MAGNETIC, ELECTRICAL, AND SPECIFIC-HEAT PROPERTIES OF UPDSN AND UAUSN

UPdSn orders antiferromagnetically below 40 K and undergoes another magnetic phase transition at about 27 K, which is connected with a re-arrangement of the antiferromagnetic structure. The magnetic properties of UPdSn are strongly anisotropic with the c-axis as the hard-magnetization direction. For UAuSn, the maximum at 36 K in the chi(T) curve may also indicate the onset of antiferromagnetism. However, the verv broad anomaly in the specific heat, the poorly resolved Sn-119 Mossbauer spectra and the magnetic history phenomena at lower temperatures do not point to long-range magnetic order. The possibility of a frozen non-periodic arrangement of U magnetic moments is discussed in connection with atomic disorder within the Au-Sn sublattice. The distinction between the electron properties of UAuSn and UPdSn is reflected in the different values of the gamma-coefficient of the low-temperature specific heat, which is remarkably small for UPdSn (5 mJ/mol K2)in contrast to UAuSn (80 mJ/mol K2). A possible localization of the 5f states in UPdSn is envisaged.