Mn-induced Ferromagnetic Semiconducting Behavior with Linear Negative Magnetoresistance in Sr₄(Ru_1-xMn_x)₃O₁₀ Single...

Triple-layered Sr₄Ru₃O₁₀ is a unique ferromagnet with the central RuO₆ layer behaving differently from two outer layers both crystallographically and magnetically. We report that the partial substitution of Ru by smaller Mn gives rise to modification in crystal structure, electronic and magnetic properties of Sr₄(Ru_1-xMn_x)₃O₁₀. Through the single crystal X-ray diffraction refinement, we find that (Ru/Mn)O₆ octahedral rotation is no longer detectable at x ≥ 0.23, leading to the tetragonal structure. The magnetization measurements indicate the ferromagnetic transition temperature T_C decreases from 105 K for x = 0 to 30 K for x = 0.41, with the reduced magnetic moment as well. Remarkably, Mn doping results in the change of magnetic anisotropy from the easy c axis in x = 0 to the easy ab plane seen in x = 0.34 and 0.41. Such change also removes the ab-plane metamagnetic transition observed in x = 0. Furthermore, the electrical resistivity increases with increasing x showing semiconducting behavior with Δ ~ 10 meV for x = 0.34 and 30 meV for x = 0.41. Under applied magnetic field, the magnetoresistance exhibits negative and linear field dependence in all current and field configurations. These results clearly indicate Sr₄(Ru_1-xMn_x)₃O₁₀ is a novel ferromagnetic semiconductor with exotic magnetotransport properties.