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Accurate thermal sensing with good spatial resolution is currently required in a variety of scientific and technological areas. Luminescence nanothermometry has shown competitive superiority in contactless temperature sensing, especially at the nanoscale. To broaden the use of such thermometers, development of a novel sensor type with high sensitivity and resolution is highly demanded. Herein, we report single-phase Ln3+-doped YVO4 nanophosphors synthesized using a modified Pechini method as multimode optical thermometers for wide-range temperature probing (299-466 K). The observed temperature-induced red shift of the charge transfer band was utilized to provide thermal sensing. Temperature sensing was based on the luminescence intensity ratio using emission intensities obtained upon charge transfer and direct lanthanide excitation, the spectral position of the charge transfer band and its bandwidth. The suggested probing strategies provided a high relative thermal sensitivity (up to 3.09% K-1) and a precise temperature resolution (up to 0.1 K). The obtained results can be useful for the design of novel contactless luminescence thermometers.

Achieving a combination of real-time diagnosis and therapy in a single platform with sensitive thermometry and efficient heat production is a crucial step towards controllable photothermal therapy. Here, Nd

Charge carriers parameters on a 2D-layer surface for (Cd1−x−yZnxMny)3As2 (y = 0.08) (the concentration n 2 D = 1.9 × 1012 cm–2, the effective value of the 2D-layer d 2 D = n 2 D / n 3 D = 14.5 nm, the wave vector k F = 0.1 nm–1, the charge carriers relaxation time due to dispersion τ D = 1.8 × 10–13 s, the velocity of charge carriers on Fermi surface v F = ℏ k F / m c = 2.65 × 105 m s−1, the mean free path l F = v F τ D = 47.7 nm) were determined. It was found that the dependence of the cyclotron mass m с (0)/m0 on Fermi wave vector k F for (Cd1−x−yZnxMny)3As2 (y = 0.08) is in compliance with a theoretical linear dependence, that describes mass-less Dirac fermions.

We report systematic study of Dy3+-doped YVO4 nanophosphors synthesized via modified Pechini technique. Effect of calcination temperature and doping concentration on structure and luminescence has been investigated. XRD and Raman spectroscopy revealed preparation of single phase nanoparticles without any impurities. Synthesized nanopowders consisted of weakly agglomerated nanoparticles with average size about 50 nm. Photoluminescence spectra of YVO4:Dy3+ nanoparticles consisted of the characteristic narrow lines attributed to the intra-configurational 4f-4f transitions dominating by the hypersensitive 4F9/2–6H13/2 transition. The calcination temperature variation did not affect 4F9/2 lifetime, whereas increase of doping concentration resulted in its gradual decline. Potential application of YVO4:Dy3+ 1 at.% and 2 at.% nanopowders as ratiometric luminescence thermometers within 298–673 K temperature range was tested. The main performances of thermometer including absolute and relative thermal sensitivities and temperature uncertainty were calculated. The maximum relative thermal sensitivity was determined to be 1.8% K−1@298 K, whereas the minimum temperature uncertainty was 2 K.

Shubnikov-de Haas (SdH) effect and magnetoresistance measurements of single crystals of diluted II-V magnetic semiconductors (Cd

We report on the potential application of NIR–to–NIR Nd3+-doped yttrium vanadate nanoparticles with both emission and excitation operating within biological windows as thermal sensors in 123–873 K temperature range. It was demonstrated that thermal sensing could be based on three temperature dependent luminescence parameters: the luminescence intensity ratio, the spectral line position and the line bandwidth. Advantages and limitations of each sensing parameter as well as thermal sensitivity and thermal uncertainty were calculated and discussed. The influence of Nd3+ doping concentration on the sensitivity of luminescent thermometers was also studied.

The phase formation sequence was studied in the preparation of solid solutions of RE2O2S: Ln’ (RE = La, Y; Ln’ = Ce, Eu, Dy, Er) by the reduction of the match co-precipitated sulfates, followed by sulfidization of the reduction products. For uniform distribution of cations in the matrix, a method of chemical homogenization was used, consisting in the preparation of an aqueous solution containing all the necessary cations and their subsequent precipitation in the form of sulfates. The use of sulfates as precursors facilitates the process of obtaining solid solutions of oxysulfides, since sulfates already contain SO42--ions. The phase and morphological certification of the obtained solid solutions was carried out. The study of steady state luminescent properties demonstrated characteristic bands which are assigned to 4f-4f and 5d-4f transition. The obtained results showed the possibility of applying the method to synthesize optical ceramics based on solid solutionsRE2O2S: Ln (RE = La, Y; Ln = Ce, Eu, Dy, Er).

Single crystals of the solid solutions CdGeAs2:Mn(x) and Cd0.964Zn0.036GeAs2:Mn(x) have been grown by the vertical Bridgman method. An X-ray diffraction study has demonstrated that Cd0.964Zn0.036GeAs2 (I), Cd0.964Zn0.036GeAs2:Mn (1.5 wt%) (II), and Cd0.964Zn0.036GeAs2:Mn (2.18 wt %) (III) retain the CdGeAs2 structure (tetragonal system, space group I\(\bar 4\)2d). The unit cell parameters of the solid solutions are as follows: a = b = 5.934(1) A, c = 11.219(2) A for I; a = b = 5.919(1) A, c = 11.204(2) A for II; and a = b = 5.918(1) A, c = 11.208(2) A for III. Many of Mn atoms in II and III occupy interstitial sites in the crystal lattice. Selected electrical and magnetic properties of single crystals of CdGeAs2:Mn(x) are discussed.

The magnetic-field dependences of the Hall coefficient and transverse magnetoresistance are studied experimentally and theoretically in p-Bi2Te3 crystals doped heavily with Sn and grown by the Czochralski method in the case of both classical and quantizing magnetic fields as high as 12 T with the magnetic-field orientation along the C 3 trigonal axis. The Shubnikov-de Haas effect and quantum oscillations of the Hall coefficient were measured at temperatures of 4.2 and 11 K. The six-ellipsoid Drabble-Wolfe model of the energy spectrum and the magnetic-field dependence of the Hall coefficient are used as the basis for the method for determining the Hall factor and Hall mobility. New evidence is obtained in support of the existence of the narrow band of impurity Sn states occupied partially with electrons against the background of the light-hole band spectrum. The parameters of impurity states are estimated including their energy (E Sn ≈ 15 meV), the broadening (Γ « kT), and the radius of localization of the impurity state (R ≈ 30 A).

InSb samples containing 0.22–1.42 wt % manganese were synthesized and identified. The unit cell parameter decreased as the manganese concentration increased. The samples contained microinclusions of manganese antimonides. Electrical and magnetic measurements showed two ferromagnetic phases (In1−xMnxSb solid solution with Tc ∼ 7 K and MnSb with Tc ∼ 580 K) and a ferrimagnetic phase (Mn2Sb). The samples had p-type conductivity with a charge carrier concentration of about 1020cm−3. The semiconductor conductivity was observed at low temperatures and changed to the metal conductivity with temperature elevation.

The Hall effect, electrical conductivity and electron mobility are investigated at temperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. The presence of a small amount of Cu atoms leads to an inversion of the sign of the Hall coefficient at temperatures above 300 K. Anomalous temperature dependence of the electron mobility is observed in the samples with low Cu concentration (

Magnetic properties of the group II–V semiconductor CdSb single crystals doped with Ni (2 at%) are investigated. Deviation of the zero-field-cooled susceptibility, χ ZFC , from the field-cooled susceptibility is observed below 300 K, along with a broad maximum of χ ZFC ( T ) at T b in fields below the anisotropy field B K ∼4 kG. T b ( B ) obeys the law [ T b ( B )/ T b (0)] 1/2 =1– B / B K with T b (0)∼100 K. The magnetization exhibits saturation above ∼20–30 kG, a weak temperature dependence and anisotropy of the saturation value M s . The coercive field is much smaller then B K and displays anisotropy inverted with respect to that of M s . Such magnetic behavior is expected for spheroidal Ni-rich Ni 1− x Sb x nanoparticles with high aspect ratio, broad distribution of the sizes and with orientations of the major axis distributed around a preferred direction.

The magnetic properties of oriented CdSb single crystals doped with 2 at% of Ni are investigated. From measurements of magnetic irreversibility defined by deviation of the zero-field-cooled (ZFC) susceptibility from the field-cooled (FC) susceptibility, the value of the mean anisotropy field BK ~ 4 kG is obtained. The ZFC susceptibility displays a broad maximum at a blocking temperature, Tb, depending on B according to the law [Tb(B)/Tb(0)]1/2 = 1 ? B/BK with Tb(0) ~ 100 K. The field dependence of the magnetization exhibits saturation above ~20?30 kG with values of Ms different for B along the [1?0?0], [0?1?0] and [0?0?1] axes. The temperature dependence of Ms is weak, increasing slightly upon cooling the sample below ~100 K. The temperature dependence of the coercive field, Bc(T), is weak above Tb but is enhanced strongly with decreasing temperature below Tb. The anisotropy of Bc is inverted with respect to the anisotropy of Ms. Such behaviour can be attributed to spheroidal Ni-rich Ni1?xSbx nanoparticles with a high aspect ratio, broad size distribution and distribution of the orientation of the major axis around a preferred direction. The relation Bc BK and the anisotropies of Ms and Bc are consistent with reversal of the magnetization by the curling mode, whereas the Tb(B) dependence is typical of the coherent rotation mode. This difference is connected to the proximity of the average transversal cluster radius to a critical value for transition between the two magnetization reversal modes within a wide crossover interval, due to broad distribution of the cluster sizes.

Magnetic susceptibility, χ ( T ) , is investigated in ceramic La 1− x Ba x MnO 3 (LBMO) with x = 0.02 – 0.25 in the range of fields B = 10 – 80 G and temperatures T = 5 – 310 K . All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with T C increasing with x from 177 K ( x = 0.02 ) to 295 K ( x = 0.25 ) and magnetic irreversibility decreasing below T C with increasing x . In the PM phase an interval of the Curie–Weiss behavior of χ ( T ) with an effective Bohr magneton number, p eff ∼ 30 – 40 , is observed above T 1 ∼ 260 – 290 K . Below T 1 and down to T cr ∼ 190 – 220 K the susceptibility follows the scaling law χ - 1 ( T ) - χ - 1 ( T C ) ∼ ( T / T C - 1 ) γ with γ = γ 1 ≈ 1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below T cr , χ ( T ) obeys the same scaling law as for T > T cr , but with another value of γ = γ 2 ≈ 1.7 – 1.8 , characteristic of a 3D percolation system. The temperature dependence of the susceptibility observed in the PM phase is explained by small FM particles embedded in the host LBMO matrix above T 1 . The size of these particles increases between T 1 and T cr up to nanometer scale, forming critical percolation clusters below T cr . The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.

The resistivity, ?, of ceramic La1?xBaxMnO3 with x = 0.02?0.10 corresponding to the concentrations of holes c?0.15?0.17 displays an activated behaviour both above and below the paramagnetic to ferromagnetic transition temperature TC = 175?209?K, obtained from measurements of the magnetization. Above T~310?390?K ?(T,x) is determined by nearest-neighbour hopping of small polarons with activation energy Ea = 0.20?0.22?eV. Below the onset temperature Tv = 250?280?K, depending on x, a Shklovskii?Efros-like variable-range hopping conductivity mechanism, governed by a soft temperature independent Coulomb gap, ??0.44?0.46?eV, and a rigid gap, ?(T), is found. For the range T~50?120?K, ?(T) is connected to the formation of small lattice polarons in conditions of strong electron?phonon interaction and lattice disorder. The rigid gap obeys a law ?(T)~T1/2 within two temperature intervals above and below TC, exhibits an inflection at TC and reaches at Tv a value of ?v?0.14?0.18?eV. Such behaviour suggests a spin dependent contribution to ?(T). The localization radius of the charge carriers, a, has different constant values within the temperature intervals where ?(T)~T1/2. With further decrease of T, a increases according to the law expected for small lattice polarons.

