Magnetic behavior of Ho1Ba2(Cu1 - xFex)3O7 - y

We have carried out dc magnetization (x=0 and 0.05) and ⁵⁷Fe Mössbauer spectroscopy (x=0.05) measurements of Ho₁Ba₂(Cu_1-x Fe_x)₃O_7-y , between room temperature (RT) and 4.2 K. Based on x-ray diffraction results all samples are single phase, and either orthorhombic (x=0) or tegragonal (x=0.05). Magnetization measurements determined the onset T_c to be either 90 K (orthorhombic) or 48 K (tetragonal). Mössbauer spectra between RT and 20 K are nearly identical, each consisting of three superposed quadrupole doublets. As the temperature is lowered below about 10 K the Mössbauer spectra exhibit paramagnetic relaxation. The relaxation time increases by about two orders of magnitude as the temperature decreases from 10 to 4.2 K. No magnetic ordering of the Fe moments was observed.