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The magnetic ordering in polycrystalline USb, and UBi, is studied by means of neutron diffraction. It is found, that the magnetic unit cell of USb, is twice the size of the chemical cell along the c-axis, with alternating ferromagnetic sheets in the sequence + --+ --. .

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An investigation of Fe7Se8 was undertaken to study the magnetic ordering and phase transitions in this compound. On a sample slowly cooled from 600 °C a superstructure was identified corresponding to the 3c structure found by Okazaki [4]. This is derived from the small Ni-As-type cell by doubling of the a-axis and tripling of the c-axis. Neutron diffraction diagrams were made at several temperatures between 4.2 °K and 493 °K. The unit cell dimensions found were : The space groups C 46 — P62 and C 56 — P64 proposed by Okazaki and Hirakawa [3] are not applicable. A possible space group is P31, with vacancies at (1/2, 1/2, 0) (1/2, 0, 1/3) (0, 1/2, 2/3). The magnetic moments are ferromagnetically aligned within each (0001) sheet and antiferromagnetically aligned in neighbouring sheets. At low temperatures the moment direction is perpendicular to the c-axis, but between 120 °K and 130 °K the moments turn to a direction closer to the c-axis. The intensity of the (0003) reflection indicates a tilt of the spin with respect to this axis. No indication has been found of the gradual change in the axis of easy magnetization which was measured by Hirakawa [5] on a torque magnetometer