Paramagnetism of Cu3RE2W4O18 semiconductors (RE = Gd, Dy-Er)

Cu3RE2W4O18 tungstates (RE = Gd, Dy Er) are paramagnets in the temperature range 4.2 300 K visible also in the absence of the energy losses in the curve of the imaginary part of magnetic susceptibility, 00. The negative values of the paramagnetic Curie Weiss temperature, , may suggest the weak antiferromagnetic coupling below 4.2 K. The temperature independent component of magnetic susceptibility has a positive value indicating a domination of the Van Vleck contribution. Calculations of the e ective number of the Bohr magnetons revealed that the orbital contribution to the magnetic moment comes mainly from the RE3+ ions

Molecular, spectroscopic, and magnetic properties of cobalt(II) complexes with heteroaromatic N(O)-donor ligands

New [Co(SCN)2(L)4/2] complexes, where L = b-pic (1), pyCH2OH (2), py(CH2)3OH (3), 1,2,4- triazolo[1,5-a]pyrimidine (4), [CoCl2(urotrop)2] (5), and [Co(DMIM)3]Cl2 H2O (6) where urotrop = hexamethylenetetramine and DMIM = 2,20-bis(4,5-dimethylimidazolyl) were synthesized in simple reactions of CoCl2 6H2O with ammonia thiocyanate and pyridine type ligands or urotropine and diimidazolyl ligands with cobalt(II) chloride in methanol solutions. The orthorhombic crystallization for (1), (2), and (4), the monoclinic one for (3) and (5) as well as the hexagonal one for (6) were found. The plots of the overlap population density-of-states indicated nonbonding character of the interactions between pyridine derivatives ligands and cobalt(II) ions in the complexes (1)–(4). The electronic spectra showed almost perfect octahedral complex in the case of (6). The magnetic susceptibility measurements revealed paramagnetic behavior with low values of the Curie–Weiss temperature, positive for complex (5) and negative for the other ones, although the transition to collective magnetic state at low temperatures for (4) and (5) was evidenced by an observation of antiferromagnetic coupling with Ne´el temperature of 4.5 K and the ferromagnetic one with Curie temperature of 10 K, respectively

Electrical transport properties of Yb8-xYxV2O17 (x = 0; 2; 8)

The UV-vis-NIR and electrical properties of Yb8xYxV2O17 for x = 0, 2, and 8 were investigated. The band energy gap of 2.6 eV determined for Yb6Y2V2O17 (x = 2) and comparable for the remaining compounds with x = 0 and 8 is characteristic for insulators. Low electrical conductivity with a characteristic minimum shifting to higher temperatures from 322, via 360 to 370 K in the sequence x = 0, 2 and 8, which decreases with increasing content of ytterbium was observed. Temperature dependence of thermoelectric power showed np transition at 410 and 467 K for x = 0 and 2, respectively, and n-type conductivity for x = 8, indicating mainly n-type electrical conductivity. A breakdown voltage of 26 V/mm is mainly observed for the IV characteristics at 400 K and showing a varistor-like behawior[…

Ferromagnetic order in single-crystalline (CdxAl y)[Cr2]Sez semiconductors

Measurements of the magnetic properties, the electrical conductivity and the Seebeck effect were performed on single crystals (CdxAly)[Cr2]Sez between 77 and 300 K. All samples have a ferromagnetic order with the Curie temperature of 130 K and the paramagnetic Curie–Weiss temperature of 155 K. Both these temperatures do not depend significantly on the Al substitution. The electrical conductivity of single crystals CdCr2Se4 doped with Al. was p-type and showed the change of log ¾ versus 1=T slope above 150 K. This fact is interpreted as being due to the onset of impurity conduction and structural defects

Superparamagnetic-like behaviour in RE2WO6 tungstates (where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er)

