In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained by a chemical route previously described. This magnetic graphite has been obtained by a vapor reaction consisting of a controlled etching on the graphite structure. By magnetic force microscopy we have verified that its magnetic properties are related to the topographic defects introduced in the pristine material. Also, the magnetic properties have been verified through magnetization measurements as a function of temperature and applied magnetic field. At low temperatures $\left(2\mathrm{K}\right)$ the saturation magnetization reaches a value of $0.58\mathrm{emu}∕\mathrm{g}$, leading to a defect concentration of $1250\mathrm{ppm}$. The system is highly irreversible due to the inhomogeneity of the distribution of defects in the material. Two transition temperatures are detected, $T_{\mathrm{c}1}=115\left(5\right)\mathrm{K}$ and $T_{\mathrm{c}2}=315\left(5\right)\mathrm{K}$. These transitions could be associated to the weak coupling between ferromagnetic regions related to defects and to the ferromagnetism inside the defect regions.

We derive new expressions for the average magnetization loops, M(H), based on the exponential critical state model. The components χ^′ and χ^″ of the complex susceptibility are calculated and an algorithm to fit ac susceptibility data is discussed. This algorithm is employed to study the intergranular response χ^′(H_m) and χ^″(H_m) measured for two samples of YBa₂Cu₃O_7−δ as a function of the ac field amplitude H_m. One sample is a porous sintered cylinder and the other is a very dense melt‐textured bar. In both cases good fits of the calculated components χ^′ and χ^″ are obtained using an algorithm that involves two free parameters, the full penetration field, H_p, and the sample quality factor, p. An interesting result for the melt‐textured sample is the observation of a step in χ^′(H_m) curves at very low H_m, possibly associated with grain clustering.

We report the chemical synthesis route, structural characterization, and physical properties of nanofluid magnetic graphite (NFMG) obtained from the previously synthesized bulk organic magnetic graphite (MG) by stabilizing the aqueous ferrofluid suspension with an addition of active cationic surfactant. The measured magnetization-field hysteresis curves along with the temperature dependence of magnetization confirmed room-temperature ferromagnetism in both MG and NFMG samples.

We have grown high-quality single crystals of the colossal-magnetoresistance (CMR) material ${\mathrm{La}}_{\text{0.7}}{\mathrm{Ca}}_{\text{0.3}}{\mathrm{MnO}}_3$ by using the laser heated pedestal growth method. Samples were grown as fibers of different diameters, and with lengths of the order of centimeters. Their composition and structure were verified through x-ray diffraction, scanning electron microcopy with energy dispersive x-ray analysis and by Rietveld analysis. The quality of the crystalline fibers was confirmed by Laue and electron backscatter diffraction patterns. Rocking curves performed along the fiber axis revealed a half-height width of $\text{0.073°.}$ The CMR behavior was confirmed by electrical resistivity and magnetization measurements as a function of temperature.