Sr-hexaferrite/maghemite composite nanoparticles—possible new mediators for magnetic hyperthermia

Composite nanoparticles with variable ratios of M-type Sr-hexaferrite and maghemite phases were prepared via the sol–gel method employing polyvinylalcohol as the stabilizing agent, followed by thermal treatment at 600 °C for 32–190 min. The measurements in static magnetic field revealed considerable variation of the coercivity and remanence depending on the relative content of the highly magnetically anisotropic Sr-hexaferrite phase. Calorimetric heating experiments were carried out on aqueous gel suspensions under an alternating magnetic field of maximum amplitude Hmax = 15.1–68.4 kA m-1 and frequency ν = 108 kHz. They showed a strong dependence of the heating efficiency on the coercivity and remanence of the composites, with a specific absorption rate (SAR) value ranging from units to tens of W/g(Feferrimagnetic)

New Tc-tuned magnetic nanoparticles for self-controlled hyperthermia

Manganese perovskite nanoparticles of the XRD size in the range of 30–49 nm were synthesized via sol–gel technique employing citric acid and ethylene glycol. Their magnetic properties were investigated in the static and alternating magnetic fields..

Evidence of non-stoichiometry effects in nanometric manganite perovskites: influence on the magnetic ordering temperature

This work tends to evidence that the significant chemical modifications observed in nanometric manganites are not concentrated at the surface of the particles and play a key role on their magnetic properties, especially for the lowest strontium-doping. La1−xSrxMnO3 solid solution with a 27 nm-average crystallite size was prepared via the Glycine Nitrate Process. The evolutions versus x of the Curie temperature (TC) and saturation magnetization of the nanometric solid solution were interpreted taking into account the Goldschmidt tolerance factor, crystallite size, amount of vacancies and the mixed valency of manganese ions. Two distinct populations were distinguished: (i) for x lower than 0.25, the increase of TC with x could be related to the decreasing amount of cationic vacancies that accommodate the substitution at the A-site of the perovskite framework, simultaneously keeping the content of Mn4+% constant; (ii) for x higher than 0.25, the increase of x led to a decrease of the structural distortion, hence favouring orbital overlap and inducing a TC increase. However, when the amount of Mn4+ exceeded the value of ≈35%, competitive superexchange antiferromagnetic interactions were promoted. As a result, the observed behaviour was a compromise between these two competitive tendencies and led to a quasi-constant TC. For x higher than 0.4, the antiferromagnetic interactions became more important, which induced a TC decrease

Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

Unaggregated La(0.82)Sr(0.18)MnO(3+delta) perovskite nanoparticles with a mean crystallite size of 22 nm were successfully synthesized through an aqueous combustion process (Glycine Nitrate Process, GNP) which takes advantage of exothermic, fast and self-sustaining chemical reactions between metal nitrates and glycine as a suitable organic reducing agent. The influence of G/N molar ratio on the phase purity, crystallite size and manganese valency was screened. Fuel-rich conditions were selected to improve chelation of the cations in acidic pH and ensure an accurate control of the cationic composition. Fast calcination was optimized to enhance crystallinity of the nanoparticles and subsequent milling step was performed to favour their desaggregation. The manganite nanoparticles were thoroughly characterized by X-ray diffraction (XRD), elemental chemical analysis, Mohr salt titration and transmission electron microscopy (TEM). According to a process derived from the Stober's method, they were uniformly coated with a 5 nm thick silica shell, as evidenced by TEM, infrared spectroscopy, zeta potential measurements and dynamic light scattering experiments. Preliminary heating experiments in a ac magnetic field showed these core@shell nanoparticles fulfill the requirements for self-controlled magnetic fluid hyperthermia, considering their size (20-70 nm) and their maximum heating temperature (43 degrees C) which is controlled by the Curie temperature of the magnetic cores

Influence of the structure on electric and magnetic properties of La0.8Na0.2Mn1−xCoxO3 perovskites

The influence of the cobalt substitution for manganese ions in the mixed valence perovskites La0.8Na0.2Mn1−xCoxO3 (0<= x <= 0.2) was investigated by X-ray, electric transport and magnetic measurements. The study carried out on sintered polycrystalline samples revealed the rhombohedral..

Search a new core materials for magnetic fluid hyperthermia : preliminary chemical and physical issues

Today the use of nanoparticles based on magnetite Fe3O4 or maghemite γ-Fe2O3 for magnetic fluid hyperthermia (MFH) application is preferred for evident reasons as biocompatibility and easy synthesis. However, they only show moderate heating capacities because their magnetic properties cannot be simply adjusted to a suitable level. A possible improvement of the MFH technique consists in using more complex magnetic oxides such as: (i) cobalt ferrite and derived phases whose magnetic properties depend on the composition and coercivity is essentially controlled by the magnetocrystalline and/or shape anisotropy, (ii) La1−xSrxMnO3 perovskites whose magnetic properties are influenced by the composition and crystallite size, and (iii) SrFe12O19/γ-Fe2O3 composites whose magnetic properties are mainly controlled by the ratio of the respective magnetic phases. Our main results concerning the synthesis of these compounds in the form of submicronic particles, their magnetic properties and their heating abilities are summarized, compared and discussed in this paper

Insulator–metal transition in Nd0.8Na0.2Mn(1−x)CoxO3 perovskites

The electric and magnetic properties of the perovskites Nd0.8Na0.2Mn(1−x)CoxO3 (0less-than-or-equals, slantxless-than-or-equals, slant0.2) prepared by the usual ceramic procedure were investigated. The insulator-to-metal-like (IM) transition, closely related to a ferromagnetic arrangement, was revealed for the composition of x=0.04 and a similar tendency was detected for x=0. The insulating behavior persists down to low temperatures for higher contents of cobalt ions in spite of the transition to the bulk ferromagnetism. The properties are interpreted in terms of the steric distortion, tilting of the Mn(Co)O6 octahedra and the double-exchange interactions of the type Mn3+–O2−–Mn4+and Mn3.5+δ–O2−–Co2+, respectively. Presence of antiferromagnetic domains in the ferromagnetic matrix for the most of cobalt-substituted samples is supposed

Magnetic heating by cobalt ferrite nanoparticles

In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mössbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature