G. Kallias's research while affiliated with National Center for Scientific Research Demokritos and other places

Publications (73)

Article
La0.8Sr0.2Co1−xFexO3 (x=0.15, 0.2, 0.3) samples were studied by means of AC magnetic susceptibility, magnetization, magnetoresistance and 57Fe Mössbauer spectrometry. Iron was found to take on a high spin 3d5−α electronic state in each of the samples, where α refers to a partly delocalized 3d electron. The compounds were found to exhibit a spin-clu...
Article
We have studied the phase diagram of La1-xCaxMnO3 for 0.5⩽x⩽0.9 using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry Pnma. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On furth...
Article
In the last decade the discovery of colossal magnetoresistance in Mn based perovskites brought various perovskite and spinel materials, displaying the effect of magnetoresistance, into the center of scientific interest. The physical and chemical effects, underlying the phenomenon of negative magnetoresistance in these compounds, are not yet fully u...
Article
The temperature dependence of the 57Fe Mössbauer recoilless fraction, and that of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr2S4 have been studied in detail around the Curie temperature with the help of 57Fe Mössbauer spectroscopy. Ferrimagnetic order was found to break down anomalously at ∼20 K below the Curie t...
Chapter
Manganese perovskites, with the general formula REMnO3 (RE=Rare Earth), display a wealth of new phenomena on substitution of part of the trivalent RE by a divalention of the alcaline earth series (Ca, Sr etc.). This doping results in the formation of a mixed valence system (Mn3+ , Mn4+) with a rich phase diagram with ferromagnetic insulators at low...
Article
Most of the models purporting to explain the intriguing observation of colossal magnetoresistivity (CMR) in manganites invoke double exchange (DE) electron transfer between Mn3+ and Mn4+ ions, and coupling between the itinerant electrons and the dynamic Jahn-Teller (J-T) lattice distortions. Here we report using Mössbauer spectroscopy some very rev...
Article
The temperature dependence of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr2S4 has been studied in detail around the Curie temperature with the help of 57Fe Mssbauer spectroscopy. Ferrimagnetic order was found to break down anomalously at ≅ 20 K below the Curie temperature in FeCr2S4. Magnetic relaxation of iron ma...
Article
We report on magnetometry, resistivity and Mössbauer spectroscopy measurements on single-phase Fe3BO5 in a wide temperature range from 4.2 to 620 K. Magnetically split Mössbauer spectra were observed below TN = 114 K, although a proportion of the Fe2+ ions in the basal plane (crystallographic site Fe1) remain paramagnetic down to the ferrimagnetic...
Article
We have studied La1-xCaxMnO3 (x=0.5,0.6) using 57Fe Mössbauer spectroscopy and magnetic moment measurements. The Mössbauer spectra below TN=140 K (125 K for the x=0.6 sample) were interpreted with static distributions of the hyperfine magnetic field at the Fe nucleus, except close to TN where a spin relaxation model was employed. Above TN the quadr...
Article
We studied the crystal and magnetic structure of the La1-xCaxMnO3 compound for x=0.8 and x=0.85. At T=300 K both samples are paramagnetic with crystallographic symmetry Pnma. At low temperatures they undergo a monoclinic distortion from orthorhombic Pnma-type structure with ap√2x2apxap√2 to a monoclinic structure with (ap√2x2apxap√2, β=90+ε∼91.4°)...
Article
Full-text available
We studied the crystal and magnetic structure of the La1-xCaxMnO3 compound for x=0.8 and x=0.85. At T=300 K both samples are paramagnetic with crystallographic symmetry Pnma. At low temperatures they undergo a monoclinic distortion from orthorhombic Pnma-type structure with ap√2×2ap×ap√2 to a monoclinic structure with (ap√2×2ap×ap√2, β=90+ɛ∼91.4o)...
Article
Full-text available
In their Comment Savosta and Novak claim that the doubly peaked {sup 55}Mn NMR line shape observed in La{sub 0.67}Ca{sub 0.33}MnO{sub 3} for T{lt}70 K [Phys. Rev. B >58, 12237 (1998)] is not real, but an artifact resulting from the experimental conditions. In support to their arguments, they present {sup 55}Mn line-shape measurements at 77 K. In th...
