Effect of La3+ substitution on structural, microstructure, magnetic properties, and microwave absorbing ability of yttrium iron garnet

Synthesis and characterization of lanthanum-doped yttrium iron garnet (YIG) in the compositional series of Y3–xLaxFe5O12 (x = 0.0, 0.1, 0.3, and 0.5) were carried out. All compositions were made by using solid state reaction method with ball-milling technique. The phase formation, surface morphology, magnetic properties, and microwave absorbing ability of all compositions were characterized by using an X-ray diffractometer, a scanning electron microscope, a vibrating sample magnetometer, and a Vector network analyzer. The results reveal that all compositions are crystallized into Y3Fe5O12 phase (space group Ia-3d (230). It was observed that the lattice constant is increased from 1.2373 to 1.2421 nm with the increase of lanthanum substitution level from x = 0.0 – 0.5. The crystallite size of Y3–xLaxFe5O12 series calculated by Scherrer method is found to decrease from 78 nm in x = 0.0–63 nm in x = 0.5. The particle size distribution from the surface morphology image analysis is shifted to lower-range number with the increase of lanthanum substitution level from x = 0.0 to 0.5. The substitution process also affects the lattice distortion in La-doped samples and changes the bond angles and bond lengths of the YIG structure. As the results, a linear correlation between the Fe'–O–Fe bond angle with magnetic properties parameters of saturation magnetization (Ms) and remanence magnetization (Mr) was studied. Due to the lanthanum substitution process, all La3+-doped samples possess higher Ms and Mr values compared to the original composition. The results of Vector network analyzer show that the improvement of the Ms and Mr plays an important role in enhancing the microwave absorbing ability of the materials. The minimum RL changes from −8.22 dB (∼ 85.22% microwave absorption) in x = 0.0 to −14.21 dB (∼ 96.25% microwave absorption) in x = 0.5. The enhancement is mainly ascribed to the natural magnetic resonance loss and dipole-polarization loss due to the substitution process. The decreasing particle size also enhances the microwave absorbing ability of the La-doped samples via multiple-reflections mechanism.