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Magnetotransport properties of spin-glass-like Ge1-x-ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083≤x≤0.142 and 0.012≤y≤0.119 are presented. The observed negative magnetoresistance we attribute to two mechanisms, i.e., weak localization occurring at low fields and spin disorder scattering giving contribution mainly at higher magnetic fields. A pronounced hysteretic anomalous Hall effect (AHE) was observed. The estimated AHE coefficient shows a small temperature dependence and is dependent on Mn-content, with changes in the range of 10-7

It has been shown that the overlap of tails of the density of states of the valence and conduction bands leads to the formation of a 'negative' gap in the InO-SrO ceramic with disordered structure and oxygen clusters in nanovoids. Two types of magnetism are observed. One of them caused by the formation of (dangling bond + O center) complexes has been found in samples saturated with oxygen. The other is associated with the presence of dangling bonds in oxygen-depleted samples. At T < 90.18 K, when oxygen molecules fall from the walls of nanovoids, small liquid oxygen droplets are formed with the release of a large number of free dangling bonds resulting in the variation of magnetization and electrical conductivity of samples. The effects caused by magnetic phase transitions in clusters of crystal oxygen are manifested at T < 54.8 K. The variations of the resistance of samples in the interval T = 5-300 K correspond to Mott's law under the dependence of the local activation energy for electron hopping on the state of oxygen clusters. [ABSTRACT FROM AUTHOR]

The Mn 2− x Fe x P 0.5 As 0.5 compounds ( x = 0.7 and 1.0) studied exhibit the magnetic phase transitions, which are accompanied by a magnetic entropy change. For x = 1 the PM–FM transition is of the first order one with a weak (2–3 K) thermal hysteresis in the vicinity of T C = 275 K. The Mn 1.3 Fe 0.7 P 0.5 As 0.5 compound possesses two magnetic transitions: the second-order PM–FM transition at T C = 190 K, followed by the FM–AFM transition at T N = 90 K, leading to normal and inverse magnetocaloric effects, respectively. The maximum values of magnetic entropy change are equal to 17 J kg −1 K −1 in MnFeP 0.5 As 0.5 and 5 J kg −1 K −1 in Mn 1.3 Fe 0.7 P 0.5 As 0.5 for a field change of 5 T. The magnetic entropy changes were calculated using both the isofield magnetization curves versus temperature and the isothermal magnetization curves versus applied magnetic field. The magnetocaloric effect in MnFeAs 0.5 P 0.5 is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius–Clapeyron equation. [ABSTRACT FROM AUTHOR]

Pressure effect on magnetic properties of polycrystalline La1-xBaxCoO3 (0.1 ⩽ x ⩽ 0.5) was studied by magnetization measurements in the temperature range 5-240 K, magnetic field up to 16 kOe, and under hydrostatic pressure up to 10.5 kbar. For low-doped cobaltites (x 0.1,0.15), it was found that applied pressure enhances the ferromagnetic (FM) cluster phase, resulting in an increase of both spontaneous FM moment and transition temperature of clusters TCcl, while the freezing temperature Tf lowers under pressure appreciably (dTf/dP ≈ -1.4 K/kbar), suggesting the weakening of interaction between clusters. For higher-doped La1-xBaxCoO3 (0.2 ⩽ x ⩽ 0.5), having developed long-range FM order, the systematic increase of Tc under pressure was observed with coefficient dTc/dP linearly increasing with doping up to 1.8 K/kbar at x = 0.5, the highest value reported for cobaltites. The positive value of the dTc/dP coefficient found for the Ba compound in a whole range of studied doping is in strong contrast to that found in Ca and Sr cobaltites, where the dTc/dP was found to change a sign from a negative to a positive one with increasing doping. It is shown that the sign reversal of the dTc/dP coefficient for La1-xMxCoO3 (M = Ca,Sr,Ba) cobaltites can be caused by the hole doping and also, independently, by the lattice expansion only induced by an increase of the dopant ion size. The complex pressure effect on ferromagnetic transition Tc in cobaltites is well described in terms of competing eg-electron bandwidth Wand crystal-field splitting energy, basing on the known pressure variations of the stenc factors. For La1-xBaxCoO3 with x = 0.3,0.5, having a high enough concentration of intermediate spin Co states, we observed a Jahn-Teller-like magnetic transition signified by a distinct hysteresis in field-cooled magnetization below Tc. This transition was found to disappear under moderate applied pressure, evidenced for La0.7Ba0.3CoO3 by abrupt changes in the spontaneous magnetization and coercive field at 5 K. [ABSTRACT FROM AUTHOR]

