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

AbstractThe magnetic behavior of T$$^{*}$$ ∗ -phase cuprates in the underdoped region has been studied through zero-field muon spin rotation/relaxation ($$\mu $$ μ 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$$^{*}$$ ∗ -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 $$\mu $$ μ SR measurement. We observed a substantial enhancement from $$\sim $$ ∼ 7 K (x = 0.18, y = 0) to $$\sim $$ ∼ 80 K (x = 0.18, y = 0.15) with an appearance of a magnetic order below $$\sim $$ ∼ 55 K. Thus, the magnetic order can be stabilized by underdoping in AS T$$^{*}$$ ∗ -LESCOF, similar to T-phase La$$_{2-x}$$ 2 - x Sr$$_x$$ x CuO$$_4$$ 4 . However, the damping of spin precession in the $$\mu $$ μ 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$$^{*}$$ ∗ -LESCOF could be attributed to the structural effect, as the physical properties of the T$$^{\prime }$$ ′ -phase cuprates has been discussed in terms of oxygen coordination around the Cu ion.