Morphological metamorphosis of magnetic nanoparticles due to the presence of rare earth atoms in the spinel structure: From spheres to cubes

• Published in: Materials chemistry and physics 2019-01, Vol.222, p.217-226
• Main Authors: Parekh, Kinnari, Espinosa, Daniel H.G., Reis, Dennys, de Oliveira, Cristiano L.P., Wlysses, Wagner, Figueiredo Neto, Antônio Martins
• Format: Article
• Language: English
• Subjects: Anisotropy; Atoms & subatomic particles; Colloids; Coupling; Cubes; Iron; Magnetic colloid; Magnetic fields; Magnetic moments; Magnetic permeability; Magnetic properties; Manganese; Nanoparticle; Nanoparticles; Optical properties; Optics; Rare earth elements; Shape effects; Small angle X ray scattering; Solution chemistry; Spheres; Structural analysis; Structure; Synthesis; Thermal energy; Zinc
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2018.10.020

We report the effect of replacement of 5% of the Fe atoms by Ho during the synthesis of magnetic nanoparticles (MNPs) in the original colloidal system composed of Mn, Zn, Fe, O. Without the presence of Ho the MNPs are spherical and, when the Ho is included in the synthesis they change the shape to cubes with rounded edges. Different experimental techniques were used for the structural characterization of both systems. The magnetic characterization of both colloids showed important differences between them on their magnetic response. The magnetic coupling parameter, the blocking temperature and the effective anisotropy constant are bigger in the colloid with cubic MNPs with respect to the one with spherical particles. The magnetization vs. the applied magnetic field (until 10 kOe) did not show saturation behavior in the colloid with cubic particles, differently from the colloid with spherical particles. This result could be explained taking into account the balance between the energy of the magnetic coupling of the field with the magnetic moment of the cubes, and the thermal energy. The result of Small-angle X-ray scattering (SAXS) pattern confirms the effect of shape due to the Ho substitution in MZ sample. SAXS pattern with and without the presence of external magnetic fields shows non-aggregated particles. The nonlinear optical characterization of the colloids revealed that the imaginary part of the third-order optical susceptibility of the spherical particles is about 30% bigger than that of the cubes. •Replacement of 5% Fe by Ho in magnetic nanoparticles changes shape from sphere to cubes.•Magnetic parameters like TB and Keff are bigger with cubic than with spherical MNPs.•Small-angle X-ray scattering (SAXS) confirms shape effect due to Ho substitution.•SAXS pattern with and without magnetic fields shows non-aggregated particles.•Imχ(3) of nonlinear optical method is 30% higher for sphere than that of the cubes.