Structural and transport properties of ceramic LaMnO3+δ are investigated for δ = 0–0.154. According to x-ray diffraction measurements at room temperature the crystal structure of this compound varies from orthorhombic (Pbnm )f orδ = 0t or hombohedrally distorted cubic (Pm3m )f or δ = 0.065–0.112 and to rhombohedral (R ¯ 3c )c rystal symmetry for δ = 0.125–0.154. These structural modifications are confirmed by the Raman micro-spectroscopy measurements. The resistivity displays in the range δ = 0–0.154 an activated behaviour both above and below the paramagnetic (PM) to ferromagnetic transition temperature, TC .I n the f ieldof 8 T the relative magnetoresistance, �ρ( B)/ρ(0) ,r eaches at δ = 0.154 the values of −88% near TC and −98% at T ≈ 20 K. The resistivity of the PM phase of LaMnO3+δ with δ = 0.100–0.154 satisfies the Shklovskii–Efros-like variablerange hopping (VRH) conductivity law between TC ∼ 130–160 K and the VRH onset temperature Tv ∼ 250–270 K. The resistivity is governed by a complex energy dependence of the density of the localized states near the Fermi level, comprising a soft Coulomb gap � ≈ 0.43–0.48 eV and a rigid gap γ ≈ 0.14–0.17 eV, the latter being connected to formation of small polarons. (Some figures in this article are in colour only in the electronic version)

Reliable correlation of simultaneously measured resistively, susceptibility and specific heat critical parameters of hole-underdoped YBCO permitted to establish a phenomenological model of normal-superconductor transition. After the model, fluctuations of quasifree electrons drives at T * ≫ T C the appearance of paired charge carriers (pseudogap-PG) characterized by partial coherence of the order parameter’s phase. The evolution of PG state from T * ∼ 140 K to the critical temperature T C ∼ 92 K is connected to the average increase of the statistically distributed partial coherence lifetime (from τ ∼ ps to ∞) and coherence length (from λ ∼ nm to ∞) of the fluctuating precursor islands. In this dynamic process the specific heat’s maximum signals (at temperature T CC ∼ 93.6 K) the appearance of the first mesoscopic coherent islands. T C marks the percolation of these islands. We believe that the presented concept of dynamical evolution (in coherence time and space from 0 to ∞) of the paired charge structures is a promising scenario while describing the properties of hole doped high- T C superconductors between the temperatures T * and T C .

Simultaneous ac magnetic susceptibility and specific heat studies of YBCO ceramics permitted the correct correlation of the corresponding critical temperatures. The midpoint of the real component (χ′) and the maximum of the imaginary component (χ′′) of ac susceptibility curves confirmed the T c = 92 K critical temperature value determined by dc resistance measurements. The specific heat maximum's temperature (T cc ∼ 93.6 K)—-taken as the calorimetric critical one—fell between T c and T* (the pseudogap onset temperature). We suggest that T cc signals the appearance of the first localized coherent pairs, while the temperature T c marks their percolation. The existence of two different critical temperature values confirms the coexistence of partial coherent and coherent electron pairing phenomena in the region below T cc of the superconducting phase diagram.

The Hall effect in the anisotropic II–V group semiconductor p-CdSb is investigated at temperatures between T = 3.6 and 200 K and pulsed magnetic fields up to B = 25 T in unintentionally doped samples oriented along the crystallographic axes [100] and [010]. The Hall coefficient, R(B, T), with B ∥ [001] exhibits in low fields a flat region followed by a descending interval when B is increased. This behaviour is attributed to the presence of two groups of holes with concentrations p2(T) > p1(T) and mobilities μ2(T) Tcr p1 and p2 are related to the holes activated to the light- and heavy-hole bands, respectively. The analysis of μ1(T) and μ2(T) confirms the existence of the heavy-hole band or a non-equivalent maximum and two equivalent maxima of the light-hole valence band.

The resistivity of the anisotropic semiconductor p-CdSb is investigated in a wide temperature range of T = 1.9–300 K in pulsed magnetic fields up to B = 25 T. Two not intentionally doped single-crystalline samples oriented along the crystallographic axes [100] (no. 1) and [010] (no. 2) are used for measurements of the resistivity, ρ, in transversal magnetic field configuration. Below the resistivity follows the laws for B Bc, where the coefficients C and S do not depend on T, and . These are characteristics of nearest-neighbour hopping conductivity. The coefficients C and S depend on the direction of B, and their ratios agree completely with the values calculated with the components of the hole effective mass. The acceptor concentrations, and for no. 1 and no. 2, respectively, are relatively close to the critical value of the metal–insulator transition (MIT), . This leads to enhancement of the mean localization radii, in no. 1 and in no. 2, with respect to the value of far from the MIT determined by an asymptote of the wavefunction at a large distance from the impurity centre.

