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Polycrystalline samples of α-AgY1−xGdx(WO4)2 with x=0, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, and 1 have been prepared by a solid state reaction method and the influence of Gd3+ substitution for Y3+ on microstructure, thermal and magnetic properties was investigated. The X-ray diffraction analysis showed the phases to crystallize in the monoclinic symmetry, space group C2/m. A reversible monoclinic to tetragonal phase transition occurs in AgY1−xGdx(WO4)2 and strongly depends on Gd3+ ion concentration. Electron paramagnetic resonance (EPR) spectra of Gd3+ ions showed non-monotonous dependence of interaction strength on gadolinium concentration. Magnetic measurements showed paramagnetic behavior and strong increase of magnetic moment as the yttrium content decreases.

Broadband dielectric spectroscopy and magnetic measurements provide experimental evidence that the CdMoO4:Gd 3+ single crystal is the paramagnet with low relative dielectric permittivity (er � 8), which slightly depends on the temperature and frequencies. Magnetization with zero coercivity and remanence is almost a universal function of l0H/T, characterizing superparamagnetic-like behavior. These results are being considered in a framework of the random distribution of the Ga 3+ ions in the tetragonal structure.

The X-ray studies showed that the new CuCr2−xNixSe4 single crystals crystallized in the spinel structure with the space group Fd 3 ¯ m . Magnetic measurements revealed that both the long and short-range magnetic interactions are comparable and do not significantly depend on the Ni-content. Electrical measurements showed that p-type metallic conduction, thermopower and power factor decrease as the Ni-content increases. These results are considered in a framework of the structural defects, double exchange mechanism and mixed valence band of the chromium ions.

Electrical resistivity, thermoelectric power, broadband dielectric spectroscopy, magnetic susceptibility, and magnetization provide experimental evidence that the CdRE 2 W 2 O 10 tungstates (RE=Y, Nd, Sm, Gd–Er) are magnetically disordered insulators with low relative dielectric permittivity ( e r ∼15). These results are characteristic for paramagnetic insulators having the screened electrons on the filled shells. Some of them behave like superparamagnets with the blocking temperature of 30 K, depending on strength of the spin-orbit coupling.

Magnetic susceptibility measurements showed both a weak response to magnetic field and a lack of the Curie-Weiss region for CuEu2W2O10and Cu3Eu2W4O18tungstates characteristic for the multiplet widths comparable to thermal energy. Magnetization measurements displayed the linear temperature dependence with the lower magnetic moment for Cu3Eu2W4O18in comparison with CuEu2W2O10, indicating that the effect of the electric charges associated with the surrounding ligands can change the multiplet width of individual states. It is affecting the electrical properties of examined tungstates which reveal the insulating state and low relative permittivity εr ~ 29 in case of CuEu2W2O10and the thermally activated p-type electrical conduction for Cu3Eu2W4O18with the activation energy of 1.11 eV and the large value of εr ~ 217 above the room temperature.

Magnetic susceptibility measurements revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to the magnetic field and the temperature for Sm2W2O9 and Eu2W2O9 tungstates. The temperature independent component of magnetic susceptibility has a positive value for RE2W2O9 (RE = Pr, Nd and Gd) indicating a domination of van Vleck contribution. Only for Gd2W2O9 the magnetization is a universal function of µ0H/T, characteristic for the superparamagnetism.

In this work Sm 12.5 Co 66.5 Fe 8 Cu 13 ribbons, in the as-cast state and after annealing at 850 °C for 3 h, were studied. The investigated samples were obtained using the melt-spinning method. On the basis of X-ray diffraction patterns, it was found that sample in the as-cast state consisted of 0.88%, 14.47% and 84.65%, respectively of SmCo 5 , Sm 2 Co 17 and SmCo 7 phases. Annealing at 850 °C for 3 h resulted in decomposition of the metastable SmCo 7 phase into SmCo 5 and Sm 2 Co 17 . The magnetic measurements were performed using VSM, working in a magnetic field up to 2 T. From the hysteresis loops the magnetic parameters were determined. It was found that annealing process leads to deterioration of remanence from 0.60 T to 0.44 T and large increase in the coercivity from 1 kOe to 3.6 kOe. From the analysis of the recoil loops, it was found that the reversal magnetization process is complicated and mainly based on pinning of domain walls on grain boundaries.

