Magnetic phase transitions in nanostructures with different cluster orderings

Magnetic properties of monodisperse nanomagnetite

“…For a description of the first order magnetic phase transition in a nanostructure on the basis of monodis perse magnetite, it is reasonable to apply the thermo dynamic approach, which was developed earlier for isolated nanoclusters with dimensions from 2 to 3 nm [10], for nanostructures formed at the beginning of agglomeration of nanoclusters with dimensions from 30 to 50 nm [11] and for the micellar template cluster organized nanostructure [12]. The Curie (Neel) tem perature in this model depends on the volume change [12] according to the formula…”

“…The Curie (Neel) tem perature in this model depends on the volume change [12] according to the formula…”

Excitation Spectrum of the Néel Ensemble of Antiferromagnetic Nanoparticles as Revealed in Mössbauer Spectroscopy

“…Meanwhile, a quantum-mechanical model for describing thermodynamic properties of an ensemble of ideal (compensated) antiferromagnetic nanoparticles is recently developed [7,8]. This model clarifies principally the difference in thermodynamic behavior of ferromagnetic and antiferromagnetic particles revealed in spectroscopic measurements without the assistance of uncompensated magnetic moment and describes qualitatively macroscopic quantum effects earlier observed repeatedly in experimental Mössbauer absorption spectra of antiferromagnetic and even ferrimagnetic nanoparticles [9][10][11][12][13]. It was also shown that taking the uncompensated spin in the account does not change the qualitative pattern of these effects but is reduced to small numerical corrections of the shape of the absorption spectrum of the ensemble of antiferromagnetic particles [14].…”

“…The continuous energy spectrum of nutations of magnetizations of sublattices accompanying the normal modes of their regular precession for ideal antiferromagnetic nanoparticles has been recently described in [22]. In fact, the presence of the excitation branch corresponding to one of the ferromagnetic normal modes with the local energy minimum for the vectors of sublattice magnetizations precessing in the equatorial plane and nutations of magnetizations accompanying this normal mode gives the phenomenological explanation of macroscopic quantum effects observed in Mössbauer absorption spectra [9][10][11][12][13] and described in the quantum-mechanical model of antiferromagnetic nanoparticles [7,8,14].…”

Magnetic properties of monodisperse nanomagnetite

“…Earlier this approach was applied to 2-3 nm isolated nano clusters [10], to 20-50 nm defective nanostructures [11] and to 10 nm micelle template nanoorganized structures [12]. In order to describe magnetic proper ties of monodisperse magnetite nanostructure we apply the model of the first order magnetic phase tran sition, taking into account an influence of defects and strains in nanocluster, and the presence of developed surface [11].…”