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A large range of nanoscale superparamagnetic materials has been under scrutiny from the point of view of their potential theranostic, multimodal applications. In this paper we have investigated the effect of replacing Fe3+ cations with Gd3+ and Tb3+ in the core of the superparamagnetic iron oxide nanoparticles in search for the optimum level of magnetic core doping with these lanthanides. We have found that the presence of Gd3+ and Tb3+ up to 2.5% at. does not alter significantly the crystallographic structure of such nanoferrites and does not compromise the magnetic properties of doped nanoparticles. The doping level, though relatively small, exceeds the levels of currently used radiopharmaceuticals, where only few radionuclides can be incorporated in a single radiotherapeutic molecule. This new type of multifunctional nanoparticles can be used not only as drug carriers or in magnetic hyperthermia, but also in the so-called endoradiotherapy. The latter feature can be easily implemented upon the replacement of “cold” ions of Tb3+ and Gd3+ in the superparamagnetic core with their isotopes emitting soft β− radiation suitable for the internal radiotherapy, localized directly within the tumor. Therefore, these nanoparticles can be used simultaneously in targeted drug delivery, hyperthermia and radiotherapy.

The Griffiths phase in fine grain manganite La0.75Ca0.25MnO3 is studied by the complementary structural methods, DC magnetic susceptibility and ESR spectroscopy. The Griffiths like phase is detected above Curie temperature between 232 and 280 K and sustains up to high magnetic field of 3000 Oe. The magnetic susceptibility of Griffiths phase is a decreasing function of temperature. The magnetic field dependence of Griffiths phase susceptibility reveals its remarkable contribution to measured total susceptibility. The additional anomalous ESR signal supperimpossed on the paramagnetic one is ascribed to the locally inhomogeneous Griffiths like phase in agreement with the core – shell model.

In this paper, we study the effect of the signal-to-noise ratio of magnetization measurements on the determination of the Curie temperature from the analysis of the magnetocaloric response. The procedure has been compared with the method of the inflection point of the magnetization versus temperature curves. Magnetization data have been simulated using the Arrott–Noakes equation of state, with the addition of different noise levels (either 1% of the measured signal or 0.3% of the measurement range). It is shown that the obtained values of the Curie temperature are more accurate in the case of the magnetocaloric procedure, although this method requires more data analysis than the inflection point method. Moreover, the field independence of the Curie temperature obtained from the magnetocaloric procedure allows us to perform a statistical analysis of the obtained values, reducing the associated error in the Curie temperature determination.

A systematic investigation on the structural, magnetic and magnetocaloric properties of Pr 0.6 Sr 0.4– x Ag x MnO 3 ( x =0.05 and 0.1) manganites was reported. Rietveld refinements of the X-ray diffraction patterns confirmed that all samples were single phase and crystallized in the orthorhombic structure with Pnma space group. Magnetic measurements in a magnetic applied field of 0.01 T revealed that the ferromagnetic-paramagnetic transition temperature T C decreased from about 293 to 290 K with increasing silver content from x =0.05 to 0.1. The reported magnetocaloric entropy change and relative cooling power for both samples were considerably remarkable with a Δ S max value of 1.9 J/(kg·K) and maximum RCP values of 100 J/kg, under a magnetic field change (Δ µ 0 H ) equal to 1.8 T. The analysis of the universal curves gave an evidence of a second order magnetic transition for the studied samples. The magnetic field influence on both the magnetic entropy change and the relative cooling power was also studied and discussed.

