Magnetism in UCu2Ge2: The role of intrinsic domain wall pinning

We present the de magnetization measurements in the temperature range 5-300 K and field range +/-5 T, on well annealed polycrystalline samples of UCu2Ge2 for which neutron diffraction, neutron depolarization and ac susceptibility have been recently reported by Yusuf, Rao and Raj. These studies are aimed at resolving the controversies regarding the low-temperature magnetic phase of this intermetallic compound. Magnetization is found to be irreversible, at low temperatures, even under an external field of 5 T. The temperature (T-irr) at which the zero-field-cooled and the field-cooled magnetization curves deviate from each other is found to be field dependent. Further, the field-cooled magnetization measurements do not show any loss of magnetization down to the lowest temperature, even under very low applied fields. These findings, together with the hysteresis loop measurements, completely rule out antiferromagnetic ordering or cluster-glass and spin-glass freezing at any temperature. The observed magnetization is found to be highly sensitive to both the cooling rate and cooling in extremely small magnetic fields, such as the Earth's magnetic field. It is also found that, at low fields (about +/-1 mT), zero-field-cooled magnetization is nearly independent of temperature and held. Field-dependent studies show a cross-over of the virgin magnetization curves, at higher fields. All these characteristics and other reported metastable magnetization features have been ascribed to the intrinsic domain wall pinning in this highly anisotropic material. In agreement with our earlier findings, canting of ferromagnetically coupled spins is indicated below about 30 K.