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Thermo-EMF, magnetothermo-EMF, magnetoresistance, and magnetization of single-crystal samples of Nd(1–x)Sr x MnO3 and Sm(1–x)Sr x MnO3 with 0 ≤ x ≤ 0.3 have been studied experimentally. A sharp increase in the thermo-EMF and giant magnetothermo-EMF and magnetoresistance has been observed near the Curie point T C in compounds with 0.15 ≤ x ≤ 0.3. At the same time, no peculiarities have been found in compositions with x = 0. Since compounds with x > 0 consist of ferromagnetic clusters of the ferron type that reside in an antiferromagnetic A-type matrix, this means that the sharp increase in the thermo-EMF near T C is caused by ferrons. Indeed, the disappearance of ferrons due to a magnetic field or heating above T C leads to an abrupt decrease in the thermo-EMF. Therefore, thermo-EMF in alloyed magnetic semiconductors has been determined by the impurity concentration and the sample volume.

Thermopower, magnetothermopower, resistivity, magnetoresistance, and magnetization of singlecrystalline samples of the Sm1–xSrxMnO3 system (x = 0.15, 0.2, 0.25, 0.3) have been experimentally studied. These compositions consist of ferromagnetic clusters of the ferron type dispersed in the A-type antiferromagnetic matrix. Colossal thermo- and negative magnetothermopower values reaching 94.5% in a composition with x = 0.3 in the region of Curie point TC in a magnetic field of 1.323 T. This result implies that thermopower is mostly related to ferron-type clusters, since their breakage under the action of magnetic field or heating above TC leads to a sharp decrease in thermopower values. These results imply that thermopower in doped manganite semiconductors is determined by the concentration of impurity and volume of a sample.

The thermopower, S, magnetothermopower, ΔS/S, resistivity, ρ, and magnetoresistivity, Δρ/ρ, depending on the temperature T and magnetic field H, have been studied in an Nd0.5Sr0.5MnO3 single crystal consisting of three types of clusters: an antiferromagnetic CE-type with charge-orbital ordering (below the Neel temperature TNCE ~ 145 K) and an A-type with TNA ~ 220 K; a ferromagnetic at 234 ≤ T ≤ 252 K, and a ferromagnetic metal phase below the Curie temperature TC = 248 K. The thermopower was found to be negative, indicating the dominance of the electronic type of conductivity. In the S(T) curves, a sharp minimum is observed in the temperature range of 100 K ≤ T ≤ 133 K, close to TNCE, where the absolute S value attains 53 μV/K. With a further increase in temperature, the absolute S value decreases rapidly; at 200 K it is equal to 7 μV/K. It then slightly increases, reaching its maximum value of 15 μV/K at a temperature of 254 K, which is close to TC. The absolute thermopower decreased under the influence of the magnetic field; i.e., a negative magnetothermopower occurs. In {ΔS/S}(T) curves, a sharp minimum is observed at T = 130 K close to TNCE, where the magnetothermopower reaches a huge value of ~45% at H = 13.23 kOe. A broad minimum in the {ΔS/S}(T) curves is observed near the Curie temperature and its value is also high, viz., ~15% in the maximum measuring magnetic field of 13.23 kOe. The extremely high magnetothermopower values mean that the charge-orbital ordered nanoclusters or ferron type make the main contribution to the thermopower of the entire sample. The behavior of the ρ(T) and {Δρ/ρ}(T) curves is similar to that of the S(T) and {ΔS/S}(T) dependencies, which is in agreement with this conclusion.

Thermopower α and magnetothermopower ∆α/α were studied in the Sm0.55Sr0.45MnO3 samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature TC = 126 K, A-type antiferromagnetic clusters with the Neel temperature TNA ≥ TC and CE-type antiferromagnetic clusters with the TNCE = 240 K. The curves of temperature dependence of α (T) have a large maximum including TC and TNCE and the sharp minimum on the {∆α/α}(T) curves in the TC-region. Negative magnetothermopower in minimum achieves the giant value ~ 85% in magnetic field 14.17 kOe. It is shown that thermopower is largely caused by the presence of ferromagnetic nanoclusters of ferron-type and to a lesser degree of CE-type antiferromagnetic clusters, in which there is a charge ordering, displacing oxygen ions.