Magnetic and electron paramagnetic resonance (EPR) properties of EuFe(BO) single crystals have been studied over the temperature range of 300-4.2 K and in a magnetic field up to 5 T. The temperature, field and orientation dependences of susceptibility, magnetization and EPR spectra are presented. An antiferromagnetic ordering of the Fe subsystem occurs at about 37 K. The easy direction of magnetization perpendicular to the c axis is determined by magnetic measurements. Below 10 K, we observe an increase of susceptibility connected with the polarization of the Eu sublattice by an effective exchange field of the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the c axis, we have observed an increase of magnetization at T < 10 K in the applied magnetic field, which can be attributed to the appearance of the magnetic moment induced by the magnetic field applied in the basal plane. According to EPR measurements, the distance between the maximum and minimum of derivative of absorption line of the Lorentz type is equal to 319 Gs. The anisotropy of g-factor and linewidth is due to the influence of crystalline field of trigonal symmetry. The peculiarities of temperature dependence of both intensity and linewidth are caused by the influence of excited states of europium ion (Eu). It is supposed that the difference between the g-factors from EPR and the magnetic measurements is caused by exchange interaction between rare earth and Fe subsystems via anomalous Zeeman effect. [ABSTRACT FROM AUTHOR]

We present results of dc magnetic susceptibility measurements in TbBaCo4O7 single crystals performed at temperatures in the range 2-300 K and in magnetic fields up to 55 kOe. The results obtained seem to suggest that the ground state of TbBaCo4O7 is composed of coexisting long-range ordered and short-range ordered clusters and is transformed into a magnetically ordered weak ferromagnetic phase by application high magnetic field along c-axis. [ABSTRACT FROM AUTHOR]

In this review we briefly discuss the magnetocaloric properties of the manganites. It is evidenced that the maximum entropy change observed in manganites exceeds that of gadolinium (the prototype material for room temperature refrigerators). For the manganites characterized by second-order magnetic phase transitions the scaling hypothesis is discussed. It is shown that simple phenomenological model with only one fitting parameter, presented in this paper, satisfactorily describes experimental observations. [ABSTRACT FROM AUTHOR]

The principles of magnetic cooling and the magnetocaloric properties of various magnetic compounds have been presented with a special focus on materials with giant and colossal magnetocaloric parameters. The magnetocaloric properties of manganites and cobaltites have been considered. The maximum entropy change in polycrystalline La0.7Ca0.3MnO3 for the field of 2 T reaches 8 J ⋅ kg -1 ⋅ K-1, exceeding that of gadolinium. It is suggested that the rnanganites with superior magnetocaloric properties and low material costs are attractive magnetic refrigerator materials for technical applications. [ABSTRACT FROM AUTHOR]

Magnetic and electrical properties of La1−xSrxMnO3 (x=0.1, 0.15 and 0.3) single-crystals, Eu0.7A0.3MnO3 (A=Ca, Sr) ceramics, and La0.84Sr0.16MnO3 and La0.1Pr0.6Ca0.3MnO3 epitaxial thin films are investigated. Curves of T-dependence of the electrical resistivity and the magnetoresistance show the maxima near Curie point and magnetoresistance is colossal in maximum. Distinction between the magnetizations and the remanences of zero-field-cooled and field-cooled sample and displacement of hysteresis loop of field-cooled sample are found in La0.9Sr0.1MnO3 single-crystals, Eu0.7A0.3MnO3 (A=Ca, Sr) ceramics, and La0.84Sr0.16MnO3 and La0.1Pr0.6Ca0.3MnO3 epitaxial thin films. This displacement denotes that magnetic two-phase ferro–antiferromagnetic state is inherent in them. From this displacement the exchange integral &z.sfnc;J&z.sfnc;=10−7−10−6 eV, described the Mn–O–Mn connection across droplet/host interface, is calculated. The presence of ferromagnetic (F) and antiferromagnetic (AF) states in Eu0.7A0.3MnO3 (A=Ca, Sr) is confirmed by next facts: magnetization isotherms at T (TN is Neel temperature) are superposition of linear part, as for AF, and small spontaneous magnetization due to the F droplets; paramagnetic Curie point is approximately three times as much than in EuMnO3, whereas TN is slightly varied. Behavior of electrical and magnetic properties are explained by presence of magnetic two-phase F–AF state due to strong s–d exchange. [Copyright &y& Elsevier]

Recently, the crystal structure of synthetic and natural Cu-O compounds was analyzed in the unified classification scheme. Structural units of cuprates as salts of hypothetical copper acids were distinguished and assumed to be responsible for characteristic physical properties of these Cu-O compounds. In this work the optical and magnetic properties were studied in a series of synthetic and natural cuprates. The fine structure in the optical spectra of (M2Cu2O3)m(CuO2)n, CuGeO3, linarite PbCu(OH)2(SO4) and malachite Cu2(OH)2CO3 and other Cu-O compounds was correlated to the electronic excitations in particular structural units typical of cuprates. The temperature dependence of magnetic susceptibility was investigated on a series of Cu oxysalt minerals. The dimerization of magnetic moments was considered as a property, which was determined by the type of cuprate structural units. The observed relationship between the crystal structure and physical properties is useful in search of new magnetic materials. [Copyright &y& Elsevier]

