We report on the longitudinal magnetoresistance (MR) in thin metal films on an Ising-type antiferromagnetic insulator, ${\mathrm{Na}}_5{\mathrm{Co}}_{15.5}{\mathrm{Te}}_6{\mathrm{O}}_{36}$ ($\mathrm{NCTO}$). 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 $\mathrm{NCTO}$ crystal. The MR jumps almost follow steplike changes in magnetization at the spin-flip transition. At very low temperatures where $\mathrm{Co}$ 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 $\mathrm{Co}$ nets in $\mathrm{NCTO}$ because similar MR jumps are observed in $\mathrm{Pt}/\mathrm{NCTO}, {\mathrm{Pt}/\mathrm{SiO}}_x/\mathrm{NCTO}$, and $\mathrm{Cu}/\mathrm{NCTO}$ heterostructures. Interestingly, we find that the high-field slopes of the MR spectra show opposite signs between $\mathrm{Pt}/\mathrm{NCTO}$ and $\mathrm{Cu}/\mathrm{NCTO}$ at low temperatures. Because similar MR spectra are observed for ${\mathrm{Pt}/\mathrm{SiO}}_x/\mathrm{NCTO}$, in which the interface magnetic interaction is negligible, the weak antilocalization due to the strong spin-orbit interaction of the Pt films is likely to contribute to the low-temperature MR.

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• Antiferromagnetism
• Magnetism
• Magnetoresistance
• Magnetostriction
• Weak antilocalization
• Heterostructures
• Magnetic insulators
• Magnetization measurements