The thermopower α and magnetothermopower Δα/α have been studied on single-crystal Sm0.55Sr0.45MnO3 samples consisting of three types of magnetic clusters (ferromagnetic clusters with the Curie temperature TC = 134 K, the A-type antiferromagnetic clusters with the Neel temperature TNA ≥ TC, and the CE-type antiferromagnetic clusters with TNCE = 240 K). The temperature dependences of α and Δα/α have extremes in the vicinity of TNCE, namely, a wide maximum in curve α(T) and a sharp minimum in curve{Δα/α}(T). The negative magnetothermopower in the minimum has a giant value of 50% in the magnetic field of 13.2 kOe. The thermopower is shown to be mainly due to the existence of the CE-type antiferromagnetic clusters, in which there is a charge-orbital ordering that displaces the oxygen atoms. The changed crystal lattice inside these clusters changes the value of the thermopower inside them. This thermopower influences the voltage drop across the sample during measuring the thermopower and, thus, the effective value of α of the whole sample. The application of a magnetic field near TNCE accelerating the destruction of the CE-type antiferromagnetic order causes the sharp decrease in the thermopower of the whole sample. This implies that the CE-type antiferromagnetic clusters with the charge-orbital ordering make main contribution to the thermopower of the whole sample.

Thermopower α and magnetothermopower α/α were studied in the single-crystal Sm0.55Sr0.45MnO3 samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature TC = 134 K, A-type antiferromagnetic clusters with the Neel temperature TNATC and CE-type antiferromagnetic clusters with the TNCE = 240 K. The curves of temperature dependence of α (T) and {α/α}(T) have extrema in the TNCE-region: large maximum on the first and sharp minimum on the second. Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field 13,2 kOe. It is shown that thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order, displacing oxygen ions

Spontaneous generation of the electrical voltage in a Pr0.6Ca0.4MnO3 single crystal has been found. The charge and orbital ordering in the crystal takes place at T CO = 240 K, while the antiferromagnetic ordering occurs at T N = 174 K. As the temperature lowers, spontaneous voltage U increases initially slowly (in the temperature range from 300 K to T CO) and then more rapidly (in the range T CO-T N ). Starting from T N , the voltage U increases exponentially and, at 85 K, reaches 115 mV (in the ab plane) and 6.5 mV (along the c axis). The magnetic field differently affects the voltage U in different temperature ranges: it decreases the value of U in the temperature range of 85–130 K and increases in the range of 130–240 K. It is assumed that the spontaneous voltage is associated with the existence of ferromagnetic and charge orbital ordered clusters of different topologies in the crystal.

Spontaneous generation of electrical voltage U was found for the perovskite-like single crystal of Pr0.6Ca0.4MnO3, wherein the charge and orbital orderings occur at TCO = 240 K and the antiferromagnetic one occurs at the Neel point TN = 174 K. With decreasing the temperature, the U value increases first slowly (in the temperature range of 300 K-TCO) and then more rapidly (TCO-TN). Starting from TN, U increases exponentially and, at 85 K, reaches the value of 115 mV (in the ab plane) and 6.5 mV (along the c axis). The magnetic field has a different effect on the U value in different temperature ranges: in the temperature range of 85–130 K, it decreases U and, in the range of 130–240 K, increases U. The spontaneous voltage is thought to be caused by the existence of ferromagnetic and charge-orbital-ordered clusters of different topology in the sample. The latter clusters have own features and their structure are described by the non-centrosymmetric space group P21nm.

The magnetocaloric effect (MCE) in La1 − xSrxMnO3, Sm0.55Sr0.45MnO3, and PrBaMn2O6 compounds is studied. The maximum values of MCE (ΔTmax) determined by a direct method in the second and third compositions and in La0.9Sr0.1MnO3 are found to be much lower than those calculated from the change of the magnetic part of entropy in the Curie temperature (TC) and the Neel temperature (TN) range. The negative contribution of the antiferromagnetic (AFM) part of a sample in the La1 − xSrxMnO3 system at 0.1 ≤ x ≤ 0.3 decreases ΔTmax and changes the ΔT(T) curve shape, shifting its maximum 20–40 K above TC. Lower values of ΔTmax are detected in the range TC = 130−142 K in polycrystalline and single-crystal Sm0.55Sr0.45MnO3 samples cooled in air. If such samples were cooled in an oxygen atmosphere (which restores broken Mn-O-Mn bonds and, thus, increases the volume of CE-type AFM clusters), the maximum in the temperature dependence of MCE is located at TN (243 K) for CE-type AFM clusters. A magnetic field applied to a sample during the MCE measurements transforms these clusters into a ferromagnetic (FM) state, and both types of clusters decompose at T = TN. The PrBaMn2O6 composition undergoes an AFM-FM transition at 231 K, and the temperature dependence of its MCE has a sharp minimum at T = 234 K, where MCE is negative, and a broad maximum covering TC. The absolute values of MCE at both extrema are several times lower than those calculated from the change in the magnetic entropy. These phenomena are explained by the presence of a magnetically heterogeneous FM-AFM state in these manganites.

