Annealing and doping effects on magnetism for T\(^{*}\)-type (La, Eu, Sr)\(_2\)CuO\(_{4-y}\)F\(_y\) cuprates

The magnetic behavior of T \(^{*}\) ${}^{\ast }$ -phase cuprates in the underdoped region has been studied through zero-field muon spin rotation/relaxation ( \(\mu \) $\mu$ SR) measurements. By examining the manner in which the superconducting transition temperature changes with increased fluorine substitution, we demonstrate the possibility of achieving an underdoped region in T \(^{*}\) ${}^{\ast }$ -La \(_{1-x/2}\) ${}_{1-x/2}$ Eu \(_{1-x/2}\) ${}_{1-x/2}$ Sr \(_{x}\) ${}_x$ CuO \(_{4-y}\) ${}_{4-y}$ F \(_{y}\) ${}_y$ (LESCOF). For as-grown (AS) samples, the onset temperature for development of spin correlation is determined by \(\mu \) $\mu$ SR measurement. We observed a substantial enhancement from \(\sim \) $\sim$ 7 K (x = 0.18, y = 0) to \(\sim \) $\sim$ 80 K (x = 0.18, y = 0.15) with an appearance of a magnetic order below \(\sim \) $\sim$ 55 K. Thus, the magnetic order can be stabilized by underdoping in AS T \(^{*}\) ${}^{\ast }$ -LESCOF, similar to T-phase La \(_{2-x}\) ${}_{2-x}$ Sr \(_x\) ${}_x$ CuO \(_4\) ${}_4$ . However, the damping of spin precession in the \(\mu \) $\mu$ SR time spectra appears to be significant than in La \(_2\) ${}_2$ CuO \(_4\) ${}_4$ (LCO), suggesting the presence of inhomogeneous magnetism. In addition, the unrecovered normalized time spectrum to 1/3 along the time axis indicates a dynamical nature of magnetism. These magnetic behavior disappears with oxidation annealing, even in the lightly hole-doped sample. The absence of static magnetism in the oxidation-annealed T \(^{*}\) ${}^{\ast }$ -LESCOF could be attributed to the structural effect, as the physical properties of the T \(^{\prime }\) ${}^{\prime }$ -phase cuprates has been discussed in terms of oxygen coordination around the Cu ion.