12 research outputs found
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
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
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
Electrical and magnetic studies of ZnxMnyCr zSe4 p-type semiconductors
The structural, electrical and magnetic investigations carried out on the ZnxMnyCrzSe4 polycrystals with
y = 0:19, 0.29 and 0.38 revealed the spinel structure with the Mn ions occupying tetrahedral sites, p-type
conduction with polaronic transport at high temperatures and antiferromagnetic order with a Néel temperature
of 20 K and a Curie–Weiss temperature of 103 K. With increasing Mn content in a sample both the effective
magnetic moment and the re-entrant temperature increase while the first and second critical fields connected with
a metamagnetic transition and the breakdown of the conical spin arrangement decrease, respectively. These results
are interpreted in terms of giant cubic anisotropy as well as an effect of Mn impurities on the screw structure of
ZnCr2Se4
Effect of cation substitution on critical fields in the n-type Zn xSnyCrzSe4 spinel semiconductors
The ac dynamic magnetic susceptibility was used to study a cation substitution on critical fields in
polycrystalline (Zn0:87Sn0:048)Cr2:02Se4 and Zn0:93[Cr1:95Sn0:05]Se4 spinels with tetra- and octahedral coordination of Sn ions, respectively. An increasing static magnetic field shifts the Néel temperature TN to lower
temperatures while a susceptibility peak at Tm in the paramagnetic region — to higher temperatures. Below
TN the magnetic field dependence of susceptibility, Âac(H), shows two peaks at critical fields Hc1 and Hc2. The
values of Hc1 decrease slightly with temperature while the values of Hc2 decrease strongly with temperature,
especially for spinel with octahedral coordination of Sn ions, suggesting a weakness of the ferromagnetic component
Influence of Cu, Ga and Au dopants and technology conditions on the magnetic interactions in HgCr2Se4 single crystals
For single crystals HgCr2Se4 doped by nonmagnetic Cu+, Au2+ and Ga3+ ions and single crystals of
HgCr2Se4 matrix growing in different synthesis conditions both the dc and ac magnetic susceptibility as well as
the magnetization have been measured. As it follows from the analysis of the obtained results, paradoxically, the
dopants strengthen the long range magnetic interactions of the ferromagnetically ordered single crystals under
study, evidenced by the higher values of the ordering temperature in comparison with those ones for pure matrix.
An influence of the technological processes connected with deficiency and/or excess of Hg on the long range
magnetic interactions was not observed
Magnetic Compensation Effect in TbFe1-xAlxO3 System
Magnetic susceptibility measurements for solid solutions of TbFe1-xAlxO3, in the whole range of Al concentration, have been carried out. The obtained results indicate an essential role of the Al substitute in the magnetic behaviour of examined compounds. The generation of compensation effect, which modifies the susceptibility of the system, seems to be of particular interest. The compensation temperatures have been determined from some singularities visible on susceptibility cuves for compounds with Al concentration 0.03≤x≤0.70