The structural, dielectric, and magnetic properties of Al 3+ doped Sm 3 Fe 5 O 12 ceramics

The polycrystalline ceramics of Sm 3 Fe 5- x Al x O 12 ( x = 0, 0.5, 1, and 2) are prepared by the sol–gel method. The structure, dielectric, and magnetic properties are studied. The X-ray diffraction patterns indicate that the prepared samples crystallize in garnet phase. All of the samples exhibit relatively high-dielectric permittivity in the low-frequency range. With the increase of Al 3+ content, the dielectric permittivity and the temperature and frequency stabilities at low frequency simultaneously decrease, which suggest the important role of Fe 3+ for the dielectric property. Two sets of dielectric relaxation are observed in the available temperature from 300 to 700 K. With the increase of Al 3+ concentration, the high-frequency relaxation peaks that originate from the carriers hopping between Fe 2+ and Fe 3+ shift toward the direction of low frequency, and the low-frequency relaxation processes that arise from the doubly ionized oxygen vacancies spread to high frequency. By measuring the hysteresis loops and the magnetization-temperature curves, it indicates that the magnetization is decreased and the magnetic property transforms from ferrimagnetism to paramagnetism with increasing the value of x at room temperature. Large permittivity and ferrimagnetic property are observed in Sm 3 Fe 5 O 12 and they are decreased via Al 3+ doping, reflecting the crucial role of Fe 3+ for the high performance.