Abstract: The effect of hydrostatic pressure on Curie temperature, the critical exponents and entropy change in La0.7Ca0.3MnO3 are determined. The pressure increases the Curie temperature. The combined magnetic entropy change, due to both magnetic field and pressure application, is found to be significant. It suggests that manganites are suitable candidates as barocaloric refrigerants near room-temperature region. [Copyright &y& Elsevier]

Abstract: This paper reviews experimental results concerning magnetic anisotropy in geometrically frustrated kagome staircase lattices. Following problems are discussed: high-temperature susceptibility measurements of kagome single crystals; inelastic neutron scattering measurements on Co3V2O8 single crystals; EPR of Co2+ ions in kagome staircase Mg3V2O8 single crystals. The single-ion anisotropy Hamiltonian is used to analyze experimental results. It is suggested that the magnetic anisotropy in kagome staircase M3V2O8 (M=Co, Ni, Mn) oxides has mainly single-ion origin. [Copyright &y& Elsevier]

Abstract: The effect of nonmagnetic Mg2+ and magnetic Co2+ doping in Kagome staircase compounds was investigated using DC magnetic susceptibility. The main effect of doping is to change effective anisotropy of the Ni3V2O8 and Co3V2O8 crystals. It has a considerable effect on magnetic field induced phase transitions in both kinds of crystals. The doping has also an effect on the Dzyaloshinskii–Moriya exchange interactions. In some cases the doping enhances this interaction while in another it suppresses it completely. [Copyright &y& Elsevier]

Magnetic and transport properties of Ge1-x-yMnxEuyTe crystals with chemical compositions 0.041⩽x⩽0.092 and 0.010⩽y⩽0.043 are studied. Ferromagnetic order is observed at 150

Phenomena occurring at the interface may significantly modify the properties of magnetic thin films. In this paper, the effect of temperature on the magnetic properties of Co(001)/MgO/Co trilayers is studied. The trilayer structure was modified by partial coverage of Co layers by Au at the Co/MgO interface. It is found that when the quantity of deposited gold is small, formation of islands at the Co/MgO interfaces takes place, which is proved by the topological surface analysis and by the x-ray reflectivity. In the investigated trilayer structure, gradual changes of the easy magnetization axis from the in-plane to the out-of-plane direction are observed during lowering the temperature from 300 to 5 K. The analysis of the ferromagnetic resonance spectra within the multiple-magnetic-layer model system indicates that the surface anisotropy provides a significant contribution to the magnetic anisotropy of complete Co(001)/MgO/Co heterostructure. [ABSTRACT FROM AUTHOR]

The frequency, temperature, and the dc and ac dependences of the magnetic susceptibility of the YbCoGaO4 and LuCoGaO4 single crystals are investigated. The YbCoGaO4 behaves like an Ising spin glass with a strong uniaxial anisotropy. In contrast LuCoGaO4 is Heisenberg-like spin glass. Dynamical scaling reveals a three dimensional phase transition near Tg and yields critical exponent values between those of Heisenberg- and Ising-like systems. [ABSTRACT FROM AUTHOR]

The frequency, temperature, and the dc and ac dependences of the magnetic susceptibility of the YbCoGaO4 and LuCoGaO4 single crystals are investigated. The YbCoGaO4 behaves like an Ising spin glass with a strong uniaxial anisotropy. In contrast LuCoGaO4 is Heisenberg-like spin glass. Dynamical scaling reveals a three dimensional phase transition near Tg and yields critical exponent values between those of Heisenberg- and Ising-Like systems. [ABSTRACT FROM AUTHOR]

The second-order anisotropy constant K2 in polycrystalline Gd5Si2Ge2 giant magnetocaloric material was measured as a function of temperature by the modified singular point detection technique. Although the structural, electrical, thermal, magnetic and magnetocaloric properties of the Gd5Si2Ge2 have been rather well investigated experimentally, magnetic anisotropy of this system is almost unknown. The singularity indicating the anisotropy field was determined analyzing ac susceptibility data taking into account several features of the magnetization curve. The temperature dependence of the anisotropy fields was measured from 4.2 K up to the Curie temperature. The observed relationship between K2(T)=K2(0) and magnetization M(T)=M(0) was explained assuming dipolar origin of magnetic anisotropy of Gd5Si2Ge2 compound. [ABSTRACT FROM AUTHOR]

Abstract: Magnetization and specific heat measurements have been performed for the S=3/2 antiferromagnet on a kagome staircase, Co3V2O8 single crystal as a function of temperature and magnetic field . Using these data the phase diagram was established on the H–T plane and compared with that determined for Ni3V2O8. The both phase diagrams are described by a model of competing first and second neighbor interactions and uniaxial anisotropy with the easy-axis magnetization along the a-axis . [Copyright &y& Elsevier]