The influence of Co content on the structural and hard magnetic properties of two sets of nanocrystalline Fe 52−x Co x Pt 28 B 20 (x = 0–26) and Fe 60−y Co y Pt 25 B 15 (y = 0–40) alloys was studied. The alloys were prepared as ribbons by the rapid quenching technique. The nanocomposite structure in the alloys was obtained by annealing at 840–880 K for 30 min. Structural characterization of the samples was performed using the Mossbauer spectroscopy and X-ray diffraction. Magnetic properties of the samples were studied by the measurements of the hysteresis loops and of the magnetization at increasing temperatures. An amorphous phase prevailed in the as-quenched Fe 52−x Co x Pt 28 B 20 alloys while a disordered solid solution of fcc-(Fe,Co)Pt was a dominating phase in the Fe 60−y Co y Pt 25 B 15 ribbons. Differential scanning calorimetry measurements revealed one or two exothermic peaks at temperatures up to 993 K, depending on the composition of the alloys. Thermal treatment of the samples led to the formation of the magnetically hard ordered L1 0 tetragonal (Fe,Co)Pt nanocrystallites and magnetically softer phases of (Fe,Co)B (for Fe 52−x Co x Pt 28 B 20 ) or (Fe,Co) 2 B (for Fe 60−y Co y Pt 25 B 15 ). Detailed Mossbauer spectroscopy studies revealed that cobalt substituted for iron in both the L1 0 phase and in iron borides. The nanocomposite Fe 60−y Co y Pt 25 B 15 alloys exhibited significantly larger magnetic remanence and maximum energy products but a smaller coercivity than those observed for the Fe 52−x Co x Pt 28 B 20 alloys. Co addition caused a reduction of the magnetization and the energy product in both series of the alloys. The largest magnetic remanence of 0.87 T and the highest energy product (BH) max = 80 kJ/m 3 were obtained for the Co-free Fe 52 Pt 28 B 20 alloy while the largest coercivity (H C > 950 kA/m) was observed for the Fe 50 Co 10 Pt 25 B 15 and Fe 30 Co 30 Pt 25 B 15 alloys. Differences in the hard magnetic properties of the nanocomposite alloys were related to different phase compositions influencing the strength of inter-phase exchange coupling interactions.

The magnetocaloric effect in the vicinity of the martensitic transformation for a single crystalline alloy with a composition close to the stoichiometric Ni2MnGa 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.

Iron oxide-based nanoparticles have been modified in their core with holmium(III) in an amount affecting only slightly their magnetic properties. Nanoparticles were conjugated covalently with biomolecule of trastuzumab (Herceptin&reg, ), the monoclonal antibody that recognizes cancer cells overexpressing HER2 receptors targeting such nanoparticles to the specified tumor tissues. Systematic studies of Ho3+-doped bioconjugates were carried out as a preliminary step for future replacement of &lsquo, cold&rsquo, Ho with 166Ho radionuclide, emitting &lsquo, soft&rsquo, beta(-) radiation for possible targeted radionuclide therapy. Physicochemical properties of the obtained bioconjugates were subsequently tested for use in magnetic hyperthermia, considered as an effective, low-invasiveness anticancer therapy. With such a system we expect to achieve both: active targeting and multimodal action by simultaneous internal and localized irradiation and magnetic hyperthermia of specific cancers.

The Griffiths like phase embedded into paramagnetic matrix of mixed valence orthorhombic nanocrystalline manganite La0.50Ca0.50MnO3 is experimentally studied by means of sensitive magnetic susceptibility and electron spin resonance. A comparative study of the nano- and polycrystalline manganites indicates the temperature interval of the Griffiths like phase located above the Curie temperature of nanocrystalline one. The upper temperature limit for an existence of Griffiths like phase, revealed by the sensitive electron spin resonance, is 10 K higher than that of the magnetic susceptibility. This proves that the high frequency field is able to excite the relatively smaller magnetic clusters.

The critical properties of monovalent doped manganite Pr 0.55 K 0.05 Sr 0.4 MnO 3 around the paramagnetic to ferromagnetic phase transition were investigated through various methods: the modified Arrott plots (MAP), the Kouvel–Fisher method and the critical isotherm analysis. Data obtained near T c were examined in the framework of the mean field theory, the 3D-Heisenberg model, the 3D-Ising model, and tricritical mean field. The deduced critical exponents values obtained using MAP method were found to be β =0.44(4) with T C ≈303 K and γ =1.04(1) with T C ≈302 K. Kouvel–Fisher method supplies the critical values to be β =0.41(2) with T C ≈302 K and γ =1.09(1) with T C ≈302 K. The obtained critical parameters show a tendency towards the mean-field behavior, suggesting the existence of long-range ferromagnetic order in the compound studied. The exponent δ deduced separately from isotherm analysis at T =303 K was found to obey to the Widom scaling relation δ =1+ γ / β . The reliability of obtained exponents was confirmed by using the universal scaling hypothesis. The itinerant character of ferromagnetism in the present system was also tested by using Rhodes–Wohlfarth's criterion.

