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

• Published in: Journal of physics. D, Applied physics Applied physics, 2021-06, Vol.54 (22), p.224001
• Main Authors: Latiff, Hawa, Eslava, Gabriel Gomez, Devillers, Thibaut, Yanagihara, Hideto, Dempsey, Nora M, Givord, Dominique
• Format: Article
• Language: English
• Subjects: Physics
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/1361-6463/abe5e1

We analyzed the coercivity of both cubic and tetragonally distorted Co x Cu 1− x Fe 2 O 4 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 α = 0.29 and N eff = −0.01 and α = 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 (∼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.