The light emitting devices (LEDs) based on the p-Zn1-xMnxTe bicrystals have been fabricated. The Zn1-xMnxTe LEDs produce red and green emission originated from the internal d-shell transitions of the Mn2+ ions and the donor-acceptor-pairs recombination, respectively. The presence of the acceptor bound magnetic polarons and their clusters in the Zn1-xMnxTe crystals near the Curie–Weiss temperature was observed. It induces a critical behavior of the magnetic field dependence of the green emission intensity and a positive magnetoresistance in the Zn1-xMnxTe LEDs. [ABSTRACT FROM AUTHOR]

The contribution of clusters of different sizes to magnetism and the switching of electron scattering mechanisms in amorphous Fe67Cr18B15 alloy during ion Ar+ irradiation is studied. The cluster magnetism is found to be related to the presence of clusters of the following two types: large α-(Fe, Cr) clusters of size D = 150-250 Å and small (D = 40-80 Å) clusters in a random intercluster medium. The generation of small ferromagnetic and antiferromagnetic clusters during ion irradiation leads to the formation of cluster glass, which affects the electrical properties of the alloy and causes a magnetic frustration. The temperature dependence of the barrier height is shown to characterize the magnetic state of the alloy in low fields. On the whole, the temperature dependence of the order parameter is a universal characteristic of the system. The temperature dependence of resistivity of initial alloys in the temperature range 98-300 K (ρ(T) ∝ T2) is determined by electron scattering by quantum defects, and the transition into a ferromagnetic state is revealed when the derivative ∂ρ/∂T ∝ T is analyzed. The increase in resistivity and the relation ρ ∝ T1/2 in strongly inhomogeneous samples after irradiation at a dose Φ = 1.5 × 1018 ions/cm2 are caused by weak localization effects, and the transition to a ferromagnetic state becomes obvious when the derivative ∂ρ/∂T ∝ T-1/2 is considered. Irradiation by fluence Φ = 3 × 1018 ions/cm2 induces a giant (twofold) increase in the alloy density, restores the ferromagnetism of large clusters, decreases the resistivity by 37%, and restores the relation ρ(T) ∝ T2, which results from the overlapping of the irradiation-induced small clusters when their concentration increases and from an increase in the alloy density. The overlapping of clusters lowers the barrier height and decreases the sensitivity of the alloy to an applied field. The relation ρ(T) ∝ T2 is valid for the entire temperature range T = 2-300 K because of the partial screening of the magnetic moments of large clusters by a medium having the properties of cluster glass. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect in the vicinity of the martensitic transformation for a single crystalline alloy with a composition close to the stoichiometric Ni 2 MnGa has been determined indirectly by M ( T,H ) magnetization measurements. It has an inverse character. The magnetocaloric parameters, i.e., the magnetic entropy change, refrigeration capacity and various hysteretic effects have been calculated from the M ( T,H ) dependences. Besides the martensitic transition a weak entirely separated intermartensitic transition was observed. These two successive magneto-structural transformations give contributions to the observed magnetocaloric effect. Unusual dependence of entropy change as a function of magnetic field has been explained as arising because of two different mechanisms. Additionally, to confirm that studied martensitic transformation is a first order phase transition electrical resistivity and thermoelectric power measurements have been performed. [ABSTRACT FROM AUTHOR]

We show that in In 2 O 3 –SrO ceramics with disordered structure and oxygen clusters in nanovoids, the band tails of valence and conduction bands form “negative” gap. Two types of magnetism are observed. One of them caused by formation of the “dangling bond+O 2 − ion” centers has been found in the samples saturated with oxygen. Another type is associated with the presence of dangling bonds in the oxygen-depleted samples. At T <90.18 K, the liquid oxygen droplets of small size are formed with subsequent detachment of oxygen molecules from the walls of nanovoids emptying a considerable quantity of free dangling bonds resulting in the changes in magnetization and conductivity of the samples. At T <54.8 K, the effects related to magnetic phase transitions in the clusters of crystalline oxygen are observed. The changes in resistance of the samples in the range of T =5–300 K correspond to the Mott׳s law at a dependence of local activation energy on the phase state of oxygen clusters. [ABSTRACT FROM AUTHOR]

We present the studies of structural, electrical, and magnetic properties of bulk Sn 1 − x − y Cr x Eu y Te crystals with different chemical compositions varying in the range of 0.004 ≤ x ≤ 0.089 and 0.007 ≤ y ≤ 0.020. The structural characterization of our samples indicated the clustering of the Cr-ions into Cr–Te related clusters. Eu ions do not form clusters and are randomly distributed in the SnTe lattice. The magnetotransport studies show the presence of positive linear magnetoresistance with maximum amplitude of about 80% for all our samples. Positive magnetoresistance is a geometrical effect related to the presence of clusters in the SnTe lattice. The cluster-glass-like state at the temperature of about 130 K is observed for x ≤ 0.025. The cluster-glass-like state is due to the presence of Cr-rich clusters in the SnTe lattice. The ferromagnetic behavior with the Curie temperature of about 275 K is observed for the samples with x > 0.077 indicating the presence of Cr 5 Te 8 clusters in the host material. Eu ions presence in our samples shows paramagnetic behavior. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic properties of the kagome staircase compound Co3V2O8doped by 3-d elements (Mn, Mg and Zn) have been investigated using ab-initio FPLO method. We found that in the case of Mg and Zn the electronic densities of states near the Fermi energy is not significantly modified, however substitution the cobalt by manganese atom changed the band structure near the Fermi energy. [ABSTRACT FROM PUBLISHER]

