Nanocrystalline iron-rich intermetallic compounds ${\mathrm{Sm}}_2{\mathrm{Fe}}_{17-x}{\mathrm{Si}}_x$ $(x=0,$ 0.5, 1, 1.5, and 2) were studied by means of x-ray diffraction and Mössbauer spectroscopy coupled with Curie temperature and magnetization measurements. The mechanically alloyed and annealed compounds are single-phase with the rhombohedral ${\mathrm{Th}}_2{\mathrm{Zn}}_{17}$-type structure. The Curie temperature is found to increase with Si content x, whereas the unit-cell parameters, calibrated against Bragg reflections of a standard Si powder that was mixed with our samples, are found to decrease. The magnetic moment per Fe atom, deduced from magnetization measurements at 4.2 K up to 90 kOe, increases with x. The best Rietveld agreement factor favors a preferential occupation of Si on the $18h$ site. These results are corroborated by the Mössbauer spectroscopy measurements obtained from 295 K down to 77 K. The Mössbauer spectra analysis is based on the correlation between the Wigner-Seitz volume and the isomer-shift evolution of each specific site $6c,$ $9d,$ $18f,$ and $18h$ of the $R3\mathrm{}¯m$ structure. For all Si concentrations the magnitude of the hyperfine fields is $H_{\mathrm{hf}}\mathrm{}\left(6c\right)>H_{\mathrm{hf}}\mathrm{}\left(9d\right)>H_{\mathrm{hf}}\mathrm{}\left(18f\right)>H_{\mathrm{hf}}\mathrm{}\left(18h\right).$ The mean hyperfine field decreases with x content.

Co_1−xZn_xFe₂O₄ nanoparticles (0 ≤ x ≤ 1) have been synthesized via a green sol–gel combustion method. The prepared samples were studied using X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman, and magnetic measurements. All samples were found to be single phases and have a cubic Fd-3m structure. EDS analysis confirmed the presence of cobalt, zinc, iron, and oxygen in all studied samples. Raman spectra clearly show that Zn ions are preferentially located in T sites for low Zn concentrations. Due to their high crystallinity, the nanoparticles show high values of the magnetization, which increases with the Zn content for x < 0.5. The magnetic properties are discussed based on Raman results. Co ferrite doped with 30% of Zn produced the largest SAR values, which increase linearly from 148 to 840 W/g_MNPs as the H is increased from 20 to 60 kA/m.

We report the successful synthesis and a complete magnetic characterization of CoFe₂O₄@SiO₂@Au magnetoplasmonic nanoparticles. The CoFe₂O₄ magnetic nanoparticles were prepared using the hydrothermal method. A subsequent SiO₂ shell followed by a plasmonic Au shell were deposited on the magnetic core creating magnetoplasmonic nanoparticles with a core–shell architecture. A spin-glass-type magnetism was shown at the surface of the CoFe₂O₄ nanograins. Depending on the external magnetic field, two types of spin-glass were identified and analyzed in correlation with the exchange field acting on octahedral and tetrahedral iron sites. The magnetization per formula unit of the CoFe₂O₄ core is not changed in the case of CoFe₂O₄@SiO₂@Au nanocomposites. The gold nanoparticles creating the plasmonic shell show a giant diamagnetic susceptibility, dependent on their crystallite sizes.

By carefully controlling the electrostatic interactions between cationic liposomes, which already incorporate magnetic nanoparticles in the bilayers, and anionic gold nanoparticles, a new class of versatile multifunctional nanohybrids (plasmonic magneto-liposomes) that could have a major impact in drug delivery and controlled release applications has been synthesized. The experimental results confirmed the successful synthesis of hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) and polyethylene glycol functionalized (PEGylated) gold nanoparticles (AuNPs). The SPIONs were incorporated in the liposomal lipidic bilayers, thus promoting the formation of cationic magnetoliposomes. Different concentrations of SPIONs were loaded in the membrane. The cationic magnetoliposomes were decorated with anionic PEGylated gold nanoparticles using electrostatic interactions. The successful incorporation of SPIONs together with the modifications they generate in the bilayer were analyzed using Raman spectroscopy. The plasmonic properties of the multifunctional nanohybrids were investigated using UV-Vis absorption and (surface-enhanced) Raman spectroscopy. Their hyperthermic properties were recorded at different frequencies and magnetic field intensities. After the synthesis, the nanosystems were extensively characterized in order to properly evaluate their potential use in drug delivery applications and controlled release as a result of the interaction with an external stimulus, such as an NIR laser or alternating magnetic field.

Band structure calculations have been performed on heavy rare-earths R2Fe17compounds. The iron moments are strongly dependent on the site location and little influenced by the rare-earth partner....

The magnetic properties of nanocrystalline M_xFe_3−xO₄ ferrites with M=Fe, Co, and Zn were investigated. The data support a core–shell model, where the core is ferrimagnetically ordered, and the shell shows a spin glass type behavior. The reduced magnetizations of spin glass components follow an m_g = (1 – b/H^−1/2) field dependence. The b values are strongly correlated with the intensities of exchange interactions. The field dependences of the magnetoresistances of Fe₃O₄ and Zn_xFe_3−xO₄ nanoparticles pellets, experimentally determined, are well described if instead of the core reduced magnetization, commonly used, that of the shell is taken into account. For similar compositions of the nanoparticles, identical b values are obtained both from magnetization isotherms and magnetoresistances studies. The half-metallic behavior of spinel Fe₃O₄ based nanoparticles is discussed comparatively with those of double perovskites.