Search

The magnetic properties of nano-crystallite cobalt lanthanum ferrite (CoLaFe O) with varied quantities of lanthanum ( x = 0, 0.1, 0.15, 0.2, 0.25, 0.3) prepared by co-precipitation method have been studied by vibrating sample magnetometer (VSM) and LCR meter. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the size, structure, and morphology of the ferrite samples. The average crystallite size varied from 17.83 nm to 49.99 nm. All the samples, although, in nano range, show significant hysteresis. The saturation magnetization (M) values decreased from 60.57 emu/g to 30.15 emu/g. The remanence (M) fell from 10.85 emu/g to 6.39 emu/g. Doping with lanthanum La ions modulates significantly the magnetic properties of cobalt spinel ferrites without sacrificing the ferromagnetic character. [ABSTRACT FROM AUTHOR]

A detailed study of the magnetic properties of colloidal Ni nanoparticles (∼5.2 nm) that do not present long range order is presented. Two magnetic contributions were observed at high temperatures (>25 K), a dominating paramagnetic one and a ferromagnetic contribution, detected by ferromagnetic resonance and low field magnetic measurements. Interestingly, the ferromagnetic behavior does not follow a classical superparamagnetic description. The effective anisotropy increases at low temperatures due to interactions among the ferromagnetic clusters, which leads the system to a frustrated state. [ABSTRACT FROM AUTHOR]

The model recently proposed by M.A. Chuev [JETP Lett. 85, 611 (2007)] has been analyzed. It has been shown that the anisotropy corrections near the blocking temperature always lead to a magnetization lower than the equilibrium value, contrary to the findings in Chuev’s work. In addition, the asymptotic high-temperature limit of Chuev’s model is inconsistent with the expected thermodynamic limit. Moreover, even at a low temperature, only a careful implementation of this theory can guarantee arriving at the correct result, avoiding some wrong conclusions in Chuev’s work. [ABSTRACT FROM AUTHOR]

Size effect on the internal magnetic structure has been investigated on weakly interacting magnetite (Fe3O4) nanoparticles by ferromagnetic resonance experiments at 9.5 GHz as a function of temperature (4–300 K). A set of three samples with mean particle size of 2.5 nm, 5.0 nm and 13.0 nm, respectively, were prepared by chemical route with narrow size distribution ( σ < 0.27). To minimize the dipolar interaction, the particles were dispersed in a liquid and a solid polymer matrix at ∼0.6% in mass. By freezing the liquid suspension with an applied external field, a textured was obtained. Thus, both random and textured suspensions were studied and compared. The ferromagnetic resonance experiments in zero-field-cooled and field-cooled conditions were carried out to study the size effect on the effective anisotropy field. The dc magnetization measurements clearly show that the internal magnetic structure was strongly affected by the particle size. [ABSTRACT FROM AUTHOR]

100 MeV Si+7 irradiation induced modifications in the structural and magnetic properties of Mg0.95Mn0.05Fe2O4 nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles. [ABSTRACT FROM AUTHOR]