MAGNETISM IN UCU2GE2 - THE ROLE OF INTRINSIC DOMAIN-WALL PINNING

We present the de magnetization measurements in the temperature range 5-300 K and held range +/-5 T, on well annealed polycrystalline sample s 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 l ow-temperature magnetic phase of this intermetallic compound. Magnetiz ation is found to be irreversible, at low temperatures, even under an external field of 5 T. The temperature (T-irr) at which the zero-held- cooled and the held-cooled magnetization curves deviate from each othe r is found to be field dependent. Further, the held-cooled magnetizati on measurements do not show any loss of magnetization down to the lowe st temperature, even under very low applied fields. These findings, to gether with the hysteresis loop measurements, completely rule out anti ferromagnetic ordering or cluster-glass and spin-glass freezing at any temperature. The observed magnetization is found to be highly sensiti ve to both the cooling rate and cooling in extremely small magnetic fi elds, such as the Earth's magnetic held. It is also found that, at low fields (about +/-1 mT), zero-field-cooled magnetization is nearly ind ependent 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 h ave 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.