This comment compares the temperature extent of the Griffiths like phase in delafossite compound CuCr0.95Ti0.05O2 as determined by two different methods. It is shown that the λ – TCR method underestimates a temperature extent of Griffiths phase. Finally it is argued that the temperature location of Griffiths phase should be determined by the more sensitive differential method instead of the λ – TCR method.

We have investigated the effect of gadolinium doping on the structural and electrical properties of Pr0.5−x Gd x Sr0.5MnO3(x=0.0−0.1) manganites. Our samples have been elaborated using the solid-state reaction, at high temperature. Rietveld refinement of the X-ray diffraction patterns has shown that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Scanning electron microscopy (SEM) revealed that the grains are irregularly spherical-like shaped with mean sizes of 380, 450, and 460 nm for x=0,0.05, and 0.1, respectively. Increasing Gd content enhances electrical resistivity values. Extrinsic magnetoresistance is observed at low temperature.

Poly- and nanocrystalline manganite composites (1/3)La0.7Ca0.3MnO3/(2/3)La0.8Sr0.2MnO3 prepared by the sol–gel method are studied by magnetic and transport measurements. The Arrott plots and universal curve of magnetic entropy change confirm that magnetic transition is of the second order. The magnetocaloric effect of polycrystalline composite is found to be roughly twice smaller as compared to the polycrystalline Ca- and Sr-based parent phases. The nanocrystalline composite of the same composition exhibits only 8% reduction of magnetic entropy change. Due to the large temperature spread of magnetocaloric effect the relative cooling power RCP of nanocrystalline composite is about three times larger as compared to the nanocrystalline Ca- and Sr-based parent phases. The maximum magnetic entropy change DSMAX and relative cooling power RCP are found to be more sensitive to magnetic field strength for the nano- than for polycrystalline composites studied.

Pr 0.55 K 0.05 Sr 0.4 MnO 3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with P nma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000–1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic–ferromagnetic transition at the Curie temperature T C = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg − 1 K −1 , resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013).

Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition.

The monovalent potassium doped manganites Pr 0.6 Sr 0.4− x K x MnO 3 ( x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature.

An orthorhombic DyMnO 3 single crystal has been studied in magnetic fields up to 14 T and between 3 Kand room temperature. The field dependent ordering temperature of Dy moments is deduced. Theparamagnetic Curie Weiss behavior is related mainly to the Dy 3þ sublattice whereas the Mn sublatticecontribution plays a secondary role. DC magnetization measurements show marked anisotropicfeatures, related to the anisotropic structure of a cubic system stretched along a body diagonal, witha magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin floptransition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome bymagnetic fields up to 1.6 T.& 2013 Elsevier B.V. All rights reserved. 1. IntroductionManganites are manganese compounds of composition AMnO 3 ,where e.g. A¼ La, Ca, Ba,y, which crystallize in the cubic structureof the so called ‘‘perovskite mineral’’ CaTiO 3 . Depending on thecomposition they show a wide variety of magnetic and electricphenomena, including ferromagnetic, antiferromagnetic, chargeand orbital ordering. The multiferroic behavior and magnetoresis-tive effects make such oxides as natural candidates for potentialspintronics applications [1,2]. Intrinsic anisotropy is induced if theA site is occupied by different types of ions, with e.g. differentintrinsic charges. When the site A is partially or fully occupied by amagnetic ion, a severe intrinsic anistropy may be induced and thecompounds show different anisotropic behaviors as the tempera-ture is changed. This is considerable if the A ion has an f-shell, likein the rare earth ions. It is easily guessed that such anisotropicfeatures will surely depend on the orientation of any appliedmagnetic field.The perovskites manganites where A is a rare-earth (RE)element present the coexistence of magnetism and ferroelectricity.Moreover, either orthorhombic or hexagonal REMnO