Article
1%Sn-119-doped La0.5Ca0.5MnO3 was studied by Mossbauer spectroscopy, magnetic moment, and resistivity measurements. The Mossbauer spectra below the charge-ordering temperature are explained with ferromagnetic, antiferromagnetic. and ferromagnetic spin cluster components. The magnetic and thermal hystereses of the relative intensities of the compone...
Article
The relaxation of the magnetic moment of a thin disk of YBa2Cu3O7−δ superconductor in a perpendicular magnetic field shows a logarithmic dependence on time for the examined temperature range . The analysis of the relaxation data is done within an analytical model. The field and temperature dependencies of the critical current jc and the pinning pot...
Chapter
Ferrospinel oxide powders were obtained by co-precipitation in alkaline medium of Fe3+ and Cu2+ cations from water solutions of chlorides of these elements. Two kinds of Cu-spinel powders were synthesized— cubic and tetragonal— depending on the Cu/Fe ratio in the solution. The size of the particles was about 6.5 nm. The Moessbauer analysis showed s...
Article
1%119Sn-doped La0.5Ca0.5MnO3 was studied by Mössbauer spectroscopy, magnetic moment, and resistivity measurements. The Mössbauer spectra below the charge-ordering temperature are explained with ferromagnetic, antiferromagnetic, and ferromagnetic spin cluster components. The magnetic and thermal hystereses of the relative intensities of the componen...
Article
Full-text available
1% $^{119}$Sn-doped La$_{0.5}$Ca$_{0.5}$MnO$_3$ was studied by M\"ossbauer spectroscopy, magnetic moment and resistivity measurements. The M\"ossbauer spectra below the charge-ordering temperature are explained with ferromagnetic (FM), antiferromagnetic (AF), and ferromagnetic spin cluster (CL) components. The magnetic and thermal hystereses of the...
Article
Isothermal global magnetic measurements in a detwinned YBa2Cu3O7−δ single crystal revealed an abrupt change in the slope of the increasing part of the virgin magnetization curves (M(H)). The temperature dependence of the magnetic field H3 at which this feature occurs decreases with temperature from 5 up to 40 K and after for T > 40 K increases. For...
Article
We have studied the vortex creep in YBaCuO single crystals at high temperatures, T>80 K, by dc-current resistivity measurements. The obtained results show single vortex creep for low magnetic fields, creep of vortex bundles in intermediate field region, whereas in high magnetic fields plastic creep mediated by motion of the flux-line-lattice (FLL)...
Article
Magnetic field mapping measurements were performed using commercial high-Tc superconducting quantum interference device (SQUID) sensors. The sensors are incorporated in a fully computerized scanning system and were found to be operative only when encased inside a double-layer mu-metal shield. This allowed us to measure signals of the order of 0.5 n...
Article
Isothermal global magnetic measurements in a detwinned YBa2Cu3O7-δ single crystal reveal a jump in the slope of the increasing part of the virgin magnetization curves. This feature is broadened or even disappears at low temperatures (T<15 K). At high temperatures (T>75 K) and below the Hsp(T) curve in the obtained vortex-matter phase diagram, it is...
Article
We performed magnetic moment (m) relaxation measurements at low temperatures (5⩽T⩽20K) in two single phase, c-axis-oriented polycrystalline Bi1.7Pb0.3Sr2Ca2Cu3O10+δ (2223) samples prepared under different conditions with different Tc's. The m versus t data show a logarithmic relation and by fitting them the Jc(H,T) and Uc(H,T) variation were extrac...
Article
Vortex creep anisotropy was studied with DC-current resistivity measurements. It is found that the activation energy for the plastic creep increases when magnetic field vector is turned off the /c-axis, in agreement with performed calculations.
Article
The relaxation of the magnetic moment of a thin disk of YBa2Cu3O7-δ superconductor in a perpendicular magnetic field shows a logarithmic dependence on time for the examined temperature range T:10-60 K. Data are analyzed within an analytical model. The temperature dependencies of the critical current jc, and the pinning potential U0, are estimated b...
