Negative magnetization, magnetic anisotropy and magnetic ordering studies on Al3+-substituted copper ferrite

Detailed magnetic properties of Al3+-modified CuFe2O4 spinel ferrite system: CuAlxFe2−xO4; x = 0.0, 0.2, 0.4 and 0.6, have been studied by means of X-ray powder diffraction, field cooled (FC) and zero field cooled magnetization (ZFC) (H = 10 mTesla, T = 4–325 K), magnetic hysteresis (Hmax = 2 Tesla, T = 10 and 300 K) and low field (40 A/m) ac susceptibility (T = 300–750 K) measurements. The system exhibits canted spin structure. It has been shown that the observed features of the FC–ZFC magnetization and ac susceptibility curves arise due to the low magneto crystalline anisotropy, not due to the cluster spin-glass-like magnetic ordering. The interesting features like low temperature cusp in the ZFC magnetization for all the compositions and negative magnetization for x = 0.6 composition have been observed. An attempt has been made to explain the negative magnetization within the framework of available models.

Temperature dependence of MFC and MZFC of Cu–Fe–Al–O system. Inset shows the expanded version of the ZFC mode near the magnetic transition.Figure optionsDownload as PowerPoint slideResearch highlights
► The materials under study are low anisotropy materials with canted spin structure.
► The anomaly on the ZFC curves is due to coexistence and interplay between ferrimagnetic long range ordering and short range ordering.
► The negative magnetization is due to copper moment with a net effect antiparallel to that of the Fe3+ ions but with different temperature dependence.