MAGNETIC-PROPERTIES OF CUBIC NPGA3

The cubic (AuCu3-type) NpGa3 compound shown previously to order AF at T-N approximate to 65 K and to undergo a first-order transition to a f erromagnetic state at T-C approximate to 50 K, was investigated by sin gle-crystal neutron diffraction and in-field Mossbauer measurements. T he new data confirm the earlier conclusions and provide new informatio n on the magnetic behaviour of NpGa3. The wave vector in the AF phase is k = (1/2 1/2 1/2). The magnetic structure (type II) consists of a s imple arrangement of alternating + - + - sheets of ferromagnetic (1 1 1) planes. It is found that the Np moments point along the [1 1 1] dir ection in the ferromagnetic slate, while it is suggested that they sho uld be along the [1 0 0] direction in the AF phase.