1−xTbx/Pt Bilayers Revealed by Spin Hall Magnetoresistance

Rare-earth-transition-metal (RETM) ferrimagnets have received great attention for their small magnetic moments and fast dynamics in the development of next-generation spintronic devices. Here, we study spin Hall magnetoresistance (SMR) in the RETM ferrimagnet and heavy-metal bilayers of ${\mathrm{Co}}_{1\text{\ensuremath{-}}x}{\mathrm{Tb}}_{x}/\mathrm{Pt}$. Anomalous temperature dependence of the SMR is observed, where the SMR changes nonmonotonically and has a valley next to the magnetization compensation temperature. Additionally, we find that the SMR varies significantly for different chemical compositions of ${\mathrm{Co}}_{1\text{\ensuremath{-}}x}{\mathrm{Tb}}_{x}$ alloys. These anomalous behaviors are interpreted as the dramatically altered spin polarization of the ${\mathrm{Co}}_{1\text{\ensuremath{-}}x}{\mathrm{Tb}}_{x}$ layer near the compensation point. By deducing spin polarization from the abnormal temperature dependence of SMR, we provide a convenient way to access spin polarization of the RETM ferrimagnets. These experimental results show implications for tunable spin-current sources of RETM ferrimagnets.