We have studied the relation between clusterization in the flux of a substance and the thickness of deposited films obtained by the magnetron and pulsed laser sputtering of LaSrMnO and YBaCuO targets, respectively. No cluster formation has been observed in the case of magnetron sputtering, which is explained by a low concentration of atoms (ions) in the sputtered material flux. In accordance with calculations for the flux of non-interacting atoms, the deposited film thickness ( h) exhibits exponential decrease with increasing distance ( L) from the target. In the case of pulsed laser sputtering, for which the concentration of sputtered substance in the plasma is four orders of magnitude higher, the h( L) curve sharply deviates from the calculated dependence for the distances L > 6.2 cm, which is explained by the onset of intense clusterization in the laser plasma flux. [ABSTRACT FROM AUTHOR]

X-ray diffraction and magnetic measurements of polycrystalline and nanosize TbMnO3 manganites were performed. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature. Nanosize manganites were synthesized via the sol-gel method at different (800 and 900 °C) temperatures. The average size of the synthesized nanoparticles (from 45 to 70 nm) was estimated by x-ray diffraction and low-temperature adsorption of argon. Information about the evolution of properties of TbMnO3 with changing grain size, temperature, and magnetic field was obtained. Crystal structure parameters of nano-samples change slightly with changing nanoparticle size. Peculiarities of magnetic ordering in polycrystalline and nanosize TbMnO3 were compared. Magnetization and the Nèel temperature corresponding to antiferromagnetic ordering of the Tb3+ sublattice decrease as the particle size is reduced. Inverse magnetic susceptibility of the nanoparticle samples deviates from the Curie-Weiss law below 50 K; this is related to the magnetic ordering of Mn3+ moments. Some peculiar anomalities related to the magnetic ordering of Tb3+ and Mn3+ sublattices were noticed in specific heat values of the nanosize samples. [ABSTRACT FROM AUTHOR]

Abstract: We report the first observation of magnetic order above room temperature in zinc sulfide doped with Cu2+ made by a simple sintering process and detected by ferromagnetic resonance (FMR), SQUID magnetometry and the μSR experiments. FMR study shows nonzero absorption above room temperature indicating a high value of Curie temperature. Field-cooled and zero-field-cooled magnetization data indicate a bifurcation at about 300K. This temperature is considered to be the blocking temperature at ferromagnetic nanosized regions, which appear to exist in the sample of ZnS doped with copper. The muon spin rotation measurements confirm highly nonuniform magnetic order. It was shown that about 25% of the sample volume fraction exhibits strong magnetism. [Copyright &y& Elsevier]

A letter to the editor is presented on the topic of negative magnetization in a type of perovskite.

Abstract: LaCo0.5Fe0.5O3+d system has been prepared using different thermal treatments by conventional ceramic technology. The samples prepared at 1570K in air and below this temperature are mixtures of orthorhombic and rhombohedral phases. Increasing temperature up to 1670K stabilizes the rhombohedral phase whereas annealing in vacuumed quartz tube with a metallic getter results in orthorhombic single-phase structure. All the samples exhibit the ferromagnetic component at temperatures up to 360K as a result of Dzialoshinsky–Moriya interactions between the Fe3+ ions. The orthorhombic samples have a giant magnetic anisotropy, mostly associated with Co2+ ions. Co3+ ions are supposed to adopt a low spin state. [Copyright &y& Elsevier]

The structure, electrical, and magnetic properties of epitaxial LaCa(Sr)MnO single crystal films with a clustered structure have been studied. In films with a “metallic” phase content Cm0 ≤ 0.15, the electric conductivity is determined by the spin-dependent tunneling of charge carriers between “metallic” clusters, and the magnetoresistance is maximum at T = 4.2 K. The correlated motion of carriers over the system of tunneling-linked clusters leads to the formation of a window in the Coulomb blockade. The interactions between atomic, magnetic, and electron subsystems increase in the vicinity of the dielectric–metal percolation transition (T = 200–210 K), where the metal phase content Cm in the samples with Cm0 ≥ 0.2 reaches a maximum (Cmcrit = 0.5) due to an increase in the cluster size upon cooling. In this case, the magnetoresistance exhibits a maximum at T = 260 K, on the dielectric side of the percolation transition. Due to the presence of space charge regions at the periphery of the clusters, the content of a ferromagnetic phase is 1.5–2 times that of the “metallic” phase. For this reason, the calculations are performed using a model combining the tunneling conductivity mechanism with the percolation approximation for the description of magnetization. Allowance for the Coulomb interaction between charge carriers and clusters improves the agreement of theory and experiment. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Abstract: From the viewpoint of crystal chemistry, the chemical formula of strontium cuprate–borate (SCB) is represented as Sr[Cu2B2O6]. New data on the flux growth of SCB have been obtained. SCB single crystals with good quality have been successfully grown from Na2B4O7-based high-temperature solutions, as a result of lowering the temperature from 900 to 750°C at a cooling rate of 6–10°C/day. Their size increases with a lower cooling rate of the fluxed melt. Some SCB crystals displayed strongly developed growth striations on the {001} faces. Magnetic properties have been studied as a function of temperature and magnetic field. [Copyright &y& Elsevier]

