Appearance of superparamagnetism on heating nanosize Mn0.65Zn0.35Fe2O4

Abstract

Nanosize particles (average size ∼12 nm) of mixed ferrite Mn0.65Zn0.35Fe2O4 were prepared by the hydrothermal precipitation route and studied using x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, magnetization measurements, and Mössbauer spectroscopy. The as-prepared sample was largely ferrimagnetic and, as the sample was annealed at temperatures above 250 °C, it gradually became superparamagnetic. This unexpected behavior is explained by assuming that the cation distribution in the nanosize as-prepared sample is in a metastable state and, as the sample is heated, this distribution changes to a more stable state while the grain size remains nearly the same.

Impact of zinc substitution on the structural and magnetic properties of chemically derived nanosized manganese zinc mixed ferrites

“…Hence the increase in T c can be mainly attributed to the non-equilibrium cation redistribution as reported by Kulkarni et al [10] in ultrafine MnFe 2 O 4 particles. Higher degree of inversion was found to be associated with higher T c values in ultra fine ferrite systems.…”

“…In ceramic samples the zinc ions were found to exist only in the tetrahedral sites (A sites) as expected. However, zinc is found to occupy octahedral sites in the case of nanosized manganese zinc ferrites when they are prepared by co-precipitation methods, or the pulsed laser deposition method or the high-energy ball-milling method [10]. The occupancy of zinc ions in octahedral sites in the nanoregime can alter the expected cation distribution to a great extent and will result in modified structural and magnetic properties in the case of Mn 1Àx Zn x Fe 2 O 4 nanoparticles.…”

Structure and magnetic properties of Mg0.35Cu0.2Zn0.45Fe2O4 ferrite synthesized by co-precipitation method

“…On heating, the metastable state irreversibly gets converted to a stable state through redistribution of cations among the A and B sites. [23][24][25] The cation redistribution would consume the activation energy. 24 Eventually, the obtained linear relationship between the ln(D) and the reciprocal of absolute temperature (1/T) was not very good.…”

ZnFe2O4 as a new catalyst in theC-methylation of phenol

“…It consists of mixing and calcining of metal oxides or carbonates of elevated temperature to get the crystalline product. The other methods that have been reported are high-energy ball milling [5], sol-gel method [7], co-precipitation of hydrous oxides from salts solution followed by calcination at high temperatures [8 -10] and hydrothermal routes [11,12] in which interfacial reaction of metal Zn sheet with FeCl 2 as reactant in ammonia solution at 180…”