The Zn 1− x Mn x Cr 2 Se 4 crystals were prepared by chemical vapor transport in closed silica tubes using ZnSe and MnSe with CrCl 3 as the transport agent. Four crystals with different Mn content ( x = 0.12, 0.13, 0.18 and 0.24) were studied by X-ray photoelectron spectroscopy (XPS) and magnetic measurements in order to determine influence of manganese on their magnetic and electronic properties. The XPS revealed no change of chemical shifts of Cr core lines indicating a Cr 3+ (3d 3 ) electronic configuration. Magnetization measurements revealed a systematic increase in saturation magnetic moments from 6.32 μ B /mol for x = 0.12 to 7.63 μ B /mol for x = 0.24, as well as effective paramagnetic Bohr magneton numbers from 4.87 μ B /mol for x = 0.12 to 6.91 μ B /mol for x = 0.24.

Selenospinels ACr 2 Se 4 form a broad class of materials with tunable properties, including thermoelectric, magnetoresistive and magnetocapacitance, related to the internal competing interactions. On the basis of structural, magnetic and numerical studies of the cubic ZnCr 2− x Ni x Se 4 ( x = 0.1–0.3), we show that simple ionic model is not suitable for consistent description of the properties of the system. Although it may explain the systematic decrease of the saturation magnetic moments from 5.25 μ B /f.u. for x = 0.1 to 4.85 μ B /f.u. for x = 0.3, it fails to explain the trends in the lattice parameters and the chemical shifts of the absorption edges. On the basis of the numerical calculations performed for x = 0.2, we obtain the agreement between the local magnetic moments on Cr (3.18 μ B ) and Ni (−0.49 μ B ) ions and the value obtained from neutron powder diffraction 2.65(3) μ B as well as saturation magnetization. However, the calculations and the consistence between different experiments require the presence of magnetic polarization on selenium −0.11 μ B , which is usually neglected in ionic models.

The crystal structure, X-ray photoelectron spectra (XPS), dc magnetic isotherm, ac magnetic susceptibility and specific heat measurements for antiferromagnetic and semiconducting ZnCr 2 Se 4 spinel diluted with Ga, In and Ce are presented. For all the studied spinels the XPS spectra exhibit the Cr 2 p 3/2 splitting of 1 eV characteristic for the 3 d 3 electron configuration of the chromium ions. A correlation between the second critical field H c2 of the helix to paramagnetic transition and the magnetic specific heat C -peak was found in (Zn 0.86 Ce 0.08 )[Cr 2 ]Se 4 . This correlation weakens for (Zn 0.99 )[Cr 1.92 Ga 0.06 ]Se 4 and disappears for (Zn 0.83 In 0.11 )[Cr 1.73 In 0.14 ]Se 4 as the saturation magnetic moment rapidly decreases in the sequence Ce, Ga and In. The magnetic contribution to the specific heat displays a sharp peak at T N and is maximal at the spin fluctuation temperature of 40 K, which is related to the maximum of the magnetic susceptibility at the same temperature and at 50 kOe in the spin fluctuation region, evidenced by the entropy exceeding 90% of the entropy calculated classically for the complete alignment of the Cr spins, S m = R ln(2 S + 1). These effects are considered within the cation–anion distances in octahedral sites, the cation deficiency and the spin state of 3 d Cr 3+ ions in t 2g orbital.

Magnetic susceptibility measurements carried out on (Co,Zn)RE4W3O16 compounds revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to magnetic field and temperature for ZnSm4W3O16 and ZnEu4W3O16 samples. The temperature independent component of magnetic susceptibility has a negative value for ZnGd4W3O16 and a positive one for the rest of the tungstates, indicating a domination of van Vleck contribution. The magnetization isotherms of majority of the tungstates under study revealed both spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behavior with blocking temperature TB∼30 K, except for ZnEu4W3O16. Fitting procedure of the Lande factor revealed that the stronger the orbital contribution, the weaker the superparamagnetic effect, namely for ZnRE4W3O16. In case of CoRE4W3O16 a significant participation of the Co2+ moment in the spontaneous magnetization was observed.

