Thickness Dependent Magnetic Reversal in Sr₄Ru₃O₁₀ Nanosheets

While ruthenium oxide Sr₄Ru₃O₁₀ has been studied extensively in the last two decades, the origin of the unusual second magnetic anomaly near T_M~50 K remains elusive. Here, we investigated the thickness-dependent anisotropic magnetoresistance (AMR) of pure and 2% Fe-doped Sr₄Ru₃O₁₀ nanosheets. It was clearly found that the AMR properties in pure nanosheets present thickness-dependent behavior and an unusual reversal near T_M, but Fe-doping nansheet completely suppresses the second anomaly down to low temperatures. Analysis of the data demonstrates that this AMR reversal is caused by the magnetization reversal from the ab plane ferromagnetic order at T>T_M to the c direction at T<T_M due to the competition between the shape anisotropy and the inherent magnetocrystalline anisotropy. Our result suggests that the second magnetic transition in Sr₄Ru₃O₁₀ nanosheets is originated from spin reorientation.