X-ray absorption spectra and X-ray magnetic circular dichroism studies at Fe and Co L_2,3 edges of mixed cobalt-zinc ferrite nanoparticles: Cationic repartition, magnetic structure and hysteresis cycles

X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) spectra at Co and Fe L_2,3 edges are performed on mixed cobalt-zinc ferrite nanoparticles Co_0.73yZn_0.73(1-y)Fe_2.18□_0.09 O₄ (with y = 0.4, 2.8 and 3.7 nm average diameter; the symbol □ represents a vacancy). Simulation of the spectra thanks to ligand field multiplet theory allows an evaluation of the cationic repartition. Co²⁺ occupies preferentially octahedral sites for the studied composition, its magnetic moment is 3.64 μ_B, consistent with well-known bulk values for pure cobalt ferrite. Hysteresis curves are measured thanks to XMCD spectra and compared to magnetometry measurements. Being chemically selective, XMCD technique is found promising to complete magnetometry measurements on systems involving several magnetic ions.