Coercivity analysis of cubic and tetragonal (Cu,Co) ferrite particles within the global model

We analyzed the coercivity of both cubic and tetragonally distorted CoxCu1-xFe2O4 particles (x = 0.2 and 0.1, respectively) using the global model. According to magnetic viscosity measurements, the size of the activation volumes v(a) increases from around 2000 nm(3) (v(a)(1/3) 13 nm) at 10 K for both samples, to close to 175 000 nm(3) for the cubic sample and 5400 nm(3) for the tetragonally distorted sample at 300 K. The microstructure-related phenomenological parameters obtained from the global model analysis are alpha= 0.29 and N-eff = -0.01 and alpha= 0.39 and N-eff = -0.24 for the cubic and tetragonal samples, respectively. High-resolution transmission electron microscopy images of the tetragonal sample showed that nanograins are connected through a thin amorphous layer (similar to 1 nm), which could account for the intergranular exchange interactions indicated by the negative value of N-eff as well as values of M-r/M-s > 0.5 for such isotropic samples. Low temperature discrepancies are tentatively attributed to magnetic reversal being governed by a local heating process following thermal activation.

Automated summary

The coercivity of cubic and tetragonally distorted Co_xCu_1-xFe_2O_4 particles was analyzed using a global model, with activation volumes and microstructure-related parameters obtained. High-resolution transmission electron microscopy images showed that nanograins in the tetragonal sample are connected through a thin amorphous layer, explaining the negative N-eff value and M-r/M-s > 0.5.