The magnetization isotherms were used to study the superparamagnetic-like behaviour in polycrystalline (powder) RE2WO6 tungstates (where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er). The magnetization isotherms of the majority tungstates under study revealed both the spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behaviour with blocking temperature TB ¼ 30 K except the Sm2WO6 and Eu2WO6 compounds

Electrical and magnetic characterization of ZnCr2-x V xSe4 spinel semiconductors

Single crystals of ZnCr2Se4 spinel doped with vanadium were prepared by chemical vapour transport. The chemical compositions of three crystals have been determined by X-ray diffraction. The structure refinement using the SHELXL-93 program system determine the cation distribution in the system as ZnCr2¡xVxSe4. For x values equal to 0.03, 0.1 and 0.13 the observed symmetry was cubic, space group Fd3m. Based on the structural data, influence of the V ions on the magnetic and electrical properties has been analyzed

Influence of Cr-substitution on the electrical properties of Fe1-xCrxVSbO6

Fe1xCrxVSbO6 solid solution is semiconductor with the activation energy decreasing both in the intrinsic and extrinsic conductivity temperature regions as the Cr-content increases. The n-type conduction is observed for Fe-richer samples while a change of the Seebeck coe cient (from n to p) for Cr-richer ones. Magnetic isotherms for all samples of solid solution under study are characteristic of the universal Brillouin function, indicating paramagnetic response. These e ects are discussed within the framework of the appearance of the mixed valence of both Fe and Cr ions

Hopkinson-like effect in single-crystalline CdCr 2Se 4 and Cd[Cr 1.89Ti 0.08]Se 4

The static (dc) and dynamic (ac) magnetic measurements of CdCr2Se4 and Cd[Cr1:89Ti0:08]Se4 showed their ferromagnetic properties with a Curie temperature TC 130 K and revealed on the real component of ac susceptibility curve, the peaks near TC at 200 Oe, 450 Oe and 1 kOe, characteristic for the Hopkinson ones. The meaningful reduction of saturation moment to 4.73 B/f.u. for Cd[Cr1:89Ti0:08]Se4 suggests the diamagnetic con guration of Ti ions, which dilutes the ferromagnetic sublattice of Cr ones and causes reducing of the energy losses visible on the imaginary components of ac susceptibility curve. Close for zero values of higher susceptibility harmonics above TC are pointing out to the lack of the spin uctuations in the paramagnetic state

Influence of Cr-substitution on the electrical properties of Fe1-xCrxSnSbO6

Fe1xCrxSnSbO6 solid solution shows semiconducting behaviour with the activation energy decreasing from EA = 0:64 eV for x = 0:0 to EA = 0:32 eV for x = 1:0 in the intrinsic conductivity temperature region as well as the n-type conduction at room temperature. The I–V characteristics and the conductance G at 300 and 400 K showed symmetrical and nonlinear behavior in the voltage range (–100, 100 V) suggesting the electron emission over the potential barrier especially for the boundary compounds FeSnSbO6 and CrSnSbO6. These effects are discussed in the context of the energy gap Eg > 1:6 eV many times greater than the thermal energy kT

High spin-low spin transitions in Cu 0.2Co 0.76Cr 1.83Se 4 semiconductor

Magnetization, ac and dc magnetic susceptibility measured in the zero- eld-cooled mode were used to study the high spin low spin transitions in polycrystalline Cu0:2Co0:76Cr1:83Se4 semiconductor. The real part component of fundamental susceptibility ′ 1(T) and its second ( 2) and third ( 3) harmonics revealed two spectacular peaks at 128 K and at 147 K, con rming the appearance of the spin-crossover phenomenon.Magnetization, ac and dc magnetic susceptibility measured in the zero- eld-cooled mode were used to study the high spin low spin transitions in polycrystalline Cu0:2Co0:76Cr1:83Se4 semiconductor. The real part component of fundamental susceptibility ′ 1(T) and its second ( 2) and third ( 3) harmonics revealed two spectacular peaks at 128 K and at 147 K, con rming the appearance of the spin-crossover phenomenon