The manganite Pr0.55Na0.05Sr0.4MnO3 prepared by solid state reaction has the orthorhombic structure and mean crystallite size of 51 nm. Scanning electron microscopy (SEM) shows that the grains are irregularly spherical like shaped with sizes 400 to 700 nm. In vicinity of Curie temperature equal to 289 K the magnetic entropy change |ΔSMmax| attains 1.75 J kg−1 K−1 under an applied magnetic field of 2 T which corresponds to relative cooling power of 93 J/kg. Electrical resistivity measurements reveal a transition from metallic to semiconductor phase. Temperature variation of electrical resistivity was fitted by the small polaron hopping (SPH) and Mott’s Variable range Hopping (VRH) models. The activation energy and Mott temperature are found to decrease and N(EF) to increase in magnetic field varying from zero to 1 T. The phonon contribution dominates in thermal conductivity.

A systematic investigation of structural, magnetic, and magnetocaloric properties is reported for a series of monovalent sodium-doped manganites Pr0.6Sr0.4−x Na x MnO3 (x = 0, 0.05, 0.1, 0.15, and 0.2). Rietveld refinements of the X-ray diffraction patterns show that all powder samples are single-phased and crystallized in the orthorhombic structure with Pnma space group. Magnetic characterization and Arrott plot confirm the second-order phase transition at Curie temperature T C decreasing from 310 K for x = 0 down to 272 K for x = 0.2. Magnetic entropy change is largest for x = 0 reaching 1.95 J kg−1 K−1 at 2 T field. This corresponds to a large relative cooling power of 102 J kg−1 . Magnetic field sensitivity of magnetic entropy change and relative cooling power are analyzed and discussed.

Hybrid materials consisting of a monoolein lipidic cubic phase (LCP) incorporating two types of magnetic nanoparticles (NP) were designed as addressable drug delivery systems. The materials, prepared in the form of a gel, were subsequently used as a macroscopic layer modifying an electrode and, after dispersion to nanoscale, as magnetocubosomes. These two LCPs were characterized by small-angle X-ray scattering (SAXS), cross-polarized microscopy, magnetic measurements, and phase diagrams. The magnetic dopants were hydrophobic NPoleic and hydrophilic NPcitric, characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and their influence on the properties of the cubic phases was investigated. The removal of the anticancer drug, Doxorubicin (Dox) from the hybrid cubic phase gels was studied by electrochemical methods. The advantages of incorporating magnetic nanoparticles into the self-assembled lipid liquid crystalline phases include the ability to address the cubic phase na...

The electrical resistivity in the mixed state of Bi2212 tape superconductors can be accurately reconstructed for values below approximately a half of the normal state value of resistivity, assuming a Gaussian distribution for the vortex lattice melting temperatures. The magnetic field dependences of the distribution width and of the dBc2/dT parameter were calculated. Moreover the vortex liquid viscosity coefficient was determined between the vortex lattice melting temperature and Tc at various magnetic fields. It is pointed out that the vortex lattice melting transition should not be confused with the irreversibility line of magnetic studies nor with the percolation temperature line for electrical resistivity. © 1998 Elsevier Science B.V. All rights reserved.

Single-phased nanocrystalline particles of pure and 10 % Ti 4+-doped perovskite-related YFeO 3were prepared via mechanosynthesis at 450∘C. This temperature is ∼150–350 ∘C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti 4+ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe 3+ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti 4+ lowers the Neel temperature of the YFeO 3 nanoparticles from ∼ 586 K to ∼ 521 K. The Ti 4+-doped YFeO 3 nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The 57Fe Mossbauer spectra show ∼ 15 % of the YFeO 3 nanoparticles and ∼22 of Ti 4+-doped YFeO 3 ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the 57Fe Mossbauer spectra suggest size-dependent hyperfine magnetic fields at the 57Fe nuclear sites and were associated with collective magnetic excitations. The 57Fe Mossbauer spectra show the local environments of the Fe 3+ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti 4+ ions relative to those in the larger magnetic nanoparticles.