In Sm0.55Sr0.45MnO3single crystals, grown by the floating-zone method with the cooling in oxygen, has been observed the spontaneous generation of voltage (SGV). Its maximum reaches 60 μV and occurs in the temperature range where simultaneous decay of the CE-type antiferromagnetic order and the charge order take place in some clusters. The SGV peak becomes lower by about 45% if magnetic field 14.2 kOe applied. Also we observed the SGV in La0.75Ba0.25MnO3single crystals. Maximum value of SGV occurs in a vicinity of the Curie temperature. The SGV value seems to be almost independent from the cooling or heating rate and crystallographic direction, but in La0.75Ba0.25MnO3it is smaller than in Sm0.55Sr0.45MnO3by an order of magnitude. La0.75Ba0.25MnO3compound contains ferromagnetic clusters, in which the electrical charges are localized according to gain in thes-dexchange energy. They are distributed in the paramagnetic lattice, impoverished of an electrical charge. It is shown that SGV stems from the presence of regions with different electrical charges in both samples.

The magnetocaloric effect ΔT has been studied by a direct method in two samples of the manganite Sm0.55Sr0.45MnO3, namely, a single crystal (sample A) and a ceramic sample (sample C). The temperature dependences of the ΔT effect of both samples exhibit a maximum at T max = 143.3 K for the sample A and T max = 143 K for the sample C. In these maxima, the values of the ΔT effect are 0.8 and 0.4 K in the magnetic field H = 14.2 kOe for the samples A and C, respectively. In addition, the ΔT(T) curve of the sample A has a minimum at T min = 120 K, in which ΔT = −0.1 K. The maximum value of the ΔT effect increases with an increase in the magnetic field H in the range of magnetic fields up to 14.2 kOe, and the rate of this increase at H > 8 kOe is higher than that at H < 8 kOe. These features of the ΔT effect are explained by the presence of ferromagnetic and antiferromagnetic A- and CE-type clusters in the samples.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behavior of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behavior. For T  15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4-th period. These trends were explained by distinction of degree of division of the d (f)- or р-orbitals of neighboring atoms in the crystal. We calculated also the radii of the external d (f)- and р-orbitals and the nearest to them orbitals with the Slater’s method. It is demonstrated that in the superconducting crystals the d-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals.

A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster moment μc in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained by the competition between the carrier-mediated exchange and superexchange interactions.

Bulk and film samples of manganese-doped zinc-silicon diarsenide are obtained. Investigation of electrical and magnetic properties of ZnSiAs2: Mn samples showed that they possess the combination of ferromagnetic and semiconductor properties at above room temperature and are of interest as materials for spin transport.

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.

Basic tendencies in the distribution of ferromagnetic (FM), antiferromagnetic (AFM) and superconductive (SC) elements in the periodic table D.I. Mendeleev are traced. FM is observed at the elements in which 3d-shell is more than half-filled (the number of 3d-electrons 6 ⩽ n ⩽ 8 ), and at the elements with 4f-shell, contained k electrons in 4f-shell, at which the sum k + n ⩾ 8 . Estimation of the radii of the d-, f- and p-orbitals on Slater method shown that 3d- and 4f-shells of FM are more pressing, than the ones with smaller n and k + n , and are well separated in crystal. AFM is observed at the elements, at which 3d- or 4f-shells are precisely half-filled. SC is observed in the 3d-, 4d- and 5d-elements at 1 ⩽ n ⩽ x , x grows from 3 in 3d-elements to 7 in 4d- and 5d-elements, and in 7th period only at n = 2 and k + n = 3 . Further, SC is observed at the elements, at which 3p-, 4p-, 5p- and 6p-shells contain no more than 4 electrons. In SC crystals the wave functions of external d- and p-electrons of each atom penetrate inside neighbor atoms and overlap with corresponding wave functions with smaller main quantum number than of central atom. In this case the separation of spin and charge in electron is quite possible and the charges without spin become bosons. Spins obtained magnetic moments are ordered antiparallel by two. At transfer that pair in the parallel state by magnetic field its magnetic flux from magnetic field component along of magnetic field is equal to 1 fluxon (quant of magnetic flux).

