Magnetic ordering in U_0.95Th_0.05Cu₂Ge₂

Abstract

The effect of small substitution of thorium in place of uranium in a widely reported compound UCu₂Ge₂ has been investigated using d.c. magnetization, a.c. susceptibility and neutron diffraction techniques. For 5 at.% Th substitution [i.e. U_0.95Th_0.05Cu₂Ge₂] the following changes are observed: (i) The ferromagnetic phase persists down to the lowest temperature, as reported by some of us for the parent compound. However, the ferromagnetic ordering temperature reduces by ∼7 K. (ii) The ordered moment value reduces appreciably below that expected from magnetic dilution effect. (iii) Magnetic anisotropy is very greatly enhanced at low temperatures, e.g. the coercive field (H_c) at 5 K increases by ∼2.7 times that of the parent compound. Furthermore, H_c is found to increase exponentially with decreasing temperature. (iv) The features arising due to the random canting of spins reported for UCu₂Ge₂ over 25–45 K temperature range are completely suppressed by just 5 at.% substitution of thorium in place of uranium. The observed features in the a.c. susceptibility and d.c. magnetization have been ascribed to the magnetic domain wall pinning, arising due to the presence of strong anisotropy at low temperatures.