A high spin (HS) – low spin (LS) transition has been discovered in the Co[Cr0.5Ga1.5]S4 spinel, where the Co ions occupy tetrahedral sites and the Cr and Ga ions octahedral ones. The latter are diluted by the non-magnetic Ga-ions. Application of magnetic fields revealed ferrimagnetic order with a Curie temperature TC = 126 K, a strong suppression of the magnetic susceptibility () and a slight shift of TC to lower temperatures. A cusp at 15.6 K on the ac (T) curve suggests a spin frustration of the re-entrant type. Characteristic for the HS-LS transition is an inflection point at 150 K on the 1/(T) curve, a lack of the Curie-Weiss region above TC and a small value of the magnetization, 4.76 emu/g at 4.4 K and at a magnetic field of 57.5 kOe.

The Co2Sm2W3O14 compound crystallizes in the orthorhombic system, and melts congruently at 1443 K. The magnetic measurements showed that Co2Sm2W3O14 is a paramagnet in the temperature range 4.2-225 K showing both the residual magnetic interactions since the paramagnetic Curie-Weiss temperature   0 and the uncompensated temperature independent contributions of magnetic susceptibility since 0  0. The Brillouin fit of the Landé factor revealed an increase of the orbital contribution to the total magnetic moment of the compound what seems to be responsible for its hard and spontaneous magnetization at low temperatures.

The spinel stoichiometric compounds of the CuCr 2 − x Sb x Se 4 family were obtained for the first time and prepared with the assumption of the valence of Sb ions equal to 3. The magnetization isotherms at 4.2 K and at the magnetic stationary fields up to 14 T as well as the temperature dependencies of magnetic susceptibility were studied in the temperature range of 4.2 ÷ 400 K. These results were compared with analogous measurements performed earlier by the authors for the nonstoichiometric spinel family built of the same elements and obtained under the assumption of the valence of Sb ions equal to 5. From this comparison it follows that these two spinel series reveal significant differences: (1) The interval of possible concentrations of Sb ions in the obtained stoichiometric spinel samples under study is up to 1.0, whereas for the nonstoichiometric spinels is (0.30 ÷ 0.48). (2) The corresponding intervals for the appearance of the spin glass states are: (0.2 ÷ 1.0) and (0.30 ÷ 0.48), whereas the freezing temperatures do not differ significantly. (3) The magnetization processes in the stoichiometric samples depend strongly on the Sb concentration, whereas in the nonstoichiometric samples they run very hardly.

Magnetization and susceptibility were investigated as a function of temperature and magnetic field in polycrystalline Mn[Cr 0.5 Ga 1.5 ]S 4 spinel. The dc susceptibility measurements at 919 Oe showed a disordered ferrimagnetic behaviour with a Curie–Weiss temperature θ CW =−55 K and an effective magnetic moment of 5.96 μ B close to the spin-only value of 6.52 μ B for Cr 3+ and Mn 2+ ions in the 3 d 3 and 3 d 5 configurations, respectively. The magnetization measured at 100 Oe revealed the multiple magnetic transitions with a sharp maximum at the Neel temperature T N =3.9 K, a minimum at the Yafet-Kittel temperature T YK =5 K, a broad maximum at the freezing temperature T f =7.9 K, and an inflection point at the Curie temperature T C =48 K indicating a transition to paramagnetic phase. A large splitting between the zero-field-cooled (ZFC) and field-cooled (FC) magnetizations at a temperature smaller than T C suggests the presence of spin-glass-like behaviour. This behaviour is considered in a framework of competing interactions between the antiferromagnetic ordering of the A (Mn) sublattice and the ferromagnetic ordering of the B (Cr) sublattice.

Barium hexaferrite (BaFe12O19) powders of particle size of 130 and 180 nm were synthesized by a single microemulsion technique. The influence of the concentration of Ba2+ and Fe3+ metallic ions in the aqueous phase in the microemulsion system on the particle size distribution, crystallinity and magnetic properties of BaFe12O19 was studied. The coercive force and saturation magnetization of the sample obtained at a lower concentration of metallic cations in the aqueous phase were higher than those of the sample obtained at higher concentration.

The experimental evidence of metamagnetism, giant negative magnetoresistance and spin glass state is presented for the compounds under study. An attempt is made to explain the jump-like phase transition of the colossal negative magnetoresistance of −4433% at 153.2 K into the colossal positive magnetoresistance of +980% at 154.2 K for the spinel sample with selenium. It was emphasized that in all the phenomena described in this paper the double exchange magnetic interaction plays the main role.