Article
The influence of tellurium (Te) addition to the Bi-Pb-Sr-Ca-Cu-O (B(Pb)SCCO) system on its microstructure and phase formation is investigated. Electron probe microanalysis and scanning electron microscopy analyses show Te diffusion from the superconducting core into the silver sheath of the B(Pb)SCCO tapes. It is established that the initial Te pre...
Article
139La NMR spin-lattice relaxation rate 1/T1 and rf enhancement experiments provide evidence that the low temperature regime of the ferromagnetic (FM) phase of La1-xCaxMnO3 segregates into highly-conductive and poorly-conductive FM regions, associated with differences in the orbital structure. Remarkably, phase separation is accompanied with the app...
Article
We have performed elastic neutron diffraction and magnetization measurements on the perovskite manganite La1−xCaxMnO3 at half-doping (x=12) under a 40kOe magnetic field both upon cooling and warming (2⩽T⩽300K). The magnetization data upon cooling under 40kOe revealed a paramagnetic-to-ferromagnetic (FM) transition at Tc≈235K and then a first-order...
Article
Full-text available
55Mn NMR line shape measurements in La1-xCaxMnO3 for 0.20< or =x< or =0.50 provide experimental evidence about the existence of two distinct regions in the T-x magnetic phase diagram, where the homogeneous ferromagnetic (FM) metallic state is separated into FM metallic and FM insulating regions. These results are in agreement with recent theoretica...
Article
We present magnetic field mapping measurements performed with commercial high-Tc superconducting quantum interference device (SQUID) sensors. Our aim was to make an initial assessment of the capabilities of our commercial high-Tc sensors (and of the entire system incorporating them) under zero applied magnetic field. This allowed us to measure sign...
Article
Polycrystalline Fe2 BO4 prepared by solid-state reaction was investigated over a wide temperature range using Mössbauer spectroscopy and magnetization and resistivity measurements. The Mössbauer data below 270 K reveal four iron sites (two Fe2+ and two Fe3+ ) in a 1:1:1:1 ratio. Above this temperature, electron delocalization sets in between the di...
Article
Full-text available
We investigated the flux-creep behaviour of a thin disc of YBa2Cu3O7- superconductor in the framework of an analytical model, in the temperature range T = 10-60 K and for a perpendicular applied field Ha = 5-50 kG. The relaxation of the magnetic moment shows a logarithmic dependence on time for the whole temperature range. The field and temperature...
Article
Low hysteresis, giant magnetoresistance (GMR) sputtered Co/Cu multilayers were employed in a 2×4 array of sensing elements. Patterning was performed by optical lithography, using the lift-off technique. To assess the applicability of this sensor, magnetic field mapping of a ring-magnet was performed with a computer controlled scanning system and th...
Article
The temperature and magnetic-field dependence of activation energy Uo(T,H) for creep has been studied in an HgBa2CuO4+δ single crystal below and above the “fishtail” peak Hsp(T). At constant temperature, Uo(H) increases up to Hsp/(T) and then for H>Hsp/(T) it decreases. Hsp/(T) is located lower than the field Hsp(T) deduced from the hysteresis loop...
Article
The irreversibility magnetic field H-irr(T) decreases exponentially in the temperature range 20 less than or equal to T less than or equal to 88 K. At T* approximate to 88 K, the H-irr(T) curve changes slope abruptly and a new mechanism controls the irreversibility up to T-c. The hysteresis loops measurements (H parallel to c) show a second peak fo...
Article
We estimated the irreversibility line using dc magnetic measurements in an optimally doped (Tc~109 K) and an oxygen reduced (Tc~104 K) single phase c-axis oriented powder Bi1.7Pb0.3Sr2Ca2Cu3O10+delta sample. We observed a nearly exponential dependence of Hirr on temperature for both samples, but close to Tc the slope of the Hirr(T) changes abruptly...
Article
Current–voltage characteristics (CVC's) of YBa2Cu3O6.95 single crystal were measured for dc-current densities up to 3×104 A/cm2. The depinning critical current Jcd was estimated within the Bardeen–Stephen model and no anomalous behavior was observed in Jcd(H) in contrast to the fishtail behavior of the critical current JcE determined on the electri...
Article
57Fe Mössbauer measurements and magnetization data were used to study both microscopically and macroscopically the first-order antiferromagnet-to-ferromagnet (AFM-FM) transition observed in La0.5Ca0.5MnO3. The zero field cooled and field cooled Mössbauer spectra for H ≥ 40 kOe are extremely history dependent and can be fitted by predominantly AFM a...
