Electrical detection of spin-flip transition in metal/Na5Co15.5Te6O36 heterostructure

Abstract

We report on the longitudinal magnetoresistance (MR) in thin metal films on an Ising-type antiferromagnetic insulator, Na5Co15.5Te6O36 (NCTO). Steep changes in the MR spectra with hysteresis were observed at spin-flip transitions driven by magnetic fields applied along the easy axis of the NCTO crystal. The MR jumps almost follow step-like changes in magnetization at the spin-flip transition. At very low temperatures where Co moments are partially frozen, the MR anomalies exhibit a tunnel-magnetoresistance-like shape. The observed MR anomalies at the spin-flip transition are attributed to strain effects via magnetostriction upon the magnetic-structure change of the Co nets in NCTO, because similar MR jumps are observed in both Pt/NCTO and Cu/NCTO. Interestingly, we found that the high-field slopes of the MR spectra show opposite signs between Pt/NCTO and Cu/NCTO at low temperatures. Because the opposite signs of the high-field MR are prominent below the antiferromagnetic transition temperature of NCTO, the interaction between the interface spin accumulation and magnetization is likely to contribute to the MR effect in the induced ferromagnetic state.