In a weak (B=2 G ) magnetic field LaMnO3+δ exhibits at δ=0.065 below the paramagnetic-to-ferromagnetic (FM) Curie temperature, TC, a mixed (spin-glass and FM) phase followed by a frustrated FM phase at δ between 0.100 and 0.154. The same behavior is observed in La1−xCaxMnO3 with x between 0 and 0.3. This can be understood by the similar variation of the Mn4+ concentration, c between ≈0.13 and 0.34, in both materials when x or δ is increased. On the other hand, considerable differences are found between these compounds in the values of the magnetic irreversibility, in the dependencies of TC(c) and the magnetic susceptibility, χ(c), as well as in the critical behavior of χ(T) near TC. These differences can be explained by distortions of the cubic perovskite structure, by the reduced lattice disorder and by the more homogeneous hole distribution in LaMnO3+δ than in La1−xCaxMnO3.

The effects of the temperature gradient ( p ) and heat transfer’s velocity ( q ) parameters on the shape of AC susceptibility curves were experimentally explored. At homogeneous Y 1.01 Ba 1.95 Cu 2.97 O 6.86 ceramic samples only broadening with negligible horizontal translation and shape distortions of the χ ′ and χ ″ susceptibility curves were observed. At samples with local inhomogeneity—beside broadening—a proportional peak-deep-hump type distortion and horizontal translation of the χ ″, and rotational translation of the χ ′ curves appeared. The results—leading to a clearer understanding of how inhomogeneities and the scanning parameters influence the shape of the AC susceptibility curves—allow separating the effects of local inhomogeneities from the ones produced by structural modifications. It is confirmed that the spatial resolution of the method for local inhomogeneities is proportional to p and inversely proportional to q until a limit is determined mainly by the relaxation time of the studied phenomenon.

Low-field (B=2−80 G ) dc magnetic susceptibility, χ, investigated in hole-doped La1−xCaxMn1−yFeyO3 (LCMFO) with x=0.3 and y=0.05−0.10, exhibits non-uniform critical behavior near the paramagnetic (PM)-to-ferromagnetic (FM) transition temperature, TC. We observe the scaling law, χ−1(T)−χ−1(TC)∼(T/TC−1)γ≡τγ, with γ≈1.4 corresponding to a 3D Heisenberg spin system below τcr∼0.1–0.2, and with γ≈1.7 characterizing a 3D percolation system, above τcr. The non-universal scaling results from strongly inhomogeneous distribution of holes leading to formation of percolation clusters from the hole-rich nanoscale FM particles, embedded in the host PM matrix. The resistivity, ρ, of LCMFO exhibits between a temperature T v ≈310–330 K and TC the Shklovskii–Efros-type variable-range hopping conductivity law, ρ(T)=ρ0(T)exp[(T0/T)1/2], governed by generation of a complex gap in the density of states. The prefactor follows the law ρ0(T)∼Tm, where m changes from 9/2 at y=0 to 5/2 at y=0.03, 0.07 and 0.09, reflecting an additional fluctuating short-range potential induced by doping with Fe.

Thermopower and conductivity are measured for the perovskite-like manganite La1−xBaxMnO3 (0.02⩽x⩽0.35) in the temperature range 200–950°C and oxygen pressure varying between 10−11 and 0.5 atm. The data for thermopower and electrical conductivity indicate a transport mechanism dominated by adiabatic hopes of small polarons. The high-temperature limit for the thermopower is mainly defined by the spin contribution while configurational contribution does not depend essentially on the doping level. Changes in the conductivity with doping are shown to reflect variations in the mobility of charge carriers.

