Transport and Magnetic Properties of Eu and Sr Doped Manganite Compound La0.7Ca0.3MnO3

The effect of simultaneous increase in carrier density and size-disorder on the transport and magnetic properties of La_0.7Ca_0.3MnO₃ has been investigated by studying the (La_{0.7 − 2x} Eu _x )(Ca_0.3Sr _x )MnO₃ (0.05 ≤ x ≤ 0.2) (LECSMO) compounds. These compounds have been compared with standard La_{1 − x} Ca _x MnO₃ (0.3 ≤ x ≤ 0.5) (LCMO) in which carrier density alone varies. In LECSMO, the insulator-metal transition temperature (T _p) decreases from 180 K for x = 0.05 to 80 K for x = 0.15 sample vis-à-vis ∼240 K for x = 0.35 to ∼225 K for x = 0.45 in LCMO system. Similarly, the Curie temperature (T _C) in LECSMO, decreases from 205 K for x = 0.05 to 75 K for x = 0.2 sample against 240 K for x = 0.35 to ∼220 K for x = 0.45 in LCMO system. Also, in LCMO the T _C and T _p are coincident whereas, in LECSMO system, with increasing x there is an increasing disparity between the two. At 5 K, in the metallic region, a large MR (>90%) is observed in x = 0.15 sample and is discussed in terms of phase segregation and inter-grain magnetoresistance.     

Phase transitions and dielectric relaxation in (1 − <Emphasis Type="Italic">x</Emphasis>)SrTiO<Subscript>3</Subscript>-<Emphasis Type="Italic">x</Emphasis>BiFeO<Subscript>3</Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.04)

The dielectric and acoustic properties of (1 − x)SrTiO₃-xBiFeO₃ (0 ≤ x ≤ 0.04) solid solutions have been studied in the temperature range 10–300 K. The polar state exhibiting permittivity dispersion and dielectric hysteresis loops has been revealed at temperatures of 40–100 K. At 20–40 K, we have observed one more dielectric relaxation, which is not associated with the polar state and vanishes at a concentration of the second solid-solution component x = 0.04. The antiferrodistorsive transition has been found to vary with increasing concentration x. At temperatures below the antiferrodistorsive transition point, the polar (relaxor) state has been shown to persist in all the measured solid solutions.     

A μSR and neutron polarisation analysis study of Mn moment delocalisation in Fe substituted YMn2

Neutron polarisation analysis measurements reveal antiferromagnetic spin correlations persisting to temperatures of 120 K in Pauli paramagnetic Y(Mn_1−x Fe _x )₂, 0.03≤x≤0.05. The mean moment at the Mn(Fe) site is found to be 0.2μ _B. Transverse field μSR is characterised by weak exponential damping with a rate of 0.02 μs⁻¹ at 300 K increasing according to the power lawT ^−0.75 to only 0.16μ _S ⁻¹ at 12 K. It is suggested that these results are consistent with a slowing down of longitudinal spin fluctuations at the Mn site as temperature decreases.     

Dielectric spectroscopy of PbZr1 ? xTixO3 solid solutions (0.495 ≤ x ≤ 0.51) in a temperature range of 100–300 K at frequencies from 1 × 10?2 to 2 × 107 Hz

The behavior of the relative permittivity ɛ/ɛ₀ of PbZr_{1 − x} Ti _x O₃ (PZT) solid solutions (0.495 ≤ x ≤ 0.51) in the temperature range of 100–300 K at frequencies from 1 × 10⁻² to 2 × 10⁷ Hz was investigated. Diffuse, strongly relaxing maxima at T = 230−260 K (x = 0.495−0.505) and 150–160 K (x = 0.510) were observed in the PZT studied. The relaxation processes are well described by the Vogel-Fulcher law, and the dielectric spectra are approximated by the Cole-Cole formula.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Large pyroelectric response in (Pb0.87La0.02Ba0.1)(Zr0.7Sn0.3−x Ti x )O3 antiferroelectric ceramics under DC bias field

(Pb_0.87La_0.02Ba_0.1)(Zr_0.7Sn_0.3−x Ti _x )O₃ (PLBZST, 0.06≤x≤0.09) antiferroelectric ceramics were fabricated by conventional solid state reaction process, and their ferroelectric, dielectric, and pyroelectric properties were systemically investigated. PLBZST with different Ti content were all confirmed to be in an antiferroelectric phase at T=50°C, which is close to the lowest phase transition temperature. Compared with conventional FE ceramics, PLBZST antiferroelectric ceramics exhibited higher electric field induced pyroelectric coefficient (p). As the content of Ti increased from 0.06 to 0.09, the pyroelectric coefficient increased from 1000 to 6500 μC/m²K under a 500 V/mm DC bias field. The maximum pyroelectric coefficient of 8400 μC/m²K was obtained at x=0.09 when an 850 V/mm DC bias field was applied, which is far larger than that of conventional phase transition pyroelectric materials. Large pyroelectric response is beneficial for the development of infrared detectors and thermal imaging sensors.     

Transmission spectra of epitaxial layers of Pb1 ? xEuxTe (0 ≤ x ≤ 0.37) solid solutions in the frequency range 7–4000 cm?1

The spectra of epitaxial Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.37) solid solution layers grown on BaF₂ and Si substrates have been investigated over a wide frequency range 7–4000 cm⁻¹ at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm⁻¹. As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm⁻¹.     

Muon spin relaxation study on magnetism in high quality single crystal of a high transition temperature superconductor La2−xSrxCuO4−σ (0.11≤x≤0.14)

The positive muon spin relaxation method is applied to probe magnetic ordering in the superconducting phase of a high quality single crystal of La_2−xSr_xCuO_4−σ (0.11≤x≤0.14). The well characterized crystal ofx=0.11 (T _c=34.5 K) with nearly complete flux exclusion exhibits spin freezing at 8K(T _f) with significant spin fluctuation up to 20 K. The onset of spin fluctuation andT _f decrease against increasingx towardsx=0.15, suggesting an existence of a magnetic phase boundary aroundx whereT _c becomes maximum.     

Kinetic properties of Ni<Subscript>3</Subscript>Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys in the range of transition from