The influence of photoillumination on the magnetic and transport properties of epitaxial thin films of the manganite Pr0.6La0.1Ca0.3MnO3 is investigated. It is found that illuminating films with He–Ne laser light increases their magnetization and decreases their electric resistance, stimulating an antiferromagnetic-insulator—ferromagnetic-metal phase transition, which is observed in this crystal in a magnetic field at low temperatures. It is shown that the phase-transition field is appreciably lower after the films are photoilluminated. It is concluded that photoillumination gives rise to the formation and growth of ferromagnetic metallic clusters inside an antiferromagnetic insulating phase. The mechanism of the effect of light on the magnetic and electric states of the manganite Pr0.6La0.1Ca0.3MnO3 could be related with photoinduced electron transfer from Mn3+ to Mn4+ ions, which results in melting of the charge ordering present in this manganite in the antiferromagnetic insulating state, and gives rise to a transition of the crystal into a ferromagnetic metallic phase. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have measured the temperature dependence of gap features revealed by Andreev reflection (Δ[sub s]) and by tunneling (Δ) in the ab plane of optimally and slightly overdoped microcrystals of (BiPb)[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 10+δ] (Bi2223) with critical temperature T[sub c]=110–115 K, and Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] (Bi2212) with T[sub c]=80–84 K. The tunneling conductance of a Bi2223-insulator-Bi2223 junction shows peaks at the 2Δ gap voltage, as well as dips and broad humps at other voltages. In Bi2223, similarly to the well-known Bi2212 spectra, the energies corresponding to 2Δ, to the dip, and to the hump structure are in the ratio 2:3:4. This confirms that the dip and hump features are generic to the high-temperature superconductors, irrespective of the number of CuO[sub 2] layers or the BiO superstructure. On the other hand, in both compounds the Δ(T) and Δ[sub s](T) dependences are completely different, and we conclude that the two entities are of different natures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Distinction between the magnetizations and the remanences of zero-field-cooled and field-cooled sample and displacement of hysteresis loop of field-cooled sample are found in La0.9Sr0.1MnO3 single crystals, Eu0.7A0.3MnO3 (A=Ca, Sr) ceramics, and La0.84Sr0.16MnO3 and La0.1Pr0.6Ca0.3MnO3 thin films. This displacement denotes that ferro–antiferromagnetic state is inherent in them. From this displacement we calculated the exchange integral &z.sfnc;J&z.sfnc;=10−7–10−6 eV, described the Mn&z.sbnd;O&z.sbnd;Mn connection across droplet/host interface. The behavior of CMR and volume magnetostriction near TC are similar in La1−xSrxMnO3 and explained magnetic two-phase state due to strong s–d exchange. [Copyright &y& Elsevier]

A study of the magnetization of the antiferromagnefic magnetoelectric crystal LiCoPO[sub 4] as a function of temperature and the strength of a magnetic field oriented along the antiferromagnetic vector reveals features due to the presence of a weak ferromagnetic moment. The value of the magnetic moment along the b axis at 15 K is approximately 0.12 G. The existence of a ferromagnetic moment can account for the anomalous behavior of the magnetoelectric effect observed previously in this crystal. [ABSTRACT FROM AUTHOR]

Abstract. Magnetization measurements of Ba[sub 0.6]K[sub 0.4]BiO[sub 3] single crystal have been performed to study the nature of the growth-induced anisotropy revealed using chemical etching technique. It was found that this anisotropy is responsible for differences in low-field susceptibility and in hysteresis loops observed for different magnetic field orientations. [ABSTRACT FROM AUTHOR]

We present the studies of electrical transport and magnetic interactions in Zn1-xMnxGeAs2 crystals with low Mn content 0≤x≤0.042. We show that the ionic-acceptor defects are mainly responsible for the strong p-type conductivity of our samples. We found that the negative magnetoresistance with maximum values of about -50% is related to the weak localization phenomena. The magnetic properties of Zn1-xMnxGeAs2 samples show that the random Mn-distribution in the cation sites of the host lattice occurs only for the sample with the lowest Mn-content, x = 0.003. The samples with higher Mn-content show a high level of magnetic frustration. Nonzero Curie-Weiss temperature observed in all our samples indicates that weak ferromagnetic (for x = 0.003) or antiferromagnetic (for x>0.005) interactions with the Curie-Weiss temperature, |Θ|<3 K, are present in this system. The Ruderman-Kittel-Kasuya-Yosida model, used to estimate the Mn-hole exchange integral Jpd for the diluted Zn0.997Mn0.003GeAs2 sample, makes possible to estimate the value of Jpd=(0.75 ± 0.09) eV. [ABSTRACT FROM AUTHOR]

