The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La_1−xCa_x)(Zn_1−xMn_x)AsO

We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La_1−xCa_x)(Zn_1−yMn_y)AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature $T_{\text{C}}$  ∼30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, $T_{\text{C}}$ increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that (La_1−xCa_x)(Zn_1−yMn_y)AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La_0.90Ca_0.10)(Zn_0.90Mn_0.10)AsO below 300 K. (paper)