Effect of lanthanum ions on magnetic properties of Y3Fe5O12 nanoparticles

Lanthanum ion (La3+)-substituted garnet nanoparticles Y3−x La x Fe5O12 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were fabricated by a sol–gel method. Their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectrum. The XRD results show that samples of Y3−x La x Fe5O12 (0.0 ≤ x ≤ 0.8) are all single phase and the sizes of particles range from 32 to 65 nm. Those of Y2LaFe5O12 consisted of peaks from garnet and LaFeO3 structures. Compared to pure YIG, the saturation magnetization is larger when the La concentration x = 0.2. However, with increasing La concentration (x), it decreases obviously. Meanwhile, may be due to the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased. Different from the pure YIG, the Mossbauer spectra of Y2.8La0.2Fe5O12 and Y2.2La0.8Fe5O12 are composed of four sets of six-line hyperfine patterns. The results tell us that the substitution of La3+ ions with large ionic radius (1.061 A) will give rise to a microscopic structure distortion of the a- and d-sites to different degrees, and the Zeeman sextets from a- and d-sites begin to split into two sub-sextets, which is helpful to explain the phenomenon observed in the study of the magnetic property.