Structural and electrical properties of the mixed-valence monovalent doped manganites Pr0.6Sr0.4−x K x MnO3 (x=0, 0.05 and 0.1), prepared using the conventional solid-state synthesis method, have been investigated. Rietveld refinement of the X-ray diffraction patterns at room temperature shows a slight increase in unit cell volume with K content and confirms that all powder samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Electrical resistivity measurements under and without magnetic field show a transition from the metallic to insulating behavior. The electrical conductivity is improved with increasing K content. The resistivity data in metallic region were fitted according to the electron–electron scattering process while in insulating region they were fitted using the small polaron hopping SPH model and Mott’s variable range hopping VRH model.

The mechanosynthesis of Fe 50 Zn 50 alloy resulted in the formation of the bcc Fe(Zn) solid solution after 20 h of milling. Structural transformations induced by mechanical alloying and heating, and magnetic properties of the powders were studied by Mossbauer spectroscopy, X-ray diffraction, Faraday balance and vibrating sample magnetometry techniques. All alloys studied exhibit strong magnetic ordering with Curie temperatures close to 900 K. Room temperature Mossbauer measurements revealed distinguished magnetic environments in the samples. The decrease of coercivity with prolonged milling time was attributed to the reduction or averaging of local magnetic anisotropies.

The orthorhombic Sr-doped manganite Pr 0.6 Sr 0.35 Na 0.05 MnO 3 synthesized using the conventional solid state reaction at high temperature is characterized by magnetic and electron transport studies. Structural data shows that crystallite size (32 nm) is found to be 15 times smaller than the mean grain size (500 nm). Magnetic measurements reveal the strong magnetocaloric effect in vicinity of the Curie temperature T C = 300 K. The considerable magnetic entropy change |ΔSM max | = 1.84 J/(kg K) found for an applied magnetic field of 2 T results in large relative cooling power RCP with a maximum value of 92 J/kg. Peculiar temperature variation of electrical resistivity and negative magnetoresistance are discussed and related to grain sizes and grain boundaries.

Effect of monovalent Na doping on the magnetic properties is studied in Pr0.6Sr0.4−xNaxMnO3 system (x = 0, 0.05) using X-band electron magnetic resonance and magnetization measurements. Temperature variation of magnetic resonance spectra of doped and undoped manganites is analyzed for paramagnetic and ferromagnetic states and compared to similar systems. In paramagnetic phase the magnetic susceptibility proportional to resonance signal intensity is found to obey the Curie–Weiss law. The effective magnetic moment becomes smaller in doped manganite. The paramagnetic Curie temperature derived from signal intensity equals to 312 and 306 K for the undoped and doped manganites, respectively, and is close to values obtained from magnetization variation in paramagnetic phase. The activation energy determined using the adiabatic small polaron hopping model is higher for the undoped than the doped manganite, which proves that the Na doping slightly reduces the Mn3+/Mn4+ double exchange interactions.

Crystals of PrxLa1−xAlO3 solid solution have been grown by the Czochralski method for the first time, to the best of our knowledge. Crystals with high praseodymium concentration tend to grow spirally. The color of the crystals changes with chemical composition. X-ray diffraction shows an increase of the lattice constants with an increase in lanthanum ion concentration. The thermal conductivity has been investigated in the temperature range from 5 to 300 K. Completely different behavior of thermal conductivity is observed at low temperatures for the investigated crystals, whereas it remains roughly constant at high temperatures. The values of magnetic susceptibility lie within the expected range that could be expected for a paramagnetic material.

Structure, magnetic and magnetocaloric properties of poly- and nanocrystalline La0.5Ca0.5MnO3 manganites prepared by the citrate sol–gel method are studied in a broad temperature range. The Arrott plots show that the phase transition is of the second order. The cooling efficiency of 93–97 J/kg is found for the poly- and nanocrystalline samples. The relatively weaker magnetocaloric effect in nanocrystalline La0.5Ca0.5MnO3 is spread over temperature range almost three times broader than for the polycrystalline one. Charge ordering effects decay in manganites with grain sizes below 150 nm.

Magnetic and structural investigation of Fe 80 Zn 20 systems shows that various methods of mechanosynthesis result in fine structures with crystallite sizes between 20 and 100 nm. All the systems studied exhibit strong magnetic ordering with Curie temperatures between 870 and 1000 K. The coercive fields and magnetic energy losses are compared for various milling conditions.

