Size-dependent magnetic properties of CoFe₂O₄nanoparticles prepared in polyol

Abstract

Highly crystalline CoFe(2)O(4) nanoparticles with different diameters ranging from 2.4 to 6.1 nm have been synthesized by forced hydrolysis in polyol. The size can be controlled through adjusting the nominal water/metal molar ratio. X-ray diffraction, transmission electron microscopy, x-ray absorption spectroscopy and (57)Fe Mössbauer spectrometry were employed to investigate the structure and the microstructure of the particles produced. Magnetic measurements performed on these particles show that they are superparamagnetic with a size-dependent blocking temperature. At 5 K, high saturation magnetization (~85 emu g(-1)) approaching that of the bulk was found for the larger particles, whereas a very large coercivity (14.5 kOe) is observed for the 3.5 nm sized particles.

CoFe 2 O 4 magnetic ceramic derived from gel and densified by spark plasma sintering

“…Figure 9 shows the magnetization (M) vs. magnetic field (H) of CoFe 2 O 4 measured at different temperatures: 5 K, 100 K and 300 K. The saturation magnetization M s decreases from 88 A⋅m 2 /kg to 83 A⋅m 2 /kg with increasing temperature from 5 K to 300 K. The value 88 A m 2 /kg of M s at 5K is very close to that reported on the bulk CoFe 2 O 4 (80-93 A⋅m 2 /kg [34]) and higher than that recently observed on nanostructured CoFe 2 O 4 obtained by SPS compaction of powder prepared by coprecipitation or thermolysis (51 A⋅m 2 /kg) [35]. These high values can be considered as a consequence of the contribution of the crystallites smaller than 50 nm [24] or a favourable degree of inversion in the spinel structure [36]. The dependence of the coercive field H c on temperature of CoFe 2 O 4 sintered pellet is shown in Fig.10.…”

“…For this reason, several papers report on the conditions and methods used for the preparation of cobalt ferrite nanopowders, such as: chemical co-precipitation [2], hydrothermal method, microwave synthesis, sol-gel method [20][21][22], complexometric method [23], polyol method [24] and others. The sol-gel route is one of the most efficient methods to prepare ultra-fine particles with a high purity and homogenous composition [23][24][25]. The consolidation of nanopowders to produce dense bodies while maintaining their fine crystallite size is usually difficult by conventional methods such as hot pressing, etc.…”

“…grains and grain boundaries) or from electrical interfaces (electrodes)[17,18,24,25,[30][31][32][33]. The complex impedance plot fromFig.7shows flattened semicircle with two components: the high-frequency arc is usually associated to the bulk (grain cores), while the low frequency arc to the grain boundaries contributions[17, 18, 24- 25].…”

Water dispersible CoFe2O4 nanoparticles with improved colloidal stability for biomedical applications

“…The magnetic properties of the nanoparticles can be tuned by controlling its size [4], composition [5], shape [6] and strain/defects [7]. By carefully reducing its size below to a critical diameter, the magnetic nanoparticles can be turned to superparamagnetic nanoparticles.…”

Size Control and Magnetic Property Trends in Cobalt Ferrite Nanoparticles Synthesized Using an Aqueous Chemical Route

“…al"s method [16] which is helpful in synthesizing high specific surface area CoFe 2 O 4 . The reported method is a green, and viable alternative to other synthesis techniques currently used which (among others) 4 include sol-gel [17], forced hydrolysis [18], combustion [19], micro-emulsion [20], mechano-chemical [21], and redox methods [22].…”