The temperature dependences M(T) and field dependences M(H) of the magnetization have been measured in single-crystal TbBaCo4O7 for two magnetic-field directions: H∥c and H⊥c. In the case of H∥c, a magnetic field-induced irreversible transition is detected at low temperatures, accompanied by magnetization jumps on the M(H) dependences. It is shown that the transition field depends on the rate at which the external magnetic field is introduced. [ABSTRACT FROM AUTHOR]

The light emitting devices based on the p-Zn1-xMnxTe bicrystals have been fabricated. The Zn1-xMnxTe devices produce red and green emission originating from the internal d-shell transitions in the Mn2+ ions and the donor-acceptor pairs recombination, respectively. A critical behavior of the magnetic field dependence of the green emission intensity and a positive magnetoresistance near the Curie-Weiss temperature in the Zn1-xMnxTe devices was observed. [ABSTRACT FROM AUTHOR]

The magnetic properties of the site ordered multicomponent vanadate Mg3Fe4(VO4)6 are studied using dc magnetization and electron paramagnetic resonance (EPR) measurements. The static susceptibility shows antiferromagnetic interactions between Fe3+ spins with a Curie-Weiss temperature Θ=-111(1) K, while a transition to a spin-glass-like state is observed at T≈8.5 K, indicating appreciable spin frustration. EPR measurements corroborate the presence of antiferromagnetically coupled Fe3+ spins from high temperatures, while a distinct change in the temperature variation of the EPR parameters is observed at T<80 K, complying with the mean-field energy scale provided by the Curie-Weiss temperature of the system. The resulting magnetic inhomogeneity that persists despite the absence of cation disorder between magnetic and diamagnetic metal ions is attributed to the presence of small amounts of oxygen deficiency that modifies the connectivity and superexchange coupling between Fe3+ spins and leads to a disordered magnetic ground state. [ABSTRACT FROM AUTHOR]

The magnetic properties of γ-Fe2O3 ferrimagnetic nanoparticles embedded in a multiblock poly(ether-ester) copolymer have been investigated by static magnetization and ferromagnetic resonance (FMR) measurements at two different dispersion states. Significant variation of the magnetic response is identified below T≈120 K, most pronounced in the marked resonance field shift of the FMR spectra, independently of the dispersion state of the nanocomposites. This behavior correlates favorably with the dynamic relaxation of the copolymer, indicating a matrix freezing effect that is attributed to the magnetoelastic coupling of the oxide nanoparticles with the surrounding polymer. At low temperatures, the dc magnetization and FMR measurements vary considerably for the two nanocomposites, indicating essential differences in their ground state, related to the different morphology of the samples and the concomitant variation of interparticle interactions. [ABSTRACT FROM AUTHOR]

The magnetic properties of two biogenic polyamine copper complexes were investigated by dc magnetization and electron paramagnetic resonance (EPR) measurements. The variation in temperature of the low field magnetization reveals that the absence or presence of water molecules in the copper coordination sphere results, respectively, in the enhancement or suppression of antiferromagnetic interactions between Cu[SUP2+] ions. Analysis of the EPR spectra shows considerable temperature dependence of both the g values and EPR linewidths that persist in the paramagnetic regime for both complexes. Such variation of EPR parameters is attributed to the interplay of demagnetizing field effects, pertinent to the purely paramagnetic compound, and to the presence of short-range magnetic order that applies to the antiferromagnetic polyamine complex. [ABSTRACT FROM AUTHOR]

The properties of the TbBa(Co[sub 2-x]Fe[sub x-])O[sub 5+δ](00.1, at which a concentration-dependent orthorhombictetragonal transition takes place. The orthorhombic composition with x=0.1 exhibits a transition from an antiferromagnetic to weak ferromagnetic state at a temperature T[sub i]=200 K on warming and at 160 K on cooling, and a transition from a weak ferromagnetic to paramagnetic state at T[sub N] =304 K. A metal-insulator transition occurs at T[sub M]=348 K on warming. Transformation into a tetragonal phase (x ≥ 0.12) leads to the disappearance of both the weak ferromagnetic state and the metal-insulator phase transition. Also, the Néel point drops. The orthorhombic and tetragonal phases coexist in the concentrational range (0.1

