An unexpected gap: Magnetic structures of La₂O₃ (Fe_1-xMn_x)₂Se₂ investigated by neutron diffraction and physical property measurements

We prepared a solid solution of La2O3(Fe1-xMnx)2Se2 and performed elastic neutron diffraction experiments at 2 K, measured the magnetization from 2 to 300 K at 500 Oe and 10 T, and also performed resistivity measurements for selected samples. Our experiments show that atomic disorder and magnetic competition open a gap in the magnetic transition from the AFM3 order (x<0.1) to the AFM1 order (x≥0.3) while the transition from AFM1x (0.3<x≤0.9) to AFM1z (x>0.9) appears to be seamless. The compositions at 0.10<x<0.25 did not show any long-range magnetic order in neutron scattering experiments and are semiconducting to insulating until 2 K. However, material with this composition may be a very interesting candidate for further investigations due to the high degree of magnetic competition in this range of the La2O3(Fe1-xMnx)2Se2 system.