The ac response of a slab of a clean type-II superconductor in the mixed state is theoretically investigated taking into account the bulk and surface pinning. In extremely clean superconductors sharp resonances of the ac response are predicted. Pinning-induced resonance is found only for an asymmetric ac magnetic field h(ω) pattern with the direction of h(ω) being opposite on opposite sides of the superconducting slab. The contribution of the surface pinning to the resonance frequency depends on the tilt modulus of the flux line lattice. A resonance at the cyclotronic frequency is found only in samples thinner than the London penetration depth. In the universal flux-flow regime, predicted for d-wave superconductors, wide maxima are found in the frequency dependence of the ac absorption.

A narrow dip is observed around zero magnetic field in magnetization curves M(B) of superconducting YBCO films with about 10 nm thickness. This anomaly occurs in the same field range with an anomaly of ac surface impedance Z(B) found recently in thin YBCO films. Because the thickness of our films is considerably less than the London penetration depth, two-dimensional limit of the critical state model is applied. In the framework of this model the magnetic field dependence of the critical current density jc(B) is found. The obtained jc(B) function agrees well with that found in the ac surface impedance investigation.

Low-field ( B =2–80 G) DC magnetic susceptibility, χ , is investigated in ceramic La 1− x Ca x Mn 1− y Fe y O 3 (LCMFO) samples with x =0.3. When y is increased from 0 to 0.1 the ferromagnetic (FM) Curie temperature, T C , decreases from 259 to 107 K, indicating growth of disorder by iron doping. A transformation of LCMFO from a weakly frustrated FM phase between y ≈0–0.05 to a strongly frustrated mixed, FM and glassy, phase between y ≈0.07–0.10 is revealed by measurements of magnetic irreversibility and long-time (up to t =10 5 s) relaxation of thermoremanent magnetization. Critical behavior of χ ( T ) obeying the scaling law χ −1 ( T )− χ −1 ( T C )∼( T / T C −1) γ ≡ τ γ is observed below τ cr ∼0.05–0.2 with γ = γ 1 ≈1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Above τ cr , χ ( T ) can be fitted with the same scaling law as for τ τ cr , but with another value of γ = γ 2 ≈1.7, which characterizes a 3D percolation system. The change of γ upon lowering the temperature can be explained by the formation of percolation clusters from an assembly of hole-rich nanoscale particles of the second FM phase embedded into the host LCMFO matrix at T well above T C . The magnetic moments, radii, and concentration of these particles are determined.

The resistivity, ρ, of ceramic La1−xCaxMn1−yFeyO3 with x = 0.3 and y = 0.0–0.09 is found to obey, between a temperature Tv ≈ 310–330 K and the ferromagnetic-to-paramagnetic transition temperature, TC = 259–119 K (decreasing with y), the Shklovskii–Efros-type variable-range hopping conductivity law, ρ(T) = ρ0 (T) exp [(T0 /T)1/2 ]. This behaviour is governed by generation of a soft Coulomb gap Δ ≈ 0.42 eV in the density of localized states and a rigid gap δ(T) ≈ δ(Tv)(T/Tv)1/2 with δ(Tv) ≈ 0.16, 0.13 and 0.12 eV at y = 0.03, 0.07 and 0.09, respectively. Deviations from the square root dependence of δ(T), decreasing when y is increased, are observed as T → TC. The prefactor of the resistivity follows the law ρ0 (T) ~ Tm, where m changes from 9/2 at y = 0 to 5/2 in the investigated samples with y = 0.03, 0.07 and 0.09, which is connected to introduction of an additional fluctuating short-range potential by doping with Fe.

Using a variant of the AC susceptibility method, we have demonstrated that under non-equilibrium thermal conditions, spontaneous incoherent local diamagnetic fluctuations could lead to large coherent oscillatory relaxation in YBCO ceramics above Tc. The probability and the amplitude of giant relaxation become maximum at ∼50% volume fraction of the diamagnetic state. Using the size of the largest synchronous cluster (determined from the amplitude of susceptibility relaxation) as coherence length (ξ VG ∼1.6±0.1 mm ) together with the directly measured repetition period of the relaxation (τ∼10±1 s ), the critical dynamic exponent has been calculated to be z=4.9±1. This value is in agreement with published vortex-glass exponent data.

