Anisotropy of the in-plane angular magnetoresistance of electron-doped Sr1-xLaxCuO2 thin films

Signatures of antiferromagnetism (AF) in the underdoped Ln(2-x)Ce(x)CuO(4) (Ln=Nd, Pr, ...) family are observed even for doping levels for which superconductivity exists. We have looked for a similar property in a different electron-doped cuprate family, Sr1-xLaxCuO2, which consists of CuO2 planes separated by Sr/La atoms, and is exempt of the possible influence of magnetic rare-earth ions. We report in-plane magneto-resistance measurements in the normal state of underdoped, superconducting, c- axis oriented, epitaxial Sr1-xLaxCuO2 thin films. This probe is sensitive to spin arrangement and we find that the in-plane magnetoresistance, which is negative and does not saturate for H <= 6 T, exhibits an angular dependence when measured upon rotating a magnetic field within the CuO2 planes. The analysis reveals a superposition of fourfold and twofold angular oscillations. Both of these increase in amplitude with increasing field and decreasing T and appear below a temperature T-onset, which gets higher with decreasing doping levels. Our results demonstrate that these magnetoresistance oscillations, also observed for the Ln(2-x)Ce(x)CuO(4) (Ln=Nd, Pr, ...) family and attributed to an AF signature, are, without ambiguity, a property of CuO2 planes. Besides, these oscillations vary with doping in an unusual way compared to previous results: fourfold oscillations are essentially present in the more underdoped samples while only twofold oscillations are visible in the less underdoped ones. This intriguing observation appears to be a consequence of spin dilution with increasing doping level.