Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)

Specific heat measurements in the temperature region from 2 to 50 K in magnetic field up to 10 T, oriented parallel and perpendicularly to the CoO₂ layers were carried out on a series of high-quality single- crystals of NaxCoO₂ (x = 0.73, 0.76, 0.77, 0.78 and 0.87). Surprisingly, sharp lambda type anomaly was observed only for the concentration x = 0.76 at temperature (21.80 ± 0.02) K, for all the remaining doping levels round anomaly in experimental data was visible at temperature ~ 20 K, indicating a smeared magnetic phase transition. While the magnetic field oriented perpendicularly to the CoO₂ layers shifts the temperature of this anomaly to lower values, parallel magnetic field has no influence on it, what indirectly supports the idea of A-type antiferromagnetic ordering in studied systems

Mechanochemical Preparation and Magnetic Properties of Fe₃O₄/ZnS Nanocomposite

Powder nanocomposite of Fe₃O₄/ZnS was prepared by mechanochemical synthesis in a planetary ball mill. In this reaction natural magnetite mineral Fe₃O₄ was used, together with zinc acetate (CH₃COO)₂Zn·2H₂O and sodium sulfide Na₂S·9H₂O, as precursors for the zinc sulfide ZnS. X-ray diffraction revealed that the sample is composed of small nanocrystalline particles, containing Fe₃O₄ and ZnS. The non-milled magnetite showed distinctive Verwey transition at around 120 K, this becomes suppressed after milling, as a consequence of structural disorder and presence of defects. Moreover, the reduction of saturation magnetization from 91 A m²/kg to 69.2 A m²/kg was observed, as a consequence of the milling process. The magnetization of the Fe₃O₄/ZnS nanocomposite was the lowest (34.5 A m²/kg), due to the milling and to the decreased weight fraction of the ferrimagnetic component. Nevertheless, the Fe₃O₄/ZnS sample demonstrates ferrimagnetic behavior as well, and its structure is less perturbed by milling, the Verwey transition, although less impressive, but is preserved

Thermodynamic and Magnetotransport Properties of High Quality Na0.77CoO2Na_{0.77}CoO_{2} Single Crystals

Heat capacity and electrical resistivity of high-quality $Na_{0.77}CoO_{2}$ single crystals was systematically studied as a function of temperature and magnetic field. Anomalies at 20 K have been observed both in the heat capacity and the electrical resistivity. The broad bump in the heat capacity indicates a smeared magnetic phase transition. Magnetic fields up to 9 T, oriented perpendicularly to the ab plane, reduce the temperature of this anomaly in accordance with the assumption of A-type antiferromagnetic ordering. The low temperature upturn observed in resistivity below 20 K for slow cooling is also suppressed by the magnetic field. This anomaly is probably the consequence of the interplay of several different mechanisms, including the Kondo effect, electron-electron interactions, and electron-phonon scattering

Influence of Annealing Treatment on the Structure and Magnetic Properties of Fe-Al-Cu-Nb-Si-B Alloys

In this paper we present experimental results on influence of Al content on the structure and saturation magnetostriction of Fe-Al-Cu-Nb-Si-B alloys after heat treatment. Transmission electron microscopy observations confirmed the existence of nanocrystalline structure after annealing at 490°C and 550°C for all samples. The crystallization temperature of FeSi phase and the temperature at which the polycrystalline transformation starts were determined from temperature dependence of electrical resistivity. Aluminium slightly decreases the first crystallization temperature and considerably decreases the saturation magnetostriction in as-quenched state

Magnetic Properties of Mechanochemically Synthesized Mixed Oxides

The mixed oxides $Fe_{2}O_{3}-ZnO$ have been obtained in nanocrystalline state by reactive milling in a high-energy planetary mill, from a stoichiometric mixture of hematite and ZnO. The magnetic properties of samples were evaluated by magnetization measurements and Mössbauer spectrometry. A post milling annealing promotes the solid state reaction and improves the zinc ferrite formation, paramagnetic $ZnFe_{2}O_{4}$ phase is formed. Further mechanical activation leads to structural transformation into Wüstite-type (FeZn)O mixed oxide, with ferromagnetic hysteresis and increased magnetization

The comparison of magnetic properties of nanocrystalline Fe-M-Cu-Nb-Si-B (M = Co, Ni) thin films and ribbons

An attempt is made to study the structure and the magnetic properties of the films of Fe-M-Cu-Nb-Si-B (M = Co. Ni) alloys. Thin films have been prepared by ion beam sputtering. The structural observations showed the process of thin film crystallization after annealing. The differences of magnetic domain structure depending upon the heat treatment were observed. The influence of annealing temperature on the coercivity was examined. The minimum of the coercivity was shifted from one annealing temperature of 550°C for ribbons to temperature range 350°C-420°C for thin films and the minimal value of the coercivity of thin films is about 50 times higher than that one for ribbons

Mechanochemically synthesized nanocrystalline Sb2S3 particles.

Nanocrystalline Sb2S3 particles have been synthesized from Sb and S powders by high-energy milling in a planetary mill using argon protective atmosphere. X-ray diraction, particle size analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, electron diraction, high resolution transmission electron microscopy, UV-VIS, and dierential scanning calorimetry methods for characterization of the prepared particles were applied. The powder X-ray diraction pattern shows that Sb2S3 nanocrystals belong to the orthorhombic phase with calculated crystallite size of about 36 nm. The nanocrystalline Sb2S3 particles are constituted by randomly distributed crystalline nanodomains (20 nm) and then these particles are forming aggregates. The monomodal distribution of Sb2S3 particles with the average hydrodynamic parameter 210 nm was obtained. The quantication of energy dispersive X-ray spectroscopy analysis peaks give an atomic ratio of 2:3 for Sb:S. The optical band gap determined from the absorption spectrum is 4.9 eV, indicating a considerable blue shift relative to the bulk Sb2S3. Dierential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300 C, suggesting recovery processes. This interpretation is supported by X-ray diraction measurements that indicate a 23-fold increase of the crystallite size to about 827 nm as a consequence of application of high temperature process. The controlled mechanochemical synthesis of Sb2S3 nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.Peer Reviewe

The influence of Al doping on microstructure and hyperfine interactions in FINEMET

Structure and hyperfine interactions of amorphous and nanocrystalline FINEMET were investigated by means of Mössbauer spectrometry. It was found that substitution of x iron atoms with aluminum ones causes changes in the properties of both amorphous and nanocrystalline alloys as well as in the structure of individual phases. The reduction of hyperfine magnetic field caused by atom substitution is a non-linear function of x, unlike the linear dependence expected because of dilution. Temperature studies reveal a double magnetic phase transition at 250°C and 330°C as well as point to the variety of phases in the examined material

Mechanochemical Dechlorination of PVC by Utilizing Eggshell Waste

Within this work, the dechlorination of polyvinylchloride (PVC) chemical as a model by co-milling with eggshell was performed in a planetary ball mill in order to show that mechanochemistry can be utilized for the simultaneous treatment of two wastes, while the products of the treatment can be used in further applications. The products of the reaction are water-soluble calcium chloride ($CaCl_2$), which can be used e.g. for de-icing of roads in winter and organic residue on the basis of ethylene, which can be recovered as energy source. The highest dechlorination yield (almost 97%) was achieved under following milling conditions: molar ratio between Ca and Cl: 2.34, ball-to-powder ratio: 65, rotation speed of the planet carrier: 550 rpm, milling time: 4 h and material of milling media: tungsten carbide. The optimum conditions were then applied for the removal of chlorine from industrial waste - the abandoned PVC window parapet. In this case, 95% dechlorination was evidenced