Doping of the ZnGeAs2 semiconductor with manganese has produced compositions with spontaneous magnetization and high Curie temperatures of up to 367 K for the composition 3.5 wt% Mn. Their magnetic properties are characteristic of spin glasses at temperatures T < T S and magnetic fields H < 11 kOe. In stronger fields, the spin glass state transforms into a phase with a spontaneous magnetization 4–5 times weaker than that to be expected under ferromagnetic ordering of all Mn ions. This is obviously a singly-connected ferromagnetic phase containing regions with frustrated bonds. The frustrated regions and the spin glass phase have inclusions of noninteracting ferromagnetic clusters, because these regions and the spin glass phase at low temperatures exhibit a strong increase in the magnetization M, with the dependence M(T) being described by the Langevin function. Measurements of the electrical resistivity ρ and the Hall effect have revealed that, for T < 30 K, the resistivity ρ of compositions with 1.5 and 3.5 wt % Mn is higher that at 30 K, which makes superexchange dominant and gives rise to the onset of the spin glass state. The nonuniform distribution of Mn ions in the spin glass phase accounts for the existence of isolated ferromagnetic clusters, their ferromagnetism being generated by carrier-mediated exchange. As the temperature increases still more, the increase in the mobility occurs faster than the decrease in the concentration, thus promoting an enhancement of the carrier-mediated exchange and growth of the ferromagnetic clusters in size, which at T = T S come in contact. This signifies a transition from a multiply-to a singly-connected ferromagnetic phase, which contains microregions with frustrated bonds.

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...

Solid solutions Cd1−x MnxGeP2 (x=0−0.19) have been synthesized and identified. In these solutions, the unit cell parameters decrease with an increase in the manganese content. The solid solution Cd0.81Mn0.19GeP2 is a ferromagnet with the Curie temperature T C ≈ 311 K. The paramagnetic moment of Mn2+ ions equal to 5.8 μB, as well as the spontaneous magnetization constituting 76% of the total magnetization of a crystal, has been determined with the use of the Langevin function. The origin of ferromagnetism in CdGeP2:Mn is exchange mediated by charge carriers (holes). These holes are caused by cationic defects in the structure of chalcopyrite.

Ferromagnetism is found in the CdGeAs 2 chalcopyrite doped by Mn. The Curie point of these materials achieves 355 K that is the highest one in A II B IV C V 2 :Mn systems. These systems are heterogeneous magnets and they consist of ferromagnetic and superparamagnetic phases. The volume of the first phase increases with a level of doping. An origin of ferromagnetism in CdGeAs 2 :Mn can be related to the existence of vacancies in (Cd, V C , Mn) GeAs 2 or non-stoichiometry of (Cd, Ge, Mn) GeAs 2 .

Ferromagnetism is found in the CdGeAs2 chalcopyrite doped by Mn. The Curie point of these materials achieves 355 K. This is the highest Curie point in AIIBIVCV2:Mn systems. These are heterogeneous magnets, they consist of a ferromagnetic and superparamagnetic phases. Portion of first phase increases with a level of doping. An origin of ferromagnetism in CdGeAs2:Mn is connected with the existence of vacancies (Cd, VC, Mn)GeAs2 or non-stoichiometric (Cd, Ge, Mn)GeAs2, as only in this case the ferromagnetic state is more advantageous than a spin glass-like state on theoretical estimations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A doped manganite with the composition Eu0.55Sr0.45MnO3 exhibits giant negative magnetostriction and colossal negative magnetoresistance at temperatures in the vicinity of the magnetic phase transformation (T∼41 K). In the temperature interval 4.2 K≤T ≤40 K, the isotherms of magnetization, volume magnetostriction, and resistivity exhibit jumps at the critical field strength H c1, which decreases with increasing temperature. At 70 K ≤T ≤120 K, the jumps on the isotherms are retained, but the shapes of these curves change and the H c1 value increases with the temperature. At HH c1, the magnetoresistance becomes negative, passes through a minimum near 41 K and then reaches a colossal value. The observed behavior is explained by the existence of three phases in Eu0.55Sr0.45MnO3, including a ferromagnetic (in which the charge carriers concentrate due to a gain in the s-d exchange energy) and two antiferromagnetic phases (of the A and CE types). The volumes of these phases at low temperatures are evaluated. It is shown that the colossal magnetoresistance and the giant volume magnetostriction are related to the ferromagnetic phase formed as a result of the magnetic-field-induced transition of the CE-type antiferromagnetic phase to the ferromagnetic state.

Magnetic, elastic, magnetoelastic, transport, and magnetotransport properties of the Eu0.55Sr0.45MnO3 ceramics have been studied. A break was detected in the temperature dependence of electrical resistivity ρ(T) near the temperature of the magnetic phase transformation (41 K), with the material remaining an insulator down to the lowest measurement temperature reached (ρ=106 Ω cm at 4.2 K). In the interval 4.2≤T≤50 K, the isotherms of the magnetization, volume magnetostriction, and ρ were observed to undergo jumps at the critical field H C1, which decreases with increasing T. For 50≤T≤120 K, the jumps in the above curves persist, but the pattern of the curves changes and H C1 grows with increasing T. The magnetoresistance Δρ/ρ = (ρ H −ρ H=0)/ρ H is positive for HH C1, the magnetoresistance is negative, passes through a minimum near 41 K, and reaches a colossal value of 3×105 % at H=45 kOe. The volume magnetostriction is negative and attains a giant value of 4.5×10−4atH=45 kOe. The observed properties are assigned to the existence of three phases in Eu0.55Sr0.45MnO3, namely, a ferromagnetic (FM) phase, in which carriers are concentrated because of the gain in s-d exchange energy, and two antiferromagnetic (AFM) phases of the A and CE types. Their fractional volumes at low temperatures were estimated to be as follows: ∼3% of the sample volume is occupied by the FM phase; ∼67%, by the CE-type AFM phase; and ∼30%, by the A-type AFM phase.

