Magnetic properties of UPt single crystals

Several tiny single crystals of UPt have been prepared and examined by means of magnetic-susceptibility and magnetization measurements. It is shown that UPt, which forms in the monoclinic crystal structure, is ferromagnetically ordered below about 29K. Our studies, with the magnetic field applied along the principal crystallographic axes, point to a strong uniaxial magnetic anisotropy. The U moments of 1.0 mu(B) / U are oriented along the unique b axis of the monoclinic structure. Our study suggests that the low-temperature magnetic properties can be explained only by the presence of an energy gap (similar to 40 K) in the dispersion relation of the ferromagnetic magnons which leads to an exponential temperature dependence of the magnetization.