In this article is pointed out the particularly important role of the double exchange magnetic interaction in the appearance of the phenomenon of the coexistence of the negative giant magnetoresistance and the spin glass state in the selected RE-manganites and the spinels with chromium. To explain this phenomenon, its statistical background and the types of magnetic interactions in the compounds under study are taken into account. The particular importance of the double exchange magnetic interaction “cooperating” with the strong external magnetic induction results here from that: i. its coupling constant is several times greater than the superexchange one, ii. the spin orientation of the hopping electrons is conserved (always ferromagnetic coupling!) and the charge transfer makes the p-type metallic conductance.

Single crystals of the spinel solid solutions ZnCr 2− x Al x Se 4 with x = 0.15 and 0.23 were grown and studied by X-ray diffraction and macroscopic magnetic measurements. The solubility of Al 3+ ions in the parent compound ZnCr 2 Se 4 is very limited and only weakly substituted single crystals can be obtained. The spinel structure is hardly modified by this admixture and regular cation distribution is preserved. Alike ZnCr 2 Se 4 , the two compounds investigated order antiferromagnetically at low temperatures. Both the Neel temperatures and the paramagnetic Curie temperatures are similar to that reported for the parent selenide. Also the effective magnetic moments are close to that of ZnCr 2 Se 4 and compatible with trivalent Cr ions. In contrast, the saturation magnetic moments measured above the metamagnetic phase transitions in strong magnetic fields and calculated per one Cr atom, appear to be strongly affected by the Al-substitution, being rapidly suppressed with rising Al-content.

Motto The first address of Satan to the human race began most modestly with the word: why? Adam Mickiewicz (1798–1855) The resistance, magnetoresistance and magnetization measurements have been performed in the temperature range of 4.2–300 K and in the external magnetic inductions up to 14 T for the Sm1− x Sr x MnO3 (x = 0.33, 0.45) and RE0.55Sr0.45MnO3 (RE0.55 = Eu0.397Nd0.153, Tb0.25Nd0.30) manganites. In these samples the metal–semiconductor phase transitions as well as two kinds of the magnetic phase transitions the ferromagnetic–paramagnetic and metamagnetic (both spin-flip and spin-flop) have been observed. It was found that correlations between the magnetic and electrical phase transitions appear at high values of the external magnetic inductions. These correlations consist, simultaneously, of the large negative magnetoresistance and metamagnetic phase transitions. The existence and reconstruction of the ferromagnetic and antiferromagnetic clusters under the influence of the external magnetic induc...

High degree of defectiveness both in the stoichiometric CuCr 2− x Sb x S 4 ( x = 0.3, 0.4, 0.5) and nonstoichiometric Cu 1 + x Cr 1.5 + y Sb 0.5 + z Se 4 + t (where: −0.02 ≤ x ≤ 0.01, 0.03 ≤ y ≤ 0.35, −0.2 ≤ z ≤ −0.02, 0.01 ≤ t ≤ 0.08) spinels doped with Sb has been determined with the aid of the vacancy model. From the analysis carried out of the effective magnetic moments and the exchange integrals, it follows that in the spinels with sulphur mainly the cation subarrays are defected whereas in the spinels with selenium the defectiveness appears mainly in the anion subarrays. It turned out that in the spinels with sulphur the ferromagnetic cluster spin glass states appear accompanied by the large negative magnetoresistance, whereas in the spinels with selenium the corresponding clusters are antiferromagnetic and the giant magnetoresistance has been observed both positive and negative. A jump-like phase transition was here observed changing both the sign and the measured value of the magnetoresistance from −4433% at 153.2 K up to +980% at 154.24 K. Moreover, in the spinels with selenium both semiconductor–metal and metal–semiconductor phase transitions have been observed from the temperature dependence of the resistance.

Mixed selenide spinels of (Cd)[Cr 1.81 In 0.19 ]Se 4 and (Cd 0.745 In 0.255 )[Cr 1.94 In 0.06 ]Se 4 have been studied using X-ray diffraction, magnetic measurements and ESR spectroscopy. In 3+ ions accommodate both tetrahedral and octahedral sites in the spinel structure. The magnetic short-range order appears in the critical region from T c to about 200 K for the selenide spinels. The linear temperature dependence of the resonance linewidth at T >250 K is interpreted by an occurrence of one-phonon process in a spin-lattice relaxation.