Colossal magnetoresistance (MR) and giant negative volume magnetostriction (MS) have been observed in the Curie temperature region of Sm1−xSrxMnO3 manganites for x=0.33 compounds containing ferromagnetic (FM) and A-type antiferromagnetic (AFM) clusters, and for x=0.4 and 0.45 containing FM and both types of AFM clusters (A type and charge ordering (CO) type). For x=0.33 magnetization, MR and MS increase smoothly with magnetic field increase and saturation of MR and MS is not achieved. For x=0.4 and 0.45 the sharp jump of magnetization, MR and MS takes place at HC1 HC2. We believe that the reason for colossal MR and giant MS being observed in the investigated compounds is the increase of FM phase volume under magnetic field action. For x=0.33 this increase is smooth because it arises from the FM phase “sprouting” on FM layers of the A-type AFM phase. For x=0.4 and 0.45 the increase of FM part volume arises from CO clusters with CE type of AFM structure too. In this case, CO clusters are completely transformed to the FM state. This transition is accompanied by crystal structure reconstruction that is manifested in both the temperature and magnetic field dependences of the anisotropic MS.

It is found that samples of manganites La0.9Sr0.1MnO3 (single crystal), Eu0.7A0.3MnO3 (A=Ca, Sr; ceramics), and La0.1Pr0.6Ca0.3MnO3 and La0.84Sr0.16MnO3 (thin epitaxial films) that are either field-cooled (in a magnetic field) or zero-field-cooled differ in low-temperature magnetization, and the hysteresis loop of field-cooled samples exhibits a displacement. This displacement signifies that a ferro-antiferromagnetic state occurs in these samples. The exchange integral J∼10−6 eV is calculated from this displacement, which describes the exchange Mn-O-Mn coupling through the interface ferromagnetic droplet-antiferromagnetic matrix. The magnetoresistance and volume magnetostriction of La1−x SrxMnO3 single crystals exhibit similar dependences on x, temperature, and the magnetic field in the vicinity of the Curie point, which points to the fact that these dependences are due to the same reason, namely, the occurrence of a magnetic two-phase ferro-antiferromagnetic state caused by strong s-d exchange.

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.

An experimental study of thermopower, magneto thermopower, magnetoresistivity and magnetization of Nd(1-x)SrxMnO3 and Sm(1-x)SrxMnO3 with 0 ≤ х ≤ 0.3 was conducted. A steep rise of thermopower as well as giant values of magneto thermopower and magnetoresistivity were observed near Curie temperature ТС in compounds with 0.15 ≤ х ≤ 0.3. On the other hand, no special features were found in case of х = 0. It has been known that compounds with 0.1 ≤ х ≤ 0.3 consist of ferromagnetic clusters of ferron (magnetic polaron) type located in A-type antiferromagnetic matrix. An increase of thermopower near ТС is caused by ferrons as with the application of magnetic field or temperatures higher than ТС thermopower falls sharply due to the destruction of ferrons. So, the value of thermopower is directly connected to the number of magnetic polarons in sample. Therefore, thermopower in doped magnetic semiconductors is determined by level of doping and volume of the sample.

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.

The parallel λ∥ and perpendicular λ⊥ magnetostriction (with respect to the applied magnetic field) and the thermal expansion Δl/l are studied on La1−xSrxMnO3 single crystals with x=0.1, 0.15, and 0.3. For the conducting sample with x=0.3 and the semiconducting sample with x=0.15 the volume magnetostriction (ω=λ∥+2λ⊥) is negative and the |ω|(T) curves go through a maximum at the Curie point TC. At T>TC its Δl/l temperature dependence is stronger than linear. For the semiconducting sample with x=0.1, ω is negative at T

