99Ru Mossbauer effect measurements in Superconducting/Antiferromagnetic Gd 1212 and Ferromagnetic Gd1212 Rutheno-Cuprates

99Ru Mossbauer measurements have been made on Gd1212 samples prepared at the New Zealand Institute for Industrial Research and at the University of Houston. The NZ samples have been shown to be superconducting below 40K by SQUID measurements and antiferromagnetic below 130K by neutron diffraction measurements.SQUID measurements at the Magnet Laboratory in Florida on the Houston sample show that it is not superconducting and ferromagnetic below 130K. Interestingly, the Houston sample shows a clear Mossbauer spectrum at 4.2K. This spectrum shows a 59T hyperfine magnetic field and a non-cubic environment for the Ru nucleus. The isomer shift(IS) is about -0.1 mm/s referenced to Ru powder. This indicates either a +4 or +5 state. Previous 99Ru Mossbauer measurements made on the NZ samples at the same temperature indicate all the same Mossbauer parameters except that the spectrum is not clearly resolved. The mechanism that causes the difference in states between the samples is also unclear. However, the Mossbauer spectra seem to indicate that some multiple lines may exist which causes a broadening of spectrum lines in the NZ samples. If the poor crystal scenario is ruled out, then the unclear spectrum can be due to multiple valence states(+4 or +5) or a spatially variable electric field gradient.The RuO octahedra have been shown, from neutron diffraction and synchrotron measurements to rotate about the c axis. Inhomogeneity in these RuO octahedral rotations or distortions could be linked to the unexpected appearance of superconductivity and magnetism in the NZ samples.