Article
Low-temperature La-139 and Mn-55 NMR line shape measurements in La1-xCaxMnO3 for 0.125 less than or equal to x less than or equal to 0.5, and La-0.67(Ca1-yBay)(0.33)MnO3 for 0 less than or equal to y less than or equal to 1 are shown to directly reflect changes of the structure and of the magnetic state at a local level. For low x values in La1-xCa...
Article
La2/3Ca1/3MnO3 doped with Fe were studied by Mössbauer spectroscopy and neutron powder diffraction. The Mössbauer spectra (MS) reveal that Fe substitutes for Mn as Fe3+ (S=5/2) and is antiferromagnetically coupled to the Mn host lattice. The magnetic behavior, from the neutron diffraction data, is that of a typical 3D Heisenberg ferromagnet. The te...
Article
The first order antiferromagnet (AFM) to ferromagnet (FM) transition observed in La0.5Ca0.5MnO3 compound has been studied, both macroscopically and microscopically, by magnetization and 57Fe Mössbauer measurements. The Mössbauer spectra reveal that Fe substitutes for Mn3+ as Fe3+ (S=5/2). The zero-field-cooled and field-cooled Mössbauer spectra for...
Article
The first order antiferromagnet (AFM) to ferromagnet (FM) transition observed in La0.5Ca0.5MnO3 compound has been studied, both macroscopically and microscopically, by magnetization and 57Fe Mössbauer measurements. The Mössbauer spectra reveal that Fe substitutes for Mn3+ as Fe3+ (S=5/2). The zero-field-cooled and field-cooled Mössbauer spectra for...
Chapter
The study of the magnetic properties of mixed valence manganese perovskites dates back almost 50 years [1–2]. The existence of competitive ferromagnetic (FM) double-exchange [3] and antiferromagnetic (AF) superexchange interactions, which are very sensitive to the structural parameters and the degree of doping, results in a very rich magnetic phase...
Article
Full-text available
In this work, we have studied the crystal and magnetic structure of fully deoxygenated using neutron powder diffraction data. Rietveld profile refinement confirmed the presence of removable oxygen y within the Cu(1) layers. While for the fully oxygenated sample the space group describes the crystal structure adequately, for the deoxygenated sample...
Article
We have studied the crystal structure and the magnetic properties of the oxygen-deficient perovskite using x-ray and neutron powder diffraction, and Mössbauer spectroscopy. The neutron diffraction data have shown antiferromagnetic long-range order described with two propagation vectors and . Mössbauer spectroscopy for revealed the existence of two...
Article
The authors present a systematic study of the lattice parameters and of the superconducting behaviour of the YBa2Cu3-xMnxOy superconductor as a function of both the Mn doping and the oxygen content. The orthorhombic structure is preserved throughout the substituted range and the Tc is very little affected by the Mn content. The Tc values of the dop...
Article
55Mn and 139La NMR line shape and spin-spin relaxation time T2 measurements on polycrystalline La0.67Ca0.33MnO3 were carried out as a function of temperature. For T<80K the 55Mn NMR line shapes have been attributed to spatial encoding of the NMR frequency due to variation of the charge-carrier (hole) density across domain walls. For T>80K walls are...
Article
The vortex phase diagram in HgBa2CuO4+δ single crystals (Tc=95 K) is investigated using dc-magnetic measurements. The irreversibility magnetic field Hirr(T) decreases exponentially in the temperature range 20<=T<=88 K. At T*~88 K, the Hirr(T) curve changes slope abruptly and a new mechanism controls the irreversibility up to Tc. Magnetization versu...
Article
We have studied the magnetic structure of the oxygen reduced YSr2Cu3-xFexO6+y (x=0.8 and 1) compound. Three-dimensional (3D) long-range antiferromagnetism was observed and was indexed with propagation vector k=(1/2 1/2 1/2). The only peak with non-zero intensity was (1/2 1/2 3/2). The temperature variation of the thermal average magnetic moment per...