DyPdAl single crystals grown by the Czochralski method crystallized in the hexagonal ZrNiAl-type structure. The measurements of the lattice parameters, electrical resistivity and magnetic properties confirmed the absence of an iso-structural transition similar to HoPdAl and contrary to GdPdAl and TbPdAl. The effective magnetic moment agrees with the free ion value of Dy3+. Palladium does not contribute to density of states at the Fermi level. The dysprosium sublattice orders at 25 K. Below 17 K, a reorientation of the magnetic moment is observed.

Thermoelectric power and electrical resistivity as well as magnetic measurements carried out on Nb2VSbO10 showed a diamagnetic behavior, an insulating state up to 360 K and above this temperature n-type semiconducting properties with the activation energy of 0.55 eV. The I–V characteristics both at 300 and 400 K are symmetric and non-linear (back to back varistor-like). A computer-assisted curve fitting procedure of the conductance G vs. the applied voltage V showed the relation G ~ V3/4, which is interpreted in a framework of deep donor and shallow trap levels as well as grain boundaries.

Magnetic properties of Zn1-xMxCr2Se4 (M=In, Ni, Al, Ga) in high magnetic field up to 14 T and at low temperatures are presented. ZnCr2Se4 belongs to the group of normal spinels with Zn2+ located at tetrahedral (A) sites and Cr3+ occupying (B) sites of the cubic close-packed array of selenium anions. Magnetic order in the compounds is connected with superexchange interactions, which are positive between the nearest neighbors and negative between the next-nearest neighbors. Substitution of one of the cations of spinel with another 3d metal causes essential changes in the cation distribution and physical properties.

The single crystals of Cd x Ni y Cr z Se 4 ( x + y + z ≈ 3 ) were prepared by a chemical vapour transport in closed silica tubes using CdSe and NiSe with CrCl 3 as the transport agent. The chemical compositions of selected crystals have been determined by X-ray electron probe microanalyzer. The influence of the Ni substitution into the spinel structure of CdCr 2 Se 4 has been analyzed on the basis of the experimental data for the magnetization in the external magnetic fields. The nickel substitution did not cause an observable change in the saturation magnetic moments in the measured samples.

Powder samples of CuCr 2− x Sb x S 4 were obtained for x =0.3, 0.4 and 0.5. All the samples have spinel structure. The magnetization measurements were carried out with the use of the induction method in the temperature range of 4.2–300 K in stationary fields with inductions up to 14 T. Both the electrical conductivity and the magnetoresistivity were measured in the same range of temperatures with the use of the four-point method. For the magnetoresistivity measurements both stationary fields up to 14 T and pulsed fields of 38 T were applied. A lack of magnetic saturation is observed for all the samples. Moreover, an increase of the antiferromagnetic component of the magnetization is observed with the increase of the Sb concentration. The absolute values of magnetoresistivity as a function of x exhibit at 4.2 K and 14 T a maximum at about x =0.4, assuming zero at x =0.5. For the two concentrations, i.e. for x =0.3 and 0.5, the magnetoresistivity at room temperature changes its sign twice as a function of the magnetic field. A peak clearly seen in the temperature dependence of the relative derivatives of both the magnetization and susceptibility seems to testify to a spin-flip transition at 13 K and 1 T.

The temperature dependence of the lattice parameters, electrical resistivity, DC and AC magnetic susceptibility of GdRhAl, which crystallizes in a TiNiSi type structure, show no isostructural phase transition, contrary to GdPdAl crystallizing in a ZrNiAl type structure; the ordering temperature was 30 K. Below this temperature a weak reorientation of the magnetic moment was found in measurements of the magnetization in strong magnetic fields. The effective magnetic moment, slightly enhanced in comparison with the free ion value of Gd 3+ , was 8.06 μ B . ESR measurements reveal a small contribution of the Rh 4d electrons to the valence band and XPS measurements show a narrowing of the Rh 4d band in the compound in relation to pure Rh. The Rh 4d electrons preserve band character in the compound and the hybridization of the Gd 5d, Rh 4d and Al 3p electron states determines the magnetic properties.

Ho 3 Rh single crystal exhibits anisotropic properties. An ordering of holmium sublattice at 35 K and a spin reorientation process at 25 K in the magnetization, dc and ac magnetic susceptibility is observed. The electrical resistivity measurements confirm these phenomena. The temperature dependence of the lattice parameters and the unit cell volume show a magnetovolume effect below the ordering temperature. The XPS electronic structure measurements indicate hybridization of the rhodium 4d states and conduction band, which influences the properties of Ho 3 Rh.

