Fig. 1: Phase diagram with magnetic structures.
From: Multiple magnetic orders in LaFeAs1-xPxO uncover universality of iron-pnictide superconductors
a Here we present our structural and magnetic phase diagram. Neutron diffraction from WISH was used to identify the magnetic structures, while muon spin relaxation (µSR) at EMU was performed on the same samples to identify the transition temperatures, due to much faster counting time for µSR. As x increases, the system’s magnetic order evolves from two-fold symmetric with moments along a, \({C}_{2M}^{a}\), to four-fold symmetric with moments along both a and b, \({C}_{4M}^{{ab}}\), to four-fold symmetric with moments out-of-plane along c, \({C}_{4M}^{c}\), for which the structure can be visualized in b. The single-Q structure with orthorhombic symmetry in \({C}_{2M}^{a}\) becomes a double-Q structure in \({C}_{4M}^{{ab}}\) as the nuclear structure adopts a tetragonal symmetry. The diagonal moments in the \({C}_{4M}^{{ab}}\) order are a consequence of a superposition of two orthogonal “copies” of the \({C}_{2M}^{a}\) that arise as the system becomes tetragonal so that the lattice parameters a and b become equivalent. Likewise, the \({C}_{4M}^{c}\) is a result of two parallel “copies” of out-of-plane spin density waves that constructively and destructively interfere to produce the magnetic pattern seen, where half of the sites have a double moment, and the other half have none. Superconducting transition temperatures were determined by the global minimum in the 2nd derivative of magnetic susceptibility measurements performed on a Quantum Design MPMS.