A high number of normal-superconductor transitions of sintered YBCO samples have been monitored by AC susceptibility measurements simultaneously in three different regions of samples, in the presence of strong thermal gradient. With this method, different accidental mesoscopic vortex structure instabilities have not only been observed but also located. Even if local magnetothermal instabilities of oscillatory nature (f=0.1–0.02 Hz ) appear in strong thermal gradient fields, their evolution remains localized. However, when such instabilities appear in superposed temperature and electric (DC) potential gradient fields, they travel together with the mixed-state zone (v=0.06–0.1 mm s −1 ) along the macroscopic specimen. The interaction of transport currents with shielding current instabilities of the mixed-state — modifying some percolative network paths — can be considered as a possible macroscopic scenario for the traveling instabilities.

Effects of deformation of flux lines on electrodynamics is investigated near the surface of a type-II superconductor in the mixed state when dc magnetic field is perpendicular to the surface. One- and two-mode approximations to the problem are presented. It is shown that the surface effects can be described by an effective boundary condition for a dense flux line lattice ( B ≫ H c1 , where H c1 is the lower critical field) in the two-mode approximation. This condition determines the relative value of the amplitudes of the modes.

A change in the electrical conductivity, σ, is observed in the manganese perovskite La1−x CaxMnO3, with x=0 and 0.3 under saturation of the magnetic resonance transitions of Mn ions. This effect has a maximum in the temperature range of the magnetic phase transition of the compounds. Two contributions to the change in σ are found. The first, dominating in LaMnO3, is an increase in σ caused by heating of the sample under magnetic resonance. The second is a σ decrease due to reorientation of the Mn spins, observed in La0.7Ca0.3MnO3.

In ceramic La1-xCaxMnO3 samples with 0≤x≤0.15 and the concentration of holes c = 0.18-0.22 between T = 77 and 340 K the resistivity, ρ, is shown to have an activated character both above and below the ferromagnetic Curie temperature, TC. The temperature dependence of the local activation energy, Eloc (T) = dln ρ(T)/d(kT)-1 gives evidence for a variable-range hopping conductivity over states of the Coulomb gap. The width of the gap Δ≈0.24 eV, the effective dielectric permeability κ≈3.6 and the carrier localization radius ξ≈5.1 A in the paramagnetic phase are determined. The value of ξ suggests hopping of small lattice polarons at T>TC. With decreasing temperature two successive transitions, at temperatures TC' and TC'', associated with divergence of the correlation length, are observed in the vicinity of TC. They can be interpreted in terms of critical increase (as T approaches TC' from higher temperatures) and decrease (when T shifts from TC'' towards lower temperatures) of the radius of magnetic polarons, generated by a small fraction of the lattice polarons as T→TC. The difference between TC and the temperature of the first divergence of ξ, TC'

AC susceptibility has been measured simultaneously in three different regions of YBCO ceramic samples, in the presence of a strong thermal gradient, in order to pinpoint local perturbation. A local step-like perturbation, applied in addition to the monotonic temperature decrease, produces a jump-like increase of the coherent region. The superconducting regions enlarge much faster than the propagation of the thermal waves. We suggest that the adiabatic magnetic flux jump reflect the creation of new coherent domains over Tc by stimulated correlation of the order parameter phase.

The re-entrant state in the Pd 11 Co 50 Al 39 alloy is investigated by dc and ac magnetization measurements. A dynamic scaling analysis of ac susceptibility data indicates a true spin-glass state below 5.6 K. Magnetic aging, characteristic of spin-glass dynamics, persists well into the re-entrant ferromagnetic phase of Pd 11 Co 50 Al 39 . Borders of the re-entrant spin-glass and ferromagnetic behaviour are established for this allov.

