Magnetic susceptibilities of Co- and Ni-doped MgO

Abstract

The temperature dependence (1.7-300 K) of the DC magnetic susceptibilities chi for the systems MpMg1-pO (M=Co,Ni) with p<pc (where pc approximately=0.14 is the percolation threshold) are reported. Two sets of samples were studied for both dopants: two lightly doped samples with p<0.01 and two more heavily doped samples with p=0.06 to 0.12. For the lightly doped samples, results are analysed in terms of contributions from single magnetic ions, exchange-coupled pairs and any contributions from the spin-orbit coupling. For Co2+ in MgO, a contribution from spin-orbit coupling leads to a temperature-dependent magnetic moment ( mu T=3.84 mu B at 5 K to 5.15 mu B at 300 K) and an apparent Curie-Weiss variation, whereas for Ni2+ in MgO, the paramagnetic chi P follows the Curie-law variation. From this analysis, concentrations of the dopants are determined. Further, the temperature independence of chi PB/ chi PA for two doping levels A and B at low concentrations is used to show that any contributions from exchange-coupled pairs are negligible. The more heavily doped samples show non-linear variations of chi P-1 against T, presumably due to contributions from magnetic clusters of different sizes.