Estudo do efeito da substituição do íon Al3+ sobre os mecanismos de polarização e condução na hexaferrita de bário-lantânio tipo-M

Abstract

The study of electrical properties and polarization and conduction mechanisms are important in ferrimagnetic and dielectric materials because the potential for their use in various applications such as: spintronics, multiferroic materials and absorption of electromagnetic radiation also depends on these electrical properties. This research aimed to study the effect of substitution of the \ce{Al^{3+}} ion on the polarization and conduction mechanisms in M-type barium-lanthanum hexaferrite using different phenomenological and theoretical models. Ceramics, with chemical formula \ce{Ba_{0.9}La_{0.1}Fe_{12-x}Al_{x}O_{19}} and cation composition \ce{Al^{3+}} from x = 0.0 to 1.3, were prepared using the conventional ceramic method. Structural and morphological analysis was carried out for all ceramics under study using X-ray diffraction, the Rietveld refinement method, Raman spectroscopy and scanning electron microscopy. Measurements of hysteresis loops and complex permittivity were made using vibrating sample magnetometry and dielectric spectroscopy. The main results revealed the coexistence of two hexaferrite phases with non-centrosymmetric $P6_{3}mc$ and centrosymmetric $P6_{3}/mmc$ spatial groups. The grains presented a hexagonal morphology for both phases with a maximum grain size of 5 $\mu$m. Magnetic properties; \ce{M_{s}}, \ce{M_{r}}, \ce{H_{c}}, \ce{K_{eff}}, \ce{H_{a}}, \ce{\mu_{B}} and magnetic $\chi$ decrease with the increase of the \ce{Al^{3+}} cation. The electrical properties vary with the content of the \ce{Al^{3+}} ion. Values of the relaxation parameters, $\alpha$ and $\beta$, obtained through the relaxation process and Havriak-Negami dielectric function, showed non-Debye type relaxation and relaxation time distribution with high asymmetry. The activation energy values determined using the Arrhenius relationship on the relaxation time in the permittivity, electrical modulus and ac-conductivity formalisms indicated polarization and conduction processes in the different temperature ranges analyzed. A local dipolar polarization mechanism and conduction mechanisms; Correlated barrier electron hopping and non-overlapping small polaron tunneling have been identified in the temperature range of 10 to 100 K. A mechanism of interfacial polarization and conduction mechanisms; Quantum mechanical tunneling and tunneling of large overlapping polarons have been identified in the temperature range 110 to 300 K. The activation energy varies with temperature and is related to the polarization and conduction mechanisms identified in each temperature range.