Magnetic hysteresis and domain states in Li1+ substituted Ni–Zn ferrites

Compositions of Ni_0.32Zn_0.68-2xLi_xFe_2+xO₄ with x=0.0, 0.025, 0.050, 0.075, 0.100, 0.125, 0.150, 0.175, 0.200 were prepared by oxalate precursors. The M_s–T curves resemble type R. The magnetic moment (n_B) values were found to increase with increase of Li¹⁺ content up to x=0.175, and thereafter it decreased. The former explained on the basis of the exchange interactions, whereas the decrease of n_B is related to the migration of Ni to tetrahedral (A) sites. There is a decrease in Yafet–Kittle (Y–K) angles at octahedral (B) sites, suggesting that lithium does not favor H_c canting. Actually, Li¹⁺ tends to reduce canting, resulting in the increase of n_B coercive force (H_c) and remanance ratio (R) variations have been related to increase of anisotropy constant (K_l) with increasing Li¹⁺ content. The values of R are comparable with the theoretical value, 0.87, which is probably due to the very high density of the samples. Thermal variations of H_c and R reveal that neither parameter changes rapidly with increasing temperature, indicating that the material contains multi-domain (MD) grains in predominance. These results are also supported by a.c. susceptibility studies. The values of wall susceptibility are higher than those of rotational susceptibility, suggesting that the susceptibility is contributed mainly by the domain wall motion.