Evidence of magnetically driven structural phase transition in RFeAsO (R=La, Sm, Gd, and Tb): A low-temperature x-ray diffraction study

We report measurements of structural phase transition of four parent compounds RFeAsO (R=La, Sm, Gd, and Tb) by means of low-temperature x-ray diffraction (XRD). Magnetic transition temperatures associated with Fe ions (T(N1)) are also determined from the