RESUMO
Nanocrystalline Ce-substituted yttrium iron garnet (YIG) powders of different compositions, Y3-x Ce x Fe5O12 (0 ≤ x ≤ 2.0), were synthesized by a combination of sol-gel auto-combustion and solid-state synthesis techniques. The as-obtained powder samples were sintered at 1150 °C for 10 h. The garnet structure formation is confirmed by the X-ray diffraction pattern, which shows that the calculated lattice parameter increased for x = 1.0 and shows a decreasing trend for x ≥ 1.0 with the addition of cerium ions. The lattice parameter increased from 12.38 Å to 12.41 Å for x ≤ 1.0 whereas it decreased from 12.412 Å to 12.405 Å with the cerium composition for x > 1.0. The average particle size determined by high resolution transmission electron microscopy is in the range of 50 to 90 nm and found to increase with the substitution of cerium ions in YIG. The room temperature magnetic parameters such as saturation magnetization, coercivity and remanence magnetization are greatly affected by the substitution of cerium ions. The values of saturation magnetization decrease from 25.5 to 15 emu g-1 whereas coercivity increases from 1 to 28 Oe with the substitution of cerium ions. The pure YIG sample shows polycrystalline nature that changed towards a single-crystal structure leading to a preferred-(100) orientation with the Ce substitution. The change from a ring to a spotty pattern observed in SAED confirmed the crystalline phase transformation and is well supported by HRTEM and magnetic measurements. The behavior of magnetic and electrical properties is well supported by the poly- and single-crystalline nature of YIG and Ce-YIG, respectively. The crystal structure transformation in YIG brought about by Ce substitution could unveil enormous opportunities in the preparation of single-crystal materials from their polycrystalline counterparts.
RESUMO
In this work a series of Co0.7Cu0.3Cr0.5La(x)Fe1.5-(x)O4 were synthesized via sol-gel auto-combustion technique through the incorporation of La3+ into the raw powders. The structural magnetic and resistivity properties of the synthesized Co-Cu-Cr-La ferrites were investigated. X-ray diffraction data indicated that, after La3+ doping, samples consisted of the main spinel phase in combination with a small amount of a foreign LaFeO3 phase. The addition of La3+ resulted in the reduction of particle size and an increase of porosity of the synthesized samples. The infrared spectra were recorded on the range from 300-800 cm(-1). The two primary bands corresponding to tetrahedral v1 at 595-605 cm(-1) and octahedral v2 at 389-413 cm(-1) were observed. The octahedral site radii increased rapidly with La3+ substitution while the tetrahedral site radii slowly increased. Deviation from the ideal oxygen positional parameter is found to decrease with La3+ substitution. The saturation magnetization of the samples decreased with the amount of La3+ ions doped and the coercivity shows an opposite trend. La3+ substitution affects the hopping between Fe2+ <-> Fe3+, resulted in increase in resistivity.
