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Zusammenfassung:
We report the results of magnetic susceptibility, magnetoresistance, specific heat, and neutron-powder- diffraction measurements on U2PdGa3 and U2PtGa3. The investigated compounds crystallize in the orthorhombic CeCu2- type structure (space group Imma) and, at T(N)approximate to30 K, undergo an antiferromagnetic state with finite magnetic correlation lengths 120-150 Angstrom. The magnetic structure is collinear and with the uranium magnetic moments aligned parallel to the orthorhombic c axis. At 1.4 K, the uranium magnetic moments are estimated to be about (0.3-0.4)mu(B)/U. Despite showing the signature of three-dimensional almost long- range antiferromagnetic order below 30 K in the dc-magnetic susceptibility, for both compounds a discontinuity in the specific heat at their Neel temperatures is lacking. Furthermore, the dc-magnetic susceptibility displays magnetic- history phenomena, while the magnetoresistance data indicate the existence of Kondo interactions in the magnetically ordered state. We discuss the observed magnetic behavior in terms of a competition between randomness, Kondo and magnetic exchange interactions.