Magnetic Field Dependence of Blocking Temperature in Oleic Acid Functionalized Iron Oxide Nanoparticles

Abstract

We report the synthesis of phase pure, monodispersed Fe 3 O 4 nanoparticles of size ∼10 nm via chemical co-precipitation of ferrous and ferric ions, under controlled pH and temperature. The nanoparticles are oleic acid functionalized and hence dispersible in organic medium. The structure and morphology of nanoparticles are determined by analyzing XRD pattern and TEM micrographs, confirming the formation of phase pure Fe 3 O 4 nanoparticles. The magnetization studies reveal the superparamagnetic behavior of the nanoparticles at room temperature. The changes in blocking temperatures (T B ) of magnetic nanoparticles with applied magnetic fields (H ap ), noted from the cusp of the zero-field-cooled magnetization, the indicate effects of dipole interactions. A decrease in blocking temperature from 95 K to 15 K has been observed on varying the magnetic field from 50 Oe to 5000 Oe. T B versus H relation follows the equation T B (H ) = T o (1 − (H /H o )) m , i.e. the Néel-Brown model of magnetic relaxation in nanoparticles.

Superparamagnetic iron oxide nanoparticles for magnetic hyperthermia: recent advancements, molecular effects, and future directions in the omics era

“…(1) where τ 0 is a characteristic of the material, named attempt time or attempt period (usually between 10 -10 -10 −9 s), K is the anisotropy constant, V is the volume of the nanoparticle, k B is the Boltzmann constant, and T is the temperature. Usually, at temperatures higher than the blocking temperature T B , that is the temperature below which the magnetic moments do not have the required energy to flip directions (for instance, T B is reported to be < 100 K, for oleic-acid stabilised SPIONs of ≈ 10 nm, when no external magnetic field is applied 17 ), and given the measuring times of conventional techniques, the net magnetisation of SPIONs results, on average, equal to zero. As evident from Eq.…”

“…(for instance, T B is reported to be <100 K, for oleic-acid stabilised SPIONs of ≈10 nm, when no external magnetic field is applied 17 ), and given the measuring times of conventional techniques, the net magnetisation of SPIONs is, on average, equal to zero. As is evident from eqn (1), the smaller the nanoparticles, the lower the energy necessary to flip the magnetic moment.…”

“…4 In Néel relaxation, the magnetisation of the single nanoparticle can rapidly flip direction with a characteristic time defined as the Néel relaxation time, τ N , that depends, among other parameters, on the particle size and magnetic anisotropy, and on the temperature of the medium, as expressed by the equation:where τ 0 is a characteristic of the material, named the attempt time or attempt period (usually between 10 −10 and 10 −9 s), K is the anisotropy constant, V is the volume of the nanoparticle, k B is the Boltzmann constant, and T is the temperature. Usually, at temperatures higher than the blocking temperature T B , that is the temperature below which the magnetic moments do not have the required energy to flip directions (for instance, T B is reported to be <100 K, for oleic-acid stabilised SPIONs of ≈10 nm, when no external magnetic field is applied 17 ), and given the measuring times of conventional techniques, the net magnetisation of SPIONs is, on average, equal to zero. As is evident from eqn (1), the smaller the nanoparticles, the lower the energy necessary to flip the magnetic moment.…”

Magnetite (Fe3O4) Nanoparticles in Biomedical Application: From Synthesis to Surface Functionalisation

“…Below this temperature, superparamagnetic MNPs immobilise in the absence of a magnetic field (H) [4]. T B varies between blocked state and superparamagnetic behaviour when H is changed; it possesses an inversely proportional relationship with H [22].…”

Modifications of EHPDB Physical Properties through Doping with Fe2O3 Nanoparticles (Part II)

“…Moreover, the convergence of the ZFC and FC curves was not visible up to 380 K; therefore, both Sample 1 and the nanocomposites were in the blocked state (T B corresponded to the convergence point of both the ZFC and FC curves). It seemed that T B was outside of the measuring range, because we did not use any surfactant to decorate the γ -Fe 2 O 3 nanoparticles, in opposition to Kataby et al, who observed significant T B modifications depending on the surfactant used (e.g., stearic acid shifted T B to 280 K in relation to sulfonic acids, where T B was around 120 K) [ 79 ], as well as Tanwar et al, who showed that decoration of nanoparticles with oleic acid changed T B (from 95 K up to 15 K in the 0.5 T magnetic field) [ 80 ]. It should also be noted that in the case of surfactant-functionalized nanoparticles, the T B depends on the strength of the magnetic field.…”