Investigation of magnetic ordering in UPdAs2by neutron diffraction

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Abstract
Magnetic properties of UPdAs2 were studied by both bulk magnetic measurements and by neutron diffraction. The temperature dependence of the reciprocal magnetic susceptibility 1/ chi shows that UPdAs2 orders antiferromagnetically below 240 K. Above 260 K, 1/ chi exhibits an almost straight-line behaviour with mu eff=2.88 mu B and theta p=51 K. Neutron diffraction experiments confirm the tetragonal space group P4/nmm and yielded refined structural parameters. The magnetic ordering in UPdAs2 is of AF IA type with magnetic moments aligned along the c direction. The magnetic structure consists of a stacking of ferromagnetic (001) sheets with a ++-- sequence along the four-fold axis. The ordered magnetic moment of uranium at 8.7 K amounts to 1.69(5) mu B. The temperature variation of the magnetic (101) peak yields the Neel temperature TN=235 K.