Magnetic properties of UPt single crystals

Several tiny single crystals of UPt have been prepared and examined by mean s of magnetic-susceptibility and magnetization measurements. It is shown th at UPt, which forms in the monoclinic crystal structure, is ferromagnetical ly ordered below about 29K. Our studies, with the magnetic held applied alo ng 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-temperat ure magnetic properties can be explained only by the presence of an energy gap (similar to 40 K) in the dispersion relation of the ferromagnetic magno ns which leads to an exponential temperature dependence of the magnetizatio n.