Article
The current-voltage characteristics (CVC's) of YBa2Cu3O6.95 single crystal with unidirectional twins were measured in external magnetic field inclined with respect to twin planes under the angle 45°. Current, magnetic-field, and temperature dependences of the pinning potential U(J,B,T) and magnetic-field and temperature dependences of the depinning...
Article
Films deposited by pulsed laser ablation from La2/3Ca1/3MnO3 targets exhibit a large variety of properties depending on the exact preparation conditions. The as-deposited films at high enough oxygen pressures PO2, have transition temperatures (Tc) close to that of the target material (265 K). At lower PO2 the films can be made to have lower Tc's bu...
Article
Spin fluctuations in two samples of the La2/3Ca1/3MnO3 system doped with 1% 57Fe and 5% Sn were studied by Mössbauer spectroscopy. Fe substitutes for Mn3+ and Sn for Mn4+. A charge redistribution occurs between 4.2 K and Tc. The charge carrier concentration defines magnetic regions with different coupling constants which fluctuate with relaxation r...
Article
The substitution of Fe for Cu stabilizes the structure of Ba2InCuO4 + y and an order-to-disorder structural transformation is observed upon varying the preparation conditions. This variation occurs either by heating the ordered phase at higher temperature in air or by heating it in Ar atmosphere during thermogravimetry experiments. Mössbauer spectr...
Article
139La NMR in a zero external magnetic field has been used as a probe in order to study the Mn spin ordering of La0.5Ca0.5MnO3. For T<Tc two different spin configurations are detected, assigned to a ferromagnetic and an antiferromagnetic one, which persist down to the lowest measured temperature T=90nK. Close to Tc strong coherent spin fluctuations...
Article
The substitution of Fe for Cu stabilizes the structure of Ba2InCuO4 + y and an order-to-disorder structural transformation is observed upon varying the preparation conditions. This variation occurs either by heating the ordered phase at higher temperature in air or by heating it in Ar atmosphere during thermogravimetry experiments. Mössbauer spectr...
Article
139La NMR in a zero external magnetic field has been used as a probe in order to study the Mn spin ordering of La0.5Ca0.5MnO3. For T<TC two different spin configurations are detected, assigned to a ferromagnetic and an antiferromagnetic one, which persist down to the lowest measured temperature T= 90 K. Close to Tc strong coherent spin fluctuations...
Article
The substitution of Fe for Cu stabilizes the structure of Ba{sub 2}InCuO{sub 4+y} and an order-to-disorder structural transformation is observed upon varying the preparation conditions. This variation occurs either by heating the ordered phase at higher temperature in air or by heating it in Ar atmosphere during thermogravimetry experiments. Moessb...
Article
We studied the crystal and magnetic structure of the oxygen deficient perovskite YSrCuFeO5+y. The structure was refined from neutron powder diffraction data by assuming both substitutional and displacement disorder. Three-dimensional (3D) antiferromagnetism with TN = 400 ± 10 K occurs and all the magnetic peaks were indexed with two propagation vec...
Article
A thorough study of the Mössbauer spectra (MS) of a lightly iron doped (2%) polycrystalline La <sub> 0.75 </sub> Ca <sub> 0.25 </sub> MnO <sub> 3 </sub> compound has been carried out from T=4.2 K up to 300 K. The MS for T≫T<sub>c</sub> and at T=4.2 K show one component. The corresponding hyperfine parameters are compatible with S=5/2 Fe <sup>3+</su...
Article
A thorough study of the M{umlt o}ssbauer spectra (MS) of a lightly iron doped (2{percent}) polycrystalline La{sub 0.75}Ca{sub 0.25}MnO{sub 3} compound has been carried out from T=4.2 K up to 300 K. The MS for T{gt}T{sub c} and at T=4.2 K show one component. The corresponding hyperfine parameters are compatible with S=5/2 Fe{sup 3+} in octahedral co...
Article
The substitution of Fe for Cu stabilizes the structure of BaâInCuO{sub 4+y} and an order-to-disorder structural transformation is observed upon varying the preparation conditions. This variation occurs either by heating the ordered phase at higher temperature in air or by heating it in Ar atmosphere during thermogravimetry experiments. Moessbauer s...