A giant magnetoresistance (MR) is found in the CuCr 1.6 Sb 0.4 S 4 semiconductor spinel, consisting of a solid solution of the CuCr 1.5 Sb 0.5 S 4 antiferromagnet (AF) and the CuCr 2 S 4 ferromagnet. This MR is negative and isotropic. Its value is equal to 74% at temperature T = 3 K (magnetic field H = 38 T) and decreases with decreasing T. Magnetization isotherms are the superposition of a linear part, as for AF, and a small spontaneous magnetization. Therefore we assume that the sample is an AF in which droplets with spontaneous magnetization are disposed. Nagaev showed that giant MR in doped AF semiconductors is explained by similar magnetic two-phase state, in which all the electrons are concentrated in droplets because of the energy gain in s-d exchange.

Er 3 Ir single crystals were grown by the Czochralski method from a levitated melt. The electrical resistivity thermal dependence exhibits ordering temperature of the erbium sublattice at 40 K and a spin reorientation process at 22 K. The DC and AC magnetic susceptibility show antiferromagnetic ordering in the form of an asymmetric peak. The magnetization in strong magnetic fields up to 140 kOe exhibits anisotropy. The lattice parameters’ thermal dependence of Er 3 Ir and Er 3 Ni show anisotropy and anomalous behaviour.

Single crystals of ZnCr2Se4 spinel doped with nickel were prepared by chemical vapour transport in closed silica tubes using ZnSe and NiSe with CrCl3 as the transport agent. The chemical compositions of three crystals have been determined by X-ray diffraction for the system Zn–Ni–Cr–Se to determine the cation distribution and to study an influence of the Ni ions on the magnetic properties of the system. Based on the structural data the formula describing cation distribution in the system is: Zn[Cr2−xNix]Se4. For x values equal to 0.03, 0.05 and 0.10, the observed symmetry was cubic, space group Fd-3m. The site occupation factors resulting from the structure refinement showed Ni2+ substituted for the Cr3+ ions on octahedral sites. The experimental data for the saturation magnetization on the concentration of nickel in the external magnetic fields have been analyzed. The nickel substitution modified the saturation magnetic moments, which decrease with increasing Ni concentration (comparatively to the parent ZnCr2Se4).

Single crystals of the intermetallic ternary compound GdPdAl, crystallizing in the hexagonal ZrNiAl-type structure, were grown by the Czochralski method. Lattice parameters, electrical resistivity, magnetic susceptibility give evidence of an isostructural phase transition from a high temperature modification HTM I phase to HTM II phase at 180 K. The jump related to this transition causes a decrease of the lattice parameter a of 0.7% and an increase of the lattice parameter c of 1.3% during the cooling process. These changes are responsible for some microcracks in the single crystal. Besides the structural phase transition, magnetic ordering of the Gd sublattice is observed at 48 K. At about 20 K a spin reorientation process may occur. The XPS measurements of GdPdAl reveal a dominating contribution of d electrons at the Fermi level. For comparison the electronic structure of TbPdAl was also examined. Both compounds reveal formation of a narrow Pd 4d band. Further information on changes of the electronic structure at the isostructural phase transition were obtained from the temperature dependence of the ESR linewidth.

CuCr 1.6 Sb 0.4 S 4 crystallizes in the spinel structure with the lattice parameter a =9.9680(1) A and the anion parameter u =0.3820(1). The very hard magnetization of the sample, the shape of the magnetization isotherms as well as the lack of magnetic saturation even in a field of B =14 T indicate that the antiferromagnetic superexchange interaction dominates the long-range magnetic interactions between the magnetic moments localized on the chromium ions. A high positive value of the paramagnetic Curie–Weiss temperature Θ C–W (equal to 318 K) testifies that the short-range interaction is ferromagnetic and strong which means that in the corresponding microregions the double exchange interaction is present and predominates. A suggestion is made that these microregions behave like superparamagnetic clusters. As the result of the competition of the interactions mentioned above the sample under study reveals a spin glass state at low temperatures, which is confirmed by the temperature dependence of the magnetic susceptibility curves. The spin-freezing temperature is lower than 50 K. CuCr 1.6 Sb 0.4 S 4 is a semiconductor with a giant negative magnetoresistivity equal to 74% at 38 T and 3 K. The driving force of this effect is the double exchange magnetic interaction. Three values for the activation energy were observed: E 1 =0.118 eV, E 2 =0.004 eV and E 3 =0.033 eV. These are most probably connected with the energy levels generated by the crystal field.