The magnetic and electrical properties of new compounds having spinel structure Fe1−x Cr2(1−x)Sn2x S4 (0.1⩽x⩽0.33) (system 1), Fe0.67 [Fe0.165CrSn0.835]S4, and Fe0.67 [Fe0.33Cr0.67Sn]S4 has been studied. These compounds are p-type semiconductors with magnetic properties characteristic of the following magnetic-order types: ferrimagnetic (the x=0.1 composition of system 1), spin glass (the x=0.33 composition of system 1 and Fe0.67 [Fe0.165CrSn0.835]S4), and reentrant spin glass (the x=0.2 composition of system 1 and Fe0.67 [Fe0.33Cr0.67Sn]S4). For the spin-glass compositions, the dependence of the freezing temperature T f defined as the temperature of the maximum of initial magnetic susceptibility, on temperature and magnetic field obeys the Almeida-Thouless relation, and the dependence of T f on magnetic-field frequency is a power-law function. For the spin-glass and reentrant spin-glass compositions, a large peak in the absolute value of negative isotropic magnetoresistance was found near T f , which becomes as high as 15% in spin glasses and 30% in reentrant spin-glass compositions. In compositions with reentrant behavior, the activation energy of conductivity in the region of T f was found to change by about two orders of magnitude. This experimental evidence suggests that the spin-glass-paramagnet (in spin glasses) and spin-glass-long-range magnetic-order transformations are actually phase transitions, and that the spin-glass region contains ferron-type ferromagnetic clusters. These are the first spin-glasses among the chalcospinels with magnetically active ions on the tetrahedral and octahedral sublattices.

New ferromagnets with high Curie temperatures, reaching 355 K, have been obtained by doping a GdGeAs2 semiconductor compound with manganese. The obtained compounds are magnetically inhomogeneous, comprising a mixture of ferromagnetic (FM) and paramagnetic phases. The volume fraction of the FM phase increases with the degree of doping. The development of ferromagnetism in this system is probably related to the presence of vacancies of the (Cd, VC, Mn)GeAs2 type or to a nonstoichiometry of the (Cd, Ge, Mn)GeAs2 type, since theoretical estimates show that the FM state is energetically more favorable than the spin glass state only in these cases.

The magnetocaloric effect ΔTex and the magnetization in La1−xSrxMnO3 single crystals (x=0.1, 0.125, 0.175, 0.3) have been experimentally studied. The magnetic entropy and the magnetocaloric effect ΔTth were computed from magnetization curves. All the samples exhibited a maximum in the ΔTth(T) curve at T=Tmax′. A step was observed on the ΔTex(T) curve in the region of Tmax′, with the value of ΔTex on this step being substantially smaller than ΔTth. The step on the ΔTex(T) curve was followed by a maximum, which appeared at a temperature 20–40 K above Tmax′. This anomalous behavior of ΔTex and ΔTth is assigned to the coexistence of two magnetic (ferro-and antiferromagnetic) phases in the crystal. The calculated value of ΔTth is determined primarily by the ferromagnetic part of the crystal and disregards the negative contribution from the antiferromagnetic part of the crystal to ΔTex.

New type of magnetic nanomaterials is described. These are the ferromagnetic nanoregions (ferrons) in antiferromagnetic and ferromagnetic semiconductors near Curie point with a giant red shift of the band-gap, the nanoregions with destructive magnetic ordering in ferromagnetic semiconductors with the giant blue shift of the band-gap (antiferrons) and the nanoregions with layered antiferromagnetic order in semiconductors in which the most part of spins has antiferromagnetic order (afmons). Namely these nanoscale regions hold responsible for the giant effects of a magnitoresistance and a volume magnetostriction and for peculiarities of magnetic and another properties.

Mn-doped polycrystals and single crystals of CdGeAs/sub 2/ have been synthesized by chemical technology and their semiconducting and magnetic properties were studied. Starting from around 3 mole% and above the Mn-ions begin to occupy the Ge/sup 4+/ sites, the complexes Mn/sup 2+/ +2p with weak bound holes p supply the hh in a valence band. This is confirmed by ESR, synchrotron measurements and X-ray analysis. Ferromagnetism was observed in samples at 3 and 6%Mn. In why-type samples, ferromagnetism is derived from the kinematic exchange between Mn/sup 2+/ + p complexes, while in (CdGe,Mn)As/sub 2/, ferromagnetism is governed by the kinematic exchange between Mn/sup 2+/ + 2p complexes mainly on the Ge-sites via empty states near the top of the valence band.

Summary form only given. Eu/sub 1-x/Sr/sub x/MnO/sub 3/ series is scantly explored among manganites. This series is intriguing because unlike the other manganites, compounds with 0 /spl les/ x /spl les/ 0.5 are semiconductors and show ferromagnetic (FM) behaviour around x = 0.4. In this work we have studied magnetic, elastic, magnetoelastic, transport and magnetotransport properties of Eu/sub 0.55/Sr/sub 0.45/MnO/sub 3/ ceramic and have found the close relation between them. We find that Eu/sub 0.55/Sr/sub 0.45/MnO/sub 3/ is a heavily doped AFM semiconductor EuMnO/sub 3/ in which, as we propose, an inhomogeneous magnetic state is realized.