Article
We studied the structure and the magnetic properties of the oxygen deficient perovskite PrBaCuFeO5+y as a function of the removable oxygen y. The average crystal structure was refined from x-ray and neutron powder diffraction data which both confirm the presence of the additional oxygen y in the Pr layer. Long-range three-dimensional (3D) antiferro...
Article
RBa2Cu3O7 and [R0.5Pr0.5]Ba2Cu3O7 compounds with RY and lanthanides have been prepared and studied at ambient temperature by means of XRD and infrared-reflectance spectroscopy. In Pr free compounds, increasing the Shannon radius of R, rR, leaves the puckering of the Cu(2)−O(2, 3) sheet unaffected. In the Pr containing compounds, the PrO coordinat...
Article
Full-text available
The crystal structure and physical properties for (Y,Ce)âSrâCuâFeO{sub 8+{ital y}} compound are reported using Rietveld-refinement of x-ray powder-diffraction data, dc magnetic susceptibility, Moessbauer, and Raman spectroscopy measurements. Moessbauer data can be analyzed with three components. Component {ital A} is attributed to Fe{sup 3+} ({ital...
Article
Resistive transitions and current–voltage characteristics of aluminum-doped YBaCuO single crystals containing unidirectional twins have been investigated in magnetic fields. Temperature, field, and angular dependences of the critical current and effective pinning potential are discussed in the frames of the theory of collective pinning at small-sca...
Article
We have studied the crystal structure, the site occupancy of iron at the Cu(1), Cu(2) positions and the magnetic properties of the YSr2Cu3−xFexOy system (x=0.25 upto 1) by using X-ray diffraction, Mössbauer spectroscopy and magnetic-susceptibility data. The system is superconducting with Tc=40, 30 and 20 K forx=0.25, 0.30 and 0.35, respectively, wh...
Article
We report systematic measurements of the resistivity and of the Hall coefficient RH of bulk YBa2Cu3-xFexOy by varying both the iron doping and the oxygen concentration and for temperatures ranging from 100 to 250 K. The Hall number ncell (at 100 and 200 K) decreases linearly with decreasing y for all x and exponentially upon Fe doping. The temperat...
Article
Mössbauer spectroscopy, magnetic susceptibility, and Rietveld analysis were used to study the magnetic and structural properties of YSr2Cu2FeOy prepared under different annealing conditions. The structure was refined using the tetragonal space group P4/mmm for both the O2 and the Ar postannealed samples. Mössbauer analysis shows that Fe is equally...
Article
Mössbauer spectroscopy, magnetic susceptibility, and Rietveld analysis were used to study the magnetic and structural properties of YSr2Cu2FeOy prepared under different annealing conditions. The structure was refined using the tetragonal space group P4/mmm for both the O2 and the Ar postannealed samples. Mössbauer analysis shows that Fe is equally...
Article
We present the results of thermogravimetric and 57Fe Mössbauer studies of the oxygen deficient perovskite REBaCuFeO5+x series with RE = Y, Nd, Sm, Gd, Dy, Tm, Lu. The presence of the removable content x of oxygen was determined by analysis of TGA measurements in a stream of Ar gas. The amount of removable oxygen was highest for the Nd compound and...
Article
The non-superconducting, antiferromagnetic compound LuBaCuFeO5+x has been studied. The 57Fe Mössbauer measurements revealed Fe3+ to be in the high spin state and TN to be below 485 K. The fit of the X-ray diffraction spectra, by means of the Rietveld method, is better than that found by considering the space group P4mm. TGA revealed a weight loss o...
Article
We have studied the non superconducting phase REBaCuFeO5+x (where RE=rare earth). with neutron, x-ray powder diffraction and Mössbauer spectroscopy.
Article
We present a systematic study of the variation of the lattice parameters and the Tc of the YBa2Cu3-xMnxOy superconductor with both the Mn and the oxygen content. The structure remains orthorombic and the Tc is very little affected from the Mn content. The effect of the oxygen content for various Mn doping contents is also discussed as well as wheth...
Article
A systematic study is presented of the lattice parameters and the transition temperature Tc of the YBa2Cu3−xFex 0y superconductor as a function of both the iron and the oxygen content. The system undergoes an orthorhombic to tetragonal structural transition with increasing iron content, however remaining superconducting. The Tc values of the doped...