The influence of hydrostatic pressure on magnetization, electrical conductivity and magnetoresistance of FeCr[sub 2]S[sub 4] single crystals has been studied. Significant pressure influence on the temperature of a spin-glass like magnetization anomaly, dT[sub m]/dp approx. 2.7 K/kbar, on the Curie temperature, dT[sub C]/dpapprox. 0.9 K/kbar, as well as on the resistivity and magnetoresistance, was found. The negative magnetoresistance maximum at the Curie temperature is shifted under pressure towards higher temperatures. Pressure induced changes of the low field magnetoresistance and of the conductivity anomalies at T[sub m] are correlated well with the changes in the magnetization. In the low temperature region the appearance of low symmetry anisotropy has been observed. This effect is distinctly enhanced by the hydrostatic pressure. The low symmetry component of magnetic anisotropy was suggested to be due to the static Jahn–Teller effect. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present studies of the influence of the chemical composition changes on the type of magnetic order present in bulk nanocomposite Ge 1− x−y Pb x Cr y Te crystals with the average Pb-content close to x  ≈  0.20 and Cr-content, y , varying from y  =  0.017 up to 0.043. Detailed magnetometric studies revealed the existence of two ordered magnetic states present in all our samples. All our crystals show a paramagnet to spin-glass-like state transition at temperatures from 135 K to 145 K, related to the presence of Cr 5 Te 8 clusters in the host lattice. The second transition type depends on the Cr-content, y . In the case of samples with y equal to 0.038 and 0.043 the ferromagnetic phase is observed with T C slightly below 70 K, while in samples with lower chromium concentration the presence of spin-glass-like state slightly below 50 K is observed. The presence of clusters in our samples has significant impact on the carrier transport and magnetotransport in our samples. The presence of critical scattering on the magnetic impurities is observed in resistivity and magnetoresistance data. Nearly-linear magnetoresistance is also observed in our samples indicating a presence of strong scattering on the grain boundaries in our samples. [ABSTRACT FROM AUTHOR]

We present studies of magnetotransport properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition changing from 0.180 < x < 0.311 to 0.019 < y < 0.136. Our samples show the presence of the cluster-glass-like transition accompanied with magnetic irreversibility at temperatures T SG around 90 K. The presence of strong anomalous Hall effect (AHE) with hysteresis is observed at T < T SG . The data analysis allowed calculation of a correction to the Hall constant R H for T < T SG and the AHE constant, R S . R S is around 10 −6 m 3 /C. R S and R H do not change strongly with temperature. The scaling law analysis has proved that the AHE in this system is due to the extrinsic mechanisms dominated by the skew scattering with relatively small contribution of the side jump process. Strong localization occurs in our system at T < T SG and causes a presence of a minimum in the resistivity vs. temperature dependence. The magnetoresistance of our samples shows complex behavior at T < T SG . The negative magnetoresistance is observed at T < 20 K and interpreted as spin-dependent scattering of conducting carriers on localized magnetic moments. At higher T nearly linear positive magnetoresistance is observed at temperatures from 20 K up to T ≈ T SG , where it reaches maximum. Positive linear magnetoresistance is related to the granular nature of our samples while the maximum near T SG is related to the giant spin-splitting of the valence band. [ABSTRACT FROM AUTHOR]

We show that сluster magnetism in ferromagnetic amorphous Fe 67 Cr 18 B 15 alloy is related to the presence of large, D =150–250 Å, α- ( Fe Cr ) clusters responsible for basic changes in cluster magnetism, small, D =30–100 Å, α -( Fe, Cr ) and Fe 3 B clusters and subcluster atomic α -( Fe, Cr, B ) groupings, D =10–20 Å, in disordered intercluster medium. For initial sample and irradiated one ( Φ =1.5×10 18 ions/cm 2 ) superconductivity exists in the cluster shells of metallic α-(Fe, Cr ) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ =3×10 18 ions/cm 2 , the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ ( T )~ T 2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ =1.5×10 18 ions/cm 2 , the transition to a dependence ρ ( T )~ T 1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ =3×10 18 ions/cm 2 , a return to the dependence ρ ( T )~ T 2 is observed. [ABSTRACT FROM AUTHOR]

We present studies of magnetic properties of Ge 1− x − y Pb x Mn y Te bulk crystals with chemical composition varying in the range of 0.180 < x < 0.311 and 0.019 < y < 0.136. Two transitions, one at temperatures below 20 K and the other between 44 and 105 K, are observed. The transitions are associated with the presence of two magnetic subsystems having different chemical compositions – the host lattice and clusters. The transition at higher temperatures is identified as a transition from a paramagnetic state to a spin-glass-like state. The observed magnetic order is interpreted in terms of the carrier mediated ferromagnetism, assuming an exchange interaction among magnetic ions in both subsystems. The experimental results are analyzed theoretically with good accuracy within the spin-wave-theory-based model of a disordered two-phase ferromagnet with the long-range Ruderman–Kittel–Kasuya–Yosida interaction. The magnetic exchange constant, J pd , having values from 0.47 eV to 0.80 eV gives spin-glass transition temperature, T SG , values close to the experimental values for the Ge-rich phase. The magnetic order observed for the Pb-rich phase is also due to the carrier mediated magnetic interaction. The experimental transition temperatures are fitted with J pd value ranging from 0.22 eV to 0.28 eV. [ABSTRACT FROM AUTHOR]