Summary form only given. The interest in the perovskite Mn oxides is associated with a colossal magnetoresistance (CMR) that was observed in certain compounds near room temperature. Some authors think that CMR is bound up with magnetic two-phase ferromagnetic-antiferromagnetic state in these materials. We investigate the magnetic properties of La/sub 0.9/Sr/sub 0.1/MnO/sub 3/ single crystal, La/sub 0.7/A/sub 0.3/MnO/sub 3/ (A = Ca, Sr) ceramic and La/sub 0.1/Pr/sub 0.6/CaO/sub 3/MnO/sub 3/ and La/sub 0.84/Sr/sub 0.16/MnO/sub 3/ epitaxial films which testify to the ferromagnetic-antiferromagnetic state in these samples. All the samples have the temperature dependence of electrical resistivity of semiconducting type and CMR in the Curie point region.

Thermopower α and magnetothermopower ∆α/α were studied in the single-crystal Sm 0.55 Sr 0.45 MnO 3 samples, containing clusters of following three types: ferromagnetic clusters with the Curie temperature T C = 134 K, A-type antiferromagnetic clusters with the Neel temperature T NA ≤ T C and CE-type antiferromagnetic clusters with the T NCE = 240 K. Temperature dependence of α and ∆α/α have extrema in the T NCE -region: large maximum on α (T) and sharp minimum on {∆α/α} (T) . Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field H = 13,2 kOe. As will be shown below thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order (CO), displacing oxygen ions. Modified crystalline lattice inside clusters causes change of thermopower in them. This thermopower influences on the voltage drop on sample at measurement of thermopower and, consequently, on the effective value α of the whole sample. Enclosure of the magnetic field in the T NCE , which accelerates the destruction of the CE-type antiferromagnetic order, causes sharp decrease of total thermopower. This means that the CE-type antiferromagnetic clusters with CO order are the main contributors to the thermopower of the whole sample.

Magnetocaloric effect (MCE) or T-effect was studied in La1-xSrxMnO3, Sm0.55Sr0.45MnO3 and PrBaMn2O6 manganites. It has been found that the maximum value of MCE, measured by direct method, is far less than obtainable by computation from the change of the magnetic entropy in Curie temperature TC. This phenomenon is explained by presence in them of the magnetic two-phase ferromagnetic (F) – antiferromagnetic (AF) state. So in La1-xSrxMnO3 the negative contribution from AF portion of sample lowers MCE and displacesmaximum on T(T)-curve to the higher temperature than TC on 20-40 K. Maximum on T(T) curve of Sm0.55Sr0.45MnO3 is disposed near TC=134 K in the cooling in the air single-crystal and ceramic samples. The cooling inoxygen of single-crystal,restored the Mn-O-Mn broken connections, increases the volume of clusters with CE-type of AF order, results to that maximum on T(T) curve is disposed at Neel temperature TN of this phase (243 K). Magnetic field, applied to sample during T-measurement, transforms AF clusters into F state and theboth types of clusters decompose at TN. The PrBaMn2O6 manganite has two phase transactions: paramagnetic–F at TC=295 K and F–AF at TN=231 K. Phase with spontaneous magnetization obtains the understated magnetic moment. Curve T(T) has the wide maximum near TC and the sharp minimum near TN with the small T-values in both extremes: 0,13 K and - 0,2 K respectively. This is connected with presence of AF interactions in F phase and F interactions in AF phase.

Magnetocaloric effect (ΔT-effect) was studied by straight method in two samples of Sm0.55Sr0.45MnO3 manganite: ceramic sample and single crystal, annealed in air atmosphere. The temperature dependence of ΔT-effect ΔT(T) of both of these samples has maximum at Tmax equal to 143.3 K for single crystal sample and 143 K for ceramic sample. In these maxima ΔT-values are 0.8 K for the former and 0.4 K for second samples. In addition the ΔT(T) curve of single-crystal sample has minimum at Tmin = 120 K and ΔT-value in minimum equal to - 0.1 K. The maximum value of ΔT-effect increases with H up to the maximum field of measurement 14.2 kOe. At this takes place the rate of this increasing is more at H > 8 kOe than at H < 8 kOe. The above listed peculiarities of ΔT-effect are explained of presence in samples of ferromagnetic, antiferromagnetic A-type and antiferromagnetic CE-type clusters.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behaviour of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behaviour. For T ≤ 15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4th period. Elements with superconductivity, by which d-shells start to fill up, are at the beginning of each period; then follow antiferromagnetics and ferromagnetics (in 4th period and lanthanides), or elements without any of the three listed order types (5th period and 6th period), in which the d (f)-shells continue to fill up almost exceedingly; then again appear superconductors by filling the p-shell up to the number is equal to 4. We calculated the radii of the external d (f)- and p-orbitals and the nearest to them orbitals with the Slater method. These trends were explained by distinction of degree of division of the external d (f)- or p-orbitals of the neighboring atoms in the crystal. Largest division occurs in ferromagnetics. In antiferromagnetics it is smaller than in ferromagnetics. It is demonstrated that in the superconducting crystals the external dor p-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals. Furthermore the external d- or p-shells of some elements in the 5th and 6th periods approach the deeper shells of neighboring atoms. Hence the electron in this shell is situated in neighboring atoms in a different electric field from its own. This fact is open to speculation that the separation of spin and charge in electron, disposed on the external d- or p-orbitals, is quite possible. The charges without spin become bosons. Spins that have the magnetic moments are ordered antiparallel in pairs. Magnetic field transfers this pair in a parallel state and a magnetic flux component along of magnetic field from the pair is equal to one fluxon (the quant of the magnetic flux).

