Collapse of the magnetic ordering and structural anomalies in the UxLa1-xSsystem: neutron diffraction and specific heat measurements

We report specific heat and neutron diffraction measurements of seven sampl es in the solid solution system UxLa1-xS. All samples have the simple fee N aCl crystal structure. Both specific heat and neutron diffraction confirm t he suggestion from the earlier magnetic measurements that the ferromagnetis m disappears abruptly at x(c) similar to 0.57. Near x(c) there is a doublin g of gamma the electronic contribution to the specific heat, as compared to the value of 23 mJ mol(-1)K(-2) in pure US. Around x(c) the widths of the nuclear Bragg peaks show a considerable broadening, as well as anomalies in the mean lattice parameter, as compared to those expected from Vegard's la w. A preliminary analysis suggests this broadening may be due to a loss of long range lattice order near x(c). However, these changes are independent of temperature, so that further experiments are necessary before they can b e associated with the changes in magnetic behavior at x(c).