Results of X-ray absorption fine structure measurements in manganites (La 1-x Ho x ) 2/3 Ca 1/3 MnO 3 with 0.15 < x < 0.50 are presented. When LaMnO 3 is doped with a, divalent element such as Ca 2+ , substituting for La 3+ , holes are induced in the filled Mn d orbitais. This leads to a, strong ferromagnetic coupling between Mn sites. Ca ions in La 1-x Ca x MnO 3 introduce a distortion of the crystal lattice and mixed valence Mn ions (Mn 3+ and Mn 4+ ). On the other hand, in manganites (La 1-x Ho x ) 2/3 Ca 1/3 MnO 3 the substitution of La for Ho causes a lattice distortion and induces a disorder, which reduces a magnetic interaction. The ferromagnetic transition temperature and conductivity decrease very quickly with increasing x. The magnetic and transport properties of compounds depend on the local atomic structure around Mn ions. The information on the bond lengths and Debye-Waller factor are obtained from the extended X-ray absorption fine structure (EXAFS) data analysis. The charge state of Mn is determined from the position of the absorption edge in X-ray absorption near edge structure (XANES) data. XAFS results are in good agreement with magnetic characteristics of the studied materials.

Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.

The structural, magnetic and electrical transport properties of the Sn-doped TbMnO3 manganites are studied by X-ray diffraction, ac susceptibility, dc magnetization and electrical resistivity measurements. The Sn doping into the Tb and Mn sites of TbMnO3 compresses the unit cell and changes parameters of the antiferromagnetic phase whereas the magnetic moment of Mn are only weakly affected. The electrical resistivity of doped manganites is reduced and the activation energy EA is determined for the thermally activated conduction.

The sol–gel method is applied to prepare the polycrystalline La 0.8 Sr 0.2 MnO 3 manganite and to reduce grain sizes of nanocrystalline sample down to 23 nm. The magnetocaloric effect was determined from isothermal magnetization measurements. Transition from the polycrystalline to nanocrystalline structure reduces the size of magnetocaloric effect and markedly broadens the temperature interval over which it occurs. The relative cooling power RCP(S) = 35 J/kg in polycrystalline manganite remains almost the same in the nanocrystalline case.

Polycrystalline solid solutions Sr1−xKxPbO3−yFy (0 ≤ x, y ≤ 0.20) were synthesized. Their structural properties were determined by X-ray diffraction. Resistivity and thermoelectric power were measured as functions of temperature. It was shown that a simultaneous substitution of potassium for strontium and fluorine for oxygen results in a transformation of conductivity from semiconductive to metallic at low temperatures. The results are discussed in connection with possible superconductivity in new families of doped perovskites.

The mechanical alloying method was used to prepare Co 60 Fe 30 Ni 10 and Co 50 Fe 35 Ni 15 alloys from the elemental powders. As X-ray diffraction studies proved the final products of milling were the solid solutions with b.c.c . lattice and the average grain size of about 60 nm. After heating of the alloys up to 993 K, the mixtures of two solid solutions with a b.c.c . and f.c.c . lattices were formed. Annealing of the alloys at 1173 K for 1 h resulted in the formation of solid solutions with an f.c.c . lattice. Mossbauer spectroscopy revealed hyperfine magnetic field distributions which reflected the different surroundings of 57 Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of a local environment model. The results of the macroscopic magnetic measurements testified that Co 60 Fe 30 Ni 10 and Co 50 Fe 35 Ni 15 alloys exhibited relatively good soft magnetic properties.

Differential conductance G as a function of the bias voltage V was measured for break-junctions of superconducting Bi2Sr2CaCu2O8+δ and YBa2Cu3O7−δ. The dependences G(V ) for both materials clearly demonstrate the so-called dip–hump structures outside the gap region. A theory, which suggests the charge-density-wave origin of the dip–hump structures and explains its specific form by intrinsic inhomogeneity of cuprate materials, was developed. The well-known pseudogap features in the tunnel spectra of high-Tc oxides found both below and above the superconducting critical temperature are also described by the theory, which testifies that both the pseudogap and the dip–hump structures have the same origin. Competing theories and various G(V ) peculiarities found for a number of superconducting oxides are briefly discussed.