Citations

... The curves exhibit a conspicuous peak at H smp that is known as the second magnetization peak (SMP). Second magnetization peaks have been reported in studies of most classes of superconductors, including low-T c [21,22], iron-based [23][24][25][26][27][28][29][30][31][32][33], and highly anisotropic [34,35] materials and other cuprates [29,[36][37][38][39] as well as previous work on Hg1201 [18,[40][41][42][43][44]. This peak is typically thought to originate from a crossover between vortex pinning regimes, such as elastic-to-plastic transitions [23,25,26,28], structural phase transitions [45][46][47][48] in the vortex lattice, or dimensional crossovers. ...
... Recently much interest has been paid to the double perovskite oxide YBaCuFeO 5+δ [1][2][3][4][5][6][7][8][9]. This oxide was found to consist of a CuFeO 10 bilayer of corner-sharing CuO 5 and FeO 5 square pyramids as schematic shown in Fig. 1 [8,9]. ...
... Very often the region defined as the plateau in the S(T) behavior is characterized by the presence of a minimum 14,16,18,19 , also visible in the field dependence of the creep rate S(H) 16,[18][19][20] . Independently of the class of the superconductor, these creep rate characteristics have been often reported in concomitance with the presence of the second magnetization peak (or just simply "peak effect") phenomenon 17,18,[20][21][22][23][24][25][26][27][28] . It is necessary to consider that in literature it is common to find both the notations "Second Magnetization Peak" 15,22,29 and "Peak Effect" 18,[30][31][32] for this kind of phenomena where the peak in the field dependence of the critical current density occurs away from H c2 . ...
... %) and La-Ca manganites (Fe content: 0.00-0.02 at.%) was observed in [20,21]. The decrease in the cell parameters was accounted for by spin excitations localized around the impurity Fe 3+ ion and its transition to low-spin state with a decrease in its effective radius [21]. ...
... several double perovskites were reported in the literature to exhibit a perovskite structure despite having a large amount of oxygen vacancies such as YBaCuFeO 5þδ , PrBaCuFeO 5þδ , LuBaCuFeO 5þδ , and LaBaFeCuO 5þδ . [24][25][26][27] So, it might be possible for the system to have such a high value of δ. Furthermore, high-temperature XRD results (Figure 3b) clearly indicate that the single-phase perovskite structure is stabilized and holds up to at least 973 K, which the TGA result reconfirms as well. ...
... ossbauer spectroscopy (11,12). The data obtained by these techniques provided evidence that the members of this series are isostructural to the tetragonal YBCFO. ...
... The dominating sextet with intensive resonance lines has a hyperfine field value of $50 T and d = 0.45 mm/s (at RT). This sextet looks very similar to low temperature pictures for La 0.5 Ca 0.5 -Mn 1-x Fe x O 3 manganites with a very small amount of Fe (x = 0.01), which show a full magnetic ordering below 50 K [7]. Connection between the paramagnetic doublet and the dominated magnetic sextet is confirmed by an intensity ratio behavior: the I PM /I M ratio increases with temperature increasing. ...
... The unit cells of both compounds contain a fluorite block that is similar to the R 2-x Ce x CuO 4 electron-doped superconducting cuprates that have CuO 2 planes where the fluorite blocks are separated by perovskite ASrO 3-y where A is Ru for Ru1222 and A is Fe for Fe1222. The absence of superconductivity and the strong localisation observed in Fe1222 with x = 0.7 [1] is likely to be due to Fe and Cu antisite disorder [4][5][6] where there is some Fe on the CuO 2 plane and some Cu on the FeO 2-y plane as well as oxygen disorder and vacancies in the FeO 2-y plane where δ~0.8 in oxygen loaded x = 0.5 samples [4][5][6]. ...
... A distribution in the size of these domains furthermore leads to a distribution in the hyperfine magnetic field already before the collapsed paramagnetic peak appears. This effect is also clearly visible in the Mössbauer spectra of Fe 0.5 Cu 0.5 Cr 2 S 4 taken at temperatures in the range from 320 K to alignment as a response to an externally applied magnetic field, is thought to play a role in the realization of a pronounced CMR effect in the neighborhood of the Curie temperature in CMR materials [15,26]. ...