Single crystals of the HoMn 2 compound were grown by the Czochralski method from a levitated melt. The thermal dependence of the electrical resistivity exhibits a magnetic transition at 29 K. A second transition occurs at 21 K. Moreover, for ρ ( T ) a T 2 dependence at low temperatures and saturation effects above 250 K were found. The magnetization in strong magnetic fields and the DC and AC magnetic susceptibilities measured along the principal crystallographic directions show ordering of the holmium moments to a spin-canted magnetic structure at about 25 K and a spin reorientation below 21 K.

A giant magnetoresistance, reaching 74% in a magnetic field of 38 T at 3 K, was observed in the CuCr1.6Sb0.4S4 semiconductor spinel. The magnetic properties point to the existence of a magnetic two-phase state in this compound. The giant magnetoresistance was explained by the existence of the magnetic two-phase state due to strong s-d exchange.

Single crystals of the DyMn 2 compound were grown by the Czochralski method from a levitated melt. The electrical resistivity exhibits a magnetic transition at 40 K, a second transition at 25 K, a cubic temperature dependence at low temperatures and a saturation effect above 250 K. The magnetization in strong magnetic fields, and the DC and AC magnetic susceptibility measured along the principal crystallographic directions show an ordering of the dysprosium moments to a spin-canted magnetic structure at about 40 K and a spin reorientation below 25 K. The temperature dependence of the lattice parameter shows a lattice contraction below 40 K.

Single phase GdCoAl, GdCuAl and single crystal GdNiAl samples of good quality were synthesized. The electrical resistivity, magnetization and AC susceptibility as a function of temperature revealed in all these compounds a ferromagnetic ordering at 100, 83 and 60 K, respectively. A magnetic transition, probably to a non-colinear structure was observed in GdNiAl at 31 K as well as the presence of the third magnetic transition at 14 K, while in the GdCuAl compound an evidence of similar transition was found at 23 K. In GdNiAl a transition between two different crystallographic phases of ZrNiAl-type was observed at 220 K. The transition was accompanied by rapid jumps of crystal lattice parameters and of the electrical resistivity. The structure determined above and below the transition point showed significant changes of the Gd–Gd and Gd–Ni interatomic distances. The observed phase transition was attributed to the filling of the Brillouin zone by the electrons at the Fermi level and to the rearrangement of the interatomic bond lengths, resulting in new density of states distribution and a lower density of states at the Fermi level. This assumption is consistent with the observed change of the relaxation rate between Gd 4f moments and the conduction electron system. The XPS investigation revealed the essential role played by the 3d electrons of the transition metals in these compounds. As a consequence, different contributions of d states to the valence band affect the structural, magnetic and transport properties of these compounds.

The magnetic properties of the solid solutions of MoO 3 in SbVO 5 for 5, 10 and 15 mol% were investigated by the magnetic susceptibility χ σ ( T ) and magnetization σ ( B ). With increasing MoO 3 in SbVO 5 from 5 to 10 mol% the antiferromagnetic order shifts to higher temperatures and a Neel temperature of T N ≈ 6 K accompanied with a negative increase of the Curie–Weiss temperature from θ CW ≈ −6 K to −58 K is observed, indicating a change in the magnetic structure from non-collinear of the Yafet–Kittel type to a collinear antiferromagnetism. For 15 mol% a conical magnetic spin arrangement is likely. The values of the electrical resistivity ρ ( T ) and of the thermopower S at high temperatures indicate that all solid solutions are thermally activated p -type semiconductors above 325 K.

Magnetic properties of the spinel single crystals with the general chemical formula CuxInyCrzSe4 (where y = 0.074, 0.1, 0.12, 0.15, 0.16, 0.48, 0.54 and 1.14) have been studied. Ferromagnetic ordering with a Curie temperature of 330 K up to y = 0.16, spin glass-like behavior with freezing temperature of 36 K for y = 0.48 and the antiferromagnetic ordering with Neel temperature of 21 K for y = 0.54 were established. The results above mentioned are related to the exchange integrals, suggesting that with increasing indium ions with tetrahedral coordination a local competition of both superexchange ferromagnetic and antiferromagnetic interactions undergoes a complex order–disorder–order transition with the reversal spin.

