Magnetic order and magnetic history effects in ThCo5xNi5–5x

The magnetic properties of several compounds of the series ThCo5xNi5-5x were studied by neutron diffraction and magnetization measurements. For × ≧ 0.8 the compounds are ferromagnets. For lower x-values there is an antiparallel orientation of the 3d moments residing at the 3(g) and 2(c) sites, respectively. There is a slight preference in occupation of the 3(g) sites by Co atoms. Associated with the change in magnetic order type is a discontinuous change in the concentration dependence of the magnetic ordering temperatures. A discontinuous change near × = 0.8 was also observed for the concentration dependence of the lattice constants and the compressibility. All magnetically ordered compounds investigated give rise to a negative pressure dependence of the ordering temperatures. Most of the compounds ThCo5xNi5-5x show very pronounced magnetic history effects in their magnetization versus temperature curves. It is proposed that these effects are due to the presence of narrow Bloch walls in these compounds.