The first thin La1−xAgyMnO3 epitaxial films (y ≤ x) were grown on SrTiO3 (110) substrates with silver present in the ionized state (Ag+) only. The Curie temperatures TC of the compositions with x = y = 0.05, x = y = 0.1, and x = 0.3 and y = 0.27 crystallizing in the hexagonal structure \(R\bar 3c\) above or close to room temperature. The temperature dependences of electrical resistivity ρ and of magnetoresistance ¦Δρ/ρ/¦ = ¦(ρH − ρ H = 0)/ρH=0¦ pass through maxima near TC, with the magnetoresistance being negative and reaching colossal values of ∼7–20% in a magnetic field H = 8.2 kOe not only at TC but also at room temperature. The magnetic moment per formula unit as derived from the saturation magnetization at T = 5 K is substantially smaller than expected for complete ferromagnetic ordering. The magnetization in fields of up to 6 kOe depends on the actual sample cooling conditions, and the hysteresis loop of a field-cooled sample is displaced along the H axis by ΔH. The above properties can be accounted for by the fact that the films are in a two-phase magnetic (ferromagnetic-antiferromagnetic) state induced by strong s-d exchange. The maximum value of Δ H was used to calculate the energy of exchange coupling between the ferromagnetic and antiferromagnetic parts of a sample.

To date, spin glass state is observed in chalcogenide spinels with magnetic ions either in tetrahedral A sublattice or in octahedral B sublattice. The possibility of spin glass state in chalcospinels with magnetic ions in both of A and B sublattices is not evident because the intersublattice antiferromagnetic superexhange is more higher than intrasublattice ferromagnetic superexhange. In the present paper the magnetic and electrical properties of first produced spinel Fe0.67Cr1.33Sn0.67S4 are studied. This sample is p‐type semiconductor. Here B sublattice is diluted of diamagnetic Sn4+ions and Fe2+ions deficiency exists in A sublattice. The isotherms of the magnetization σ are not saturated in investigation region of magnetic fieldH≤35 kOe and of temperatures 4.2≤T≤120 K. At the same time, this sample possesses magnetic properties typical of spin glass. Thus a maximum on the temperature dependence of the magnetic susceptibility measured in a weak ac field is founded at the freezing temperature T f . (The frequency region is 0.3≤ω≤2 kHz, H ∼=0.3 Oe.) The maximum is lowered under a static magnetic field which is applied parallel to the ac field. Low‐temperature magnetization in the weak field depends on the cooling process (with or without field). The T f (ω) dependence obeys the power law and T f (H,T) dependence obeys the Almeida–Touless relation; these facts attest that phase transition spin glass–paramagnetic exists in this sample. This is a first spin glass among chalcospinels with magnetic ions in A and B sublattices.

The dependence of magnetization, δ, and resistivity, ρ, on temperature T and magnetic field H has been studies near Curie point and at somewhat higher temperatures for single crystals of CdCr2Se4 deficient in selenium or doped with indium or copper. The magnetic field has a pronounced effect on the Tc values determined by extrapolation of the steepest section of the δ (T)‐ curves to the temperature axis. Thus, an increase of the field strength from 0.9 to 12.7 kOe leads to a 20 to 30° high temperature shift of the Curie point. The δ (H) curves measured near Tc are characterized by critical field values in the vicinity of which magnetization increases stepwise by about 80%. Copper doped crystals exhibit thermomagnetic hysteresis and those containing indium show positive magnetic resistivity in the temperature region where the critical field phenomena are observed. The experimental data are explained by the formation of ferrons, that is ferromagnetic microregions, under the action of magnetic field. The f erroas which owe their stability to the s‐d exchange and Coulomb attraction are supposed to be localized at non‐ionized impurity atoms. The magnetic field induced transition from a paramagnetic state to that characterized by the presence of ferrons represents the first‐order phase transition.