Magnetic properties of Co–Al, Ni–Al, and Mg–Al hydrotalcites and the oxides formed upon their thermal decomposition

The magnetic behaviour of Co–Al, Ni–Al, and Mg–Al hydrotalcites (HTlc) with a M2+/Al3+ molar ratio of 3 and carbonates in the interlayer, as well as the mixed oxides obtained after calcination at 823 K for 5 h, has been investigated by DC and AC magnetic susceptibility measurements and isothermal magnetisation. The samples were also characterised by ICP-OES and XRD. The magnetic measurements show that Co–Al and Ni–Al HTlcs behave as ferromagnets, with ordering temperatures of approximately 6–7 K in both cases, and displaying hysteresis loops at 2 K with coercive fields of 4.2 and 5.5 mT, respectively, whereas the Mg–Al-HTlc shows the expected diamagnetic behaviour. A solid solution of cobalt spinels was the decomposition product of Co–Al-HTlc. NiO and MgO were the only crystalline phases identified in the decomposition products of Ni–Al- and Mg–Al-HTlcs, respectively. The magnetic measurements of the decomposition products confirm these data.