Polycrystalline samples of the La 0.8 Sr 0.2 MnO 3 manganite were prepared by the carbonate precursor method and structurally characterized by X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect is determined and compared to the similar systems. The magnetocaloric effect in polycrystalline manganite is shifted less than 20 K below that one of the single crystal. The relative cooling power being more than one third of RCP(S) for the magnetocaloric standard of metallic Gd suggests a possible application for magnetic cooling around the room temperature.

The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, electrical resistivity and thermoelectric measurements. The isovalent Gd substitution causes that the metal–insulator transition is removed, whereas the negative magnetoresistance effect is weak. The electrical resistivity is described by the small polaron model.

The aim of this work was to obtain bulk nanocrystalline austenitic steel by ball milling of steel powders and their compaction. For powder compaction pulse plasma sintering method was used. Ball milling of 316L austenitic steel powders in a planetary Fritsch P5 mill resulted in the two-phase structure consisting of austenite and martensite. Both phases exhibited crystallite size in the range 10–20 nm. The maximum content of martensite reached 66% and was observed after short processing time. The decrease of its contribution was observed after prolonged milling and was explained by stabilization of nanocrystalline austenite and residual stresses. Pulse current sintering technique allowed obtaining fully dense samples exhibiting austenitic structure characterized by grain size in the range 150–300 nm and microhardness 400 HV 0.3 .

High-energy ball milling technique with subsequent heat treatment were used to prepare the nanocrystalline Fe 41 Ni 20 Co 20 Zr 7 B 12 alloy. The powder samples were obtained by mechanical milling of the melt-spun amorphous ribbon and by mechanical alloying of the mixture of pure elemental powders with the corresponding composition. Combined X-ray diffraction and Mossbauer spectroscopy measurements allowed the structural characterization of the samples. The powder prepared from the ribbon remained amorphous after milling for 27 h, while the milling of the mixture of crystalline elements for 200 h led to the formation of the nanocrystalline iron-based random solid solution. Differential scanning calorimetry results revealed three exothermic peaks, however, crystallization temperatures determined for the nanocrystalline powder were much lower that those obtained for the amorphous one. The first two stages correspond to the formation of the bcc FeCo nanograins. Annealing at higher temperatures caused the crystallization of the bcc phase followed by the formation of the iron-based borides. The magnetization measurements performed as a function of temperature confirmed the amorphous and crystalline states of the ball milled ribbon and mechanically alloyed elemental powders, respectively. The Curie temperature of the amorphous ribbon is markedly higher than that of the amorphous powder.

We compare structure and magnetic parameters of the polycrystalline and nanocrystalline manganites La 0.75 Ca 0.25 MnO 3 prepared by the carbonate precipitation and the sol–gel methods, respectively. The Curie temperature is surprisingly enhanced for nanocrystalline manganite. An effect of magnetic fields on transport parameters is analyzed for the metallic and semiconducting ranges.

Mechanically synthesised Ni and Co-base alloys exhibit interesting magnetic properties, suggesting their potential applications. The equilibrium Ni–Ge and Co–Ge phase diagrams reveal the existance of Ni 5 Ge 3 and Co 5 Ge 3 phases, both exhibiting high and low-temperature modifications. The purpose of this work was to synthesise by mechanical alloying the Ni 5 Ge 3 and Co 5 Ge 3 alloys and to study their structure and magnetic properties. Mechanical alloying processes performed for Ni 62 Ge 38 and Co 62 Ge 38 powder mixtures resulted in the formation of single phase Ni 5 Ge 3 and Co 5 Ge 3 nanocrystalline alloys after 20–50 h of processing. Ni 62 Ge 38 alloy was ferromagnetically ordered for all milling times. In the case of Co–Ge alloy, magnetization measurements showed an evolution from ferromagnetic to paramagnetic ordering upon milling.

Samples of La0.7Ca0.3Mn1-xGaxO3 with x = 0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behavior of the x = 0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn3+/Mn4+ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping., Comment: submitted to J Magnet Magnet Mater; 13 figures; 2 tables; 38 references