Investigation of the structural, magnetic, impedance properties in samarium-doped yttrium iron garnet

Abstract

Y3-xSmxFe5O12 (x = 0, 1, 2, 3) ferrites with pure single phase were prepared by sol-gel method. The effects of Sm3+-substitution on crystal structure and magnetic properties were systematically investigated. The Sm3+ ions substitution in Y3+ sites resulted in lattice expansion and structural distortion by changing Fe[a]-O-Fe(d) bond length and bond angle, which further modified the magnetization properties and led to the decrease of saturation magnetization by regulating super-exchange interaction between tetrahedron and octahedron sites. The relationships between complex impedance with frequency and temperature were studied, suggesting that asymmetric and depressed semicircle spectrum is owing to a non-Debye like relaxation process controlled by thermal vibration charge carriers, and the electrical conduction within grains is dominated by the charge carrier transition between Fe3+ and Fe2+ sites due to the ionization effect of oxygen vacancies. By fitting the equivalent circuits, it was found that grain boundary and grain have different contributions to complex impedance spectrum while grain boundary relaxation play the dominant role at higher temperature. The slope anomalies of relaxation frequency and conductivity were observed near the ferromagnetic transition temperature (TC) owing to the magneto-electric coupling effect, revealing that magnetic ordering has a great influence on electrical conduction. Ac conductivity analysis reveal that the main conduction mode experiences a gradual transition from a small polaron hopping model (T < 550K) to an overlapping large polaron tunneling model (T > 550K). Moreover, the increase in conductivity is ascribed to two factors: the thermally assisted charge carrier hopping and the ionization effect of oxygen vacancy due to the incorporation of Sm ions.