5. Magnetic order and magnetic history effects in Th(Cosub(x)Nisub(1-x))5

A study was made of the crystallographic and magnetic properties of Th(Cosub(x)Nisub(1-x))5. The samples were annealed at 1100degC during three days and subsequently quenched. X-ray diffraction showed them all to have CaCu5 structure. Virgin samples exposed to an increasing magnetic field show a very slow increase in magnetization until, at a certain value of the applied field, they jump to the ferromagnetic state; this process is irreversible. If a virgin sample is placed in a constant field, Hsub(f), and the temperature is raised, the jump occurs at a temperature Tsub(f) which is better defined the higher the Hsub(f); and Hsub(f) x Tsub(f) is about constant. With x greater than or equal to 0.8, the compounds brought to this state behave like ordinary ferromagnets for which the Curie temperatures could be easily determined. Around x = 0.8, Tsub(c) is a very sensitive function of x. Neutron diffraction of virgin samples with x = 7 revealed ferrimagnetic order at 4.2degK, but at room temperature no long range order magnetic scattering was observed