Low-field magnetic properties of ceramic La1-xCaxMnO3 (0≤x≤0.4) are investigated between T = 5 and 310 K. The paramagnetic-ferromagnetic transition is observed in all the samples. The dependence of the Curie temperature, TC, on x is described within a model of spin polarons associated with electronic localization. Critical behaviour of the susceptibility χ-1(T ) ~ (T-TC)γ is observed for T>TC, with the critical exponents γ = 1.20±0.05 and γ* = 1.64±0.06 below and above the composition x≈0.18 corresponding to the Mn4+ ion concentration c ≈ 0.23, respectively. For the compound with x = 0.3 no temperature hysteresis of the resistivity is observed in magnetic fields between 0 and 8 T. In all the samples the field-cooled and zero-field-cooled magnetizations deviate below TC, the difference being approximately equal to the thermoremanent magnetization (TRM). Long-time relaxation of TRM in LCMO is observed for time scales up to 104 s. The relaxation rate reaches a maximum near a wait time tW ~ 103 s. The time dependence of TRM can be described with a stretched exponential law, as in spin or cluster glasses in conditions where the observation time is comparable with tW .

Magnetic relaxation measurements are made in the remanent state of pure and Zn-doped submicron YBCO powders. A characteristic feature of these samples is dipolar interaction between single vortices trapped in different particles. Similar to other systems with dipolar interactions, such as powders of fine ferromagnetic particles, our samples show glassy behaviour: different metastable states with various pinning properties can be prepared by varying the strength of the magnetizing field, i.e. history of the sample. It is found also that the relation between the pinning energy and the magnetic moment can be described by an expression similar to the vortex glass interpolation formula.

Magnetic properties of cubic La 1− x Ca x MnO 3 (0⩽ x ⩽0.4) are investigated between T =5 and 310 K in the external field of 2 G. The dependence of the ferromagnetic transition temperature on x is analyzed with the model of spin polarons associated with electronic localization and electron–electron interaction. The bandwidth of the localized electrons is found to be W =1.90±0.05 eV. In the samples with x 4+ concentration c T 1 , on c can be well described by a model including the Mn 3+ –Mn 3+ superexchange and the Mn 3+ –Mn 4+ double-exchange interactions. In the samples with x ⩽0.2 and c ⩽0.22 the value of the critical exponent, γ =1.21±0.05, is obtained for the temperature dependence of the zero-field-cooled susceptibility function χ −1 ( T )∼( T − T C ) γ , for T > T C .

We describe a new experimental technique where ac susceptibility is measured simultaneously with three pick-up coils in three different regions along a YBCO ceramic sample, in the presence of strong thermal gradient. Each of the pick-up coils “feels” the shielding currents from the entire sample but with different weight due to geometrical factors. The multiple coil system permits the localization of any particularities (here a local avalanche-like decrease of the susceptibility function). Using this technique we observed experimental evidence of adiabatic flux change in a sintered high Tc superconductive material.

To compare superconducting transitions under slow and fast altered temperature gradients the ac susceptibility was measured simultaneously in three different regions of Y-Ba-Cu-O ceramic samples. The flux dynamics of a Y-Ba-Cu-O sample either exposed or not to a slowly varying temperature gradient remain the same (conventional behaviour). The flux dynamics of the same sample exposed to a quickly varying temperature gradient (v >0.32Ks−1) are qualitatively different. During fast cooling (or heating) the start (or the end) of the flux expulsion (or admission) in the first region of the increasing state stimulates the beginning (or the end) of the flux expulsion (or admission) in the regions of the following decreasing state. Consequently in some regions the transition of the decreasing state begins (terminates) prematurely well over (under) the conventional onset temperature of the sample. Thus, during cooling, overheated superconducting regions and, during heating, undercooled normal macroscopic r...

Magnetic properties of the II-V diluted magnetic semiconductor .Zn1 x Mnx/3As2 are investigated for xD 0:08, 0.10 and 0.13, betweenT D 3 and 500 K and in fields up to 60 kG. All samples show a steep decrease of the magnetization above 280 K. In low fields (5-80 G) the temperature dependence of the magnetic susceptibility is strongly irreversible below the blocking temperatureTb 250 K. Above 15 kG the difference between the zero-field-cooled and the field- cooled susceptibilities disappears. These features give evidence for the presence of two magnetic subsystems: (i) paramagnetic centres including a single Mn ion and an open or closed triple antiferromagnetic cluster of Mn 2+ and (ii) ferromagnetic MnAs nanoclusters. The size distribution of the MnAs clusters is described by two overlapping Gaussian functions with the maxima at R1D 2:6-3.1 nm andR2D 3:3-3.8 nm, depending onx.