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The II-VI compound semiconductor cadmium zinc telluride (CZT) is very useful for room temperature radiation detection applications. In the present research, we have successfully grown Bi doped CZT single crystals with two different zinc concentrations (8 and 14 at. %) by the Bridgman oscillation method, in which one experiment has been carried out with a platinum (Pt) tube as the ampoule support. Pt also acts as a cold finger and reduces the growth velocity and enhances crystalline perfection. The grown single crystals have been studied with different analysis methods. The stoichiometry was confirmed by energy dispersive by x-ray and inductively coupled plasma mass spectroscopy analyses and it was found there is no incorporation of impurities in the grown crystal. The presence of Cd and Te vacancies was determined by cathodoluminescence studies. Electrical properties were assessed by I-V analysis and indicated higher resistive value (8.53 x 108 Ω cm) for the crystal grown with higher zinc concentration (with Cd excess) compare to the other (3.71 x 105 Ω cm) [ABSTRACT FROM AUTHOR]

The production of surfactant-assisted metallic nanoparticles of TbCu has been achieved by the combination of high-energy ball milling in tungsten carbide containers and the use of oleic acid (CHO) and heptane (CH). The alloys were first produced in bulk pellets by arc melting and subsequently milled for only 2 and 5 h in oleic acid (15 and 30% mass weight). The powders consist of an ensemble of nanoparticles with a TbCu lattice cell volume of ≈215 Å, an average particle diameter between 9 and 12 nm and inhomogeneous lattice strain of 0.2-0.4%, as deduced from X-ray diffraction data. The nanometric sizes of the crystals with defined lattice planes are close to those obtained by transmission electron microscopy. Raman spectroscopy shows the existence of inelastic peaks between 1000 and 1650 cm, a characteristic of CHO. The magnetisation shows a peak at the antiferromagnetic-paramagnetic transition with Néel temperatures around 48 K (below that of bulk alloy) and a distinctive metamagnetic transition at 5 K up to 40 K. The Curie-Weiss behaviour above the transition reveals effective Bohr magneton numbers (≈9.1-9.9 μ) which are close to what is expected for the free Tb ion using Hund's rules. The metamagnetic transition is slightly augmented with respect to the bulk value, reaching H = 24.5 kOe by the combined effect of the size reduction and the lattice strain increase and the increase of magnetic disorder. At low temperatures, there is irreversibility as a result of the existing magnetic disorder. The moment relaxation follows an Arrhenius model with uncompensated Tb moments, with activation energies between 295 and 326 K and pre-exponential factors between 10 and 10 s. The results are interpreted as a consequence of the existence of a diamagnetic surfactant which drastically decreases the magnetic coupling between interparticle moments. [ABSTRACT FROM AUTHOR]

Herein we report on synthetic iron-intercalated vermiculites prepared from a Mg-vermiculite mineral from Santa Olalla, Huelva, Spain, by means of an ion exchange process from aqueous solutions of FeCl and FeCl. Thermogravimetric, X-ray diffraction, magnetic susceptibility and Mössbauer spectral studies have been used to characterize the synthetic iron-intercalated vermiculites. The results suggest that the intercalation process employed induces modifications in both the interlayer spacing and in the octahedral sheet; the disordered structure of the Mg-vermiculite mineral is not altered. The presence of solvated Fe(HO) ions has been shown by the Mössbauer spectroscopy. No magnetic order has been observed between 2 and 300 K neither in the Mg-vermiculite mineral nor in the two synthetic iron-intercalated vermiculites. [ABSTRACT FROM AUTHOR]

A series of GdCu 2 nanoparticles with controlled sizes ranging from 7 nm to 40 nm has been produced via high-energy inert-gas ball milling. Rietveld refinements on the X-ray diffraction measurements ensure that the bulk crystalline I m m a structure is retained within the nanoparticles, thanks to the employed low milling times ranging from t = 0.5 to t = 5 h. The analysis of the magnetic measurements shows a crossover from Superantiferromagnetism (SAF) to a Super Spin Glass state as the size decreases at NP size of 〈 D 〉 ≈ 18 nm. The microstrain contribution, which is always kept below 1%, together with the increasing surface-to-core ratio of the magnetic moments, trigger the magnetic disorder. Additionally, an extra contribution to the magnetic disorder is revealed within the SAF state, as the oscillating RKKY indirect exchange achieves to couple with the aforementioned contribution that emerges from the size reduction. The combination of both sources of disorder leads to a maximised frustration for 〈 D 〉 ≈ 25 nm sized NPs. [ABSTRACT FROM AUTHOR]

Highlights • Size reduction effects on the properties of a ferromagnetic Yb alloy are investigated. • A magnetic phase appears with mixed features of ferromagnetic and spin-glass systems. • Low temperature behaviors characteristic of disordered magnetic systems. Abstract We report changes on the magnetic behavior of the Heavy-Fermion ferromagnetic YbNi 2 alloy when reducing the size of the particles to the nanometer scale by high-energy ball milling. The milling process induces a reduction on the particle size of the bulk alloy down to 10 (2) nm and a lattice strain of 1.8 (2)%, for 30 h of milling time, as calculated from the X-ray diffraction data. The ferromagnetic transition at T C = 10.5 K in the bulk alloy tends to disappear whereas other magnetic transitions arise at lower temperatures with the milling process. The AC magnetic susceptibility of the 30 h milled sample shows a frequency independent peak at 3 K, in a wide range of frequencies, consistent neither with superparamagnetic nor simple freezing of the magnetic moments, and as expected for a ferromagnetic behavior. However, from the specific heat measurements in the 30 h milled sample, a peak at 3.6 K is shifted respect to that observed in the AC magnetic susceptibility, as found in spin glasses. Additionally, the specific heat on nanometric samples show reduced magnetic contributions respect to the bulk alloy with Δ c max around 0.45 J/molK. The results are explained by the influence of magnetic inhomogeneities and disorder of the alloys enhanced by the milling process in the ensemble of nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: The Co2−x Cu x (OH)AsO4 (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2)Å, b=8.559(2)Å, c=6.039(1)Å and a=8.316(1)Å, b=8.523(2)Å, c=6.047(1)Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O5-trigonal bipyramid dimers and M(2)O6-octahedral chains (M=Co and Cu) are present. Co2(OH)AsO4 shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21K within the presence of a ferromagnetic component below the ordering temperature. When Co2+ is partially substituted by Cu2+ions, Co1.7Cu0.3(OH)AsO4, the ferromagnetic component observed in Co2(OH)AsO4 disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx 2−y 2 orbital and the absence of overlap between neighbour ions. [Copyright &y& Elsevier]