Field Dependence Of Blocking Temperature Research Articles

Interparticle magnetic interactions and magnetic field dependence of superparamagnetic blocking temperature in ferrihydrite nanoparticle powder systems

In this study, nanoparticles of initial synthetic ferrihydrite have been coated with arabinogalactan. The synthesized series of samples with different degrees of coverage of particles has been characterized by X-ray photoelectron spectroscopy, Mössbauer spectroscopy, transmission electron microscopy and magnetometry. The superparamagnetic blocking temperature decreases monotonically with an increase in the degree of coverage of ferrihydrite particles, which is unambiguously related to the different role of the interparticle magnetic interactions in the investigated powder systems. Analysis of the field dependence of the blocking temperature within the random anisotropy model has shown that an increase in the degree of coverage of ferrihydrite particles leads to a decrease in the size of a cluster in which the behaviors of the nanoparticle magnetic moments are correlated. The results obtained have shown the possibility of effective control of the strength of magnetic interparticle interactions in powder ferrihydrite systems by coating nanoparticles with arabinogalactan.

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

We report the synthesis of phase pure, mono-dispersed Fe3O4 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 Fe3O4 nanoparticles. The magnetization studies reveal the superparamagnetic behavior of the nanoparticles at room temperature. The changes in blocking temperatures (TB) of magnetic nanoparticles with applied magnetic fields (Hap), 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. TB versus H relation follows the equation TB(H)=To(1−(H/Ho))m, i.e. the Neel–Brown model of magnetic relaxation in nanoparticles.

Low-field DC-magnetization study of Ho 3+-doped Mn–Zn ferrite ferrofluid

The physical and magnetic properties of magnetic nanoparticles are crucial for their effectiveness and reliability in biomedical applications. In this article, we report the synthesis of a stable Ho-substituted Mn–Zn ferrite ferrofluid and its physical and magnetic properties. Substitution by rare earth metal plays an important role in determining the magneto-crystalline anisotropy in 4f-3d inter-metallic compounds. Ho 3+ substitution not only enhanced the magnetic anisotropy but also produced strong spin frustration at low temperature. The field dependence of blocking temperature shows H 2/3 dependency in the entire range of field, i.e., 10–700 Oe, indicating the emergence of Ising spins characteristics in the present system.

Field dependence of blocking temperature of single-domain magnetite

Blocking phenomenon of single-domain magnetite was studied in detail by measuring magnetization in a field as a function of temperature. Blocking temperature decreases with the increase of applied field. In addition, blocking temperature spectrum becomes very broad with increasing applied field. These tendencies are in agreement with Néel's single-domain theory. In fact, semi-quantitative agreement between experimental and theoretical blocking temperature spectrum is satisfactory.