Intriguing magnetic and electronic behaviors in La and Ru doped Sr₂IrO₄

We report a detailed experimental study of the structural, magnetic and electrical properties of La and Ru doped (Sr_1-La)₂Ir_1-RuO₄(x= 0.05, 0.15). X-ray diffraction analysis reveals that both samples crystallize in a tetragonal structure with a space groupI4₁/acdwithout impurities. Substitution with La and Ru leads to an increase in the lattice parameteraand a decrease inc. With increasing doping concentration, the Ir-O-Ir bond angle increases while the Ir-O bond length decreases. X-ray photoelectron spectroscopy (XPS) shows that Ir has Ir³⁺(5d⁶) and Ir⁴⁺(5d⁵) charge states, where the Ir⁴⁺charge state decreases with an increase in doping concentration. Thedcmagnetic susceptibilityχ(T) ofx= 0.05 reveals a transition from paramagnetic to weak ferromagnetic (wFM) atT_C∼ 229 K, arising from the canted antiferromagnetic (AFM) spin arrangement. The magnetic ordering temperatureT_Cremains unaltered for higher doping, whereas the magnetic moment is significantly reduced. The analysis of real and imaginary components ofacsusceptibility data, based on conventional critical slow model, frequency shift per decade and Vogel-Fulcher law, unanimously evidences the existence of reentrant spin-glass behavior (RSG), i.e. the coexistence of weak ferromagnetism and spin glass phases for the lowest doping ofx= 0.05. On the other hand, for higher doping (x= 0.15) of hole and electron, the RSG phase vanishes, leaving only the wFM phase at the same temperature as observed inx= 0.05. This suggests the higher doping of La and Ru does not affect the magnetic order, but removes the disorder between FM and AFM phases. The electrical resistivity (ρ) measurement analysis reveals that both the samples show semiconducting/insulating behavior across the temperature range. Theρof thex= 0.05 sample is lower than that of pure sample Sr₂IrO₄(Bhattiet al 2015 J. Phys.:Condens. Matter27016005), whileρofx= 0.15 shows two orders of magnitude larger than thex= 0.05 sample at low temperatures. The conduction mechanism of both samples is described by the 2D Mott's variable-range hopping model. Our results demonstrate that co-doping of two cation sites generates intriguing, competing hopping and magnetic processes.