Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese–zinc ferrite composites

• Published in: Journal of magnetism and magnetic materials 2012-01, Vol.324 (2), p.161-172
• Main Authors: Babayan, V., Kazantseva, N.E., Moučka, R., Sapurina, I., Spivak, Yu.M., Moshnikov, V.A.
• Format: Article
• Language: English
• Subjects: Coated particle; Conducting polymer; Demagnetizing; Domain walls; Dynamic magnetization process; Ferrite; Ferromagnetic material; Induced magnetic anisotropy; Magnetic anisotropy; Magnetic permeability; Magnetization; MnZn ferrite; Permeability; Polyaniline; Polymer matrix composites; Spectra
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2011.08.002

This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ⁎) dispersion region in polymer composites of manganese–zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn–PU) and polyaniline (MnZn–PANI) are measured in the frequency range from 1MHz to 3GHz in a longitudinal magnetization field of up to 700Ое and in the temperature interval from −20°С to +150°С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ⁎. It is established that, at high frequencies, the μ⁎ of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ⁎ in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn–PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization. ► Polyaniline (PANI) coating significantly changes magnetic properties of MnZn ferrite. ► Coated ferrite exhibits higher coercivity, thermomagnetic stability, and resonance frequency shifts. ► Changes are due to magnetic anisotropy induced through pinning of domain walls by PANI.