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

On the symmetry of magnetic structures in terms of the fibre bundles

The paper concerns the application of the fibre bundle approach to the description of the magnetic structures and their symmetry groups. Hence the explicit formulas describing both the variety of magnetic structures and their symmetry groups have been derived. The assumption was made that the bundle sections correspond to magnetizations of the separate crystal planes multiplied by a certain Gaussian factor defined in R3, the last factor making the problem continuous and more physical

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 temperature on critical fields in ZnxSbyCrzSe4

The electrical and complex ac dynamic magnetic susceptibility measurements were used to study an influence of temperature on critical fields in single-crystalline ZnxSbyCrzSe4 spinel system with y = 0:11, 0.16 and 0.20. The p-type conduction and a shift both of the Néel temperature TN to lower temperatures and a susceptibility peak at Tm in the paramagnetic region — to higher temperatures were established. Below TN the magnetic field dependence of susceptibility, Âac(H), shows two peaks. First peak at the critical field Hc1 slightly decreases with temperature and remains almost constant as Sb content increases. Second peak at the critical field Hc2 drops rapidly with temperature and remains almost unchanged as Sb content increases. At TN both critical fields disappear

Critical behaviour of the mean-field ferromagnet Cu1.02[Cr 1.77Ti0.24]Se4

Magnetization, M, and susceptibility, , measurements showed both strong lowering of magnetic moment in comparison with CuCr2Se4 matrix and zero- eld-cooling eld-cooling susceptibility splitting characteristic for the spin-glass behaviour. Isothermal magnetization curves, M(H), easy saturate and large values both of the Curie TC = 253 K and Curie Weiss = 283:5 K temperatures indicate the ferromagnetic order which coexists with the spin-glass state. The critical behaviour investigated around the paramagnetic ferromagnetic phase transition revealed that the values of critical exponents are close to those predicted by the mean eld model for long-range magnetic interactions

Mictomagnetic order in Cd0.87Cr1.93V 0.06Se4 semiconductor

The complex ac dynamic magnetic susceptibility was used to study the mictomagnetic-like behavior in polycrystalline Cd0:87Cr1:93V0:06Se4 spinel. The temperature dependences of the zero field in-phase (real part) and out-of-phase (imaginary part) components of fundamental susceptibility measured at the oscillating field Hac = 0:5 Oe and at the constant frequency of 125 Hz are characteristic for the mictomagnetic order. These results well correlate with the anomalies in the second and third harmonics of the ac susceptibility indicating the cluster glass

Electrical and magnetic studies of the CdxCryV zSe4 Spinels

The electrical and magnetic investigations carried out on the polycrystalline spinels with the general chemical formula CdxCryVzSe4 (where z = 0:06, 0.12, 0.24, and 0.31) revealed semiconducting and ferromagnetic properties with a Curie temperature of 127.5 K. A step-like structure of the electrical conductivity, ¾(T), was observed for the polycrystal containing 6% V ions in the octahedral sites while the remaining samples showed a typical Arrhenius behaviour of ¾(T). These effects are interpreted in terms of ferromagnetic spin clusters which finally dissolve on going towards the paramagnetic limit including non-stoichiometry

Spin crossover in CuxCoyCrzSe4 semiconductors

Magnetization and magnetic susceptibility measured in the zero-field-cooled mode were used to study the spin crossover transition in polycrystalline CuxCoyCrzSe4 compounds. With increasing Co content a transition from ferromagnetic order via ferrimagnetic one to antiferromagnetic-like behaviour was observed. This transition is accompanied with a lowering symmetry from cubic to monoclinic and for the latter the spin crossover phenomenon occurs. These results are considered in a framework of the ligand–field split and the spin–orbit coupling

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