High resolution XPS measurements of the Gd3Pd valence band and core level states reveal formation of a narrow Pd 4d band. The Pd M45N45N45 Auger spectrum of Gd3Pd exhibits narrow, quasiatomic spectral features in comparison with the bandlike character observed for pure Pd. The effective Coulomb interaction Ueff between two 4d holes on the same atomic site was determined. The complex character of the valence band influences the magnetic properties of the compound.

Er 3 Rh single crystals were obtained by the Czochralski method from a levitated melt. The electronic structure, lattice parameters, magnetization in strong fields, AC and DC magnetic susceptibility and electrical resistivity were measured along the principal crystallographic directions. A highly anisotropic behavior for the magnetization and lattice parameter was observed. An antiferromagnetic transition at T N =26 K was found.

From X-ray microprobe analysis the formula Cu x Zn y Cr z Se 4 ( x + y + z ≈3) for the investigated single crystals was determined. The experimental data for the magnetization and the magnetic susceptibility, as well as their dependence on temperature and on the concentration of zinc in the external magnetic fields have been analyzed. The saturation moments for small zinc content are closer to CuCr 2 Se 4 . For higher zinc contents the magnetic moment increases to values closer to noncuprate spinels.

Although the compounds CdCr2S4 and CuCr2S4 are ferromagnetic, solid solutions of the system CdCr2S4-CuCr2S4 with the spinel normal structure show a ferrimagnetic ordering of their magnetic moments with Curie temperatures of about 90 K. For all the samples under investigation one can observe a significant lowering of the saturation magnetic moment in comparison with the theoretical one. Moreover, metamagnetic thresholds were observed at different temperatures. In particular at 250 K the values of the induction of the magnetic field for these thresholds are equal to 0.1 T for x = 0.05, 0.4 T for x = 0.1, 1.1 T for x = 0.15 and 0.4 T for x = 0.2, respectively. The lowering of the saturation magnetic moment and the existence of the metamagnetic thresholds for all the samples under study seem to be connected both with the high defectiveness of the crystal structure and with the mixed valence of the chromium ions. An attempt is made to interpret this fact in terms of the RKKY, double-exchange and superexchange magnetic interactions as well as with the use of the vacancy parameter.

The experimental data for the magnetization and the magnetic susceptibility, as well as their dependence on temperature, on the induction of the external magnetic field and on the concentration x have been analyzed. The metamagnetic phase transitions induced by the external magnetic field have been observed as plateau areas and jump-like increments on the magnetization curves at 4.2 K. High values of the effective magnetic moment μ eff and of the Curie constant C M point to the existence of Cr 2+ ions as well as Cr 3+ ions. The exchange constants, transfer integrals and the spiral angles for the solid solutions under study have been evaluated.

Magnetization measurements of Dy 3 Ni single crystal were performed in static magnetic fields up to 140 kOe and impulsed fields up to 400 kOe along the principal crystallographic directions. For all measured directions the metamagnetic transitions with hysteresis loops were found below T N .

All the compounds under study show the spinel normal structure. The lattice parameters decrease with an increase in the Cu concentration. The samples with low Cu concentrations ( x ≤ 0.2) exhibit ferrimagnetic ordering and Curie temperatures of 150 K. The samples with high Cu concentrations ( x ≥ 0.9) are ordered ferromagnetically, and their Curie temperatures are much higher and close to 480 K. Moreover, for the four samples under investigation one can observe a significant lowering of the saturation magnetic moment in comparison with the theoretical one. This lowering seems to be connected with the high degree of defects in the crystal structure. An attempt is made to interpret this fact with the use of the vacancy parameter.

In the spinels under study the spin glass state was observed at x =0.3, 0.4. The spin-freezing temperature is equal to about 47.4 and 30 K for x =0.3 and 0.4, respectively. The temperature range, in which the spin glass state appears, is much narrower for x =0.3 than for x =0.4. The negative magnetoresistance decreases significantly with the decrease of Sb concentration.

Single crystals of the HoMn 2 compound were grown by the Czochralski method from a levitated melt. The thermal dependence of the electrical resistivity exhibits a magnetic transition at 29 K. A second transition occurs at 21 K. Moreover, for ρ ( T ) a T 2 dependence at low temperatures and saturation effects above 250 K were found. The magnetization in strong magnetic fields and the DC and AC magnetic susceptibilities measured along the principal crystallographic directions show ordering of the holmium moments to a spin-canted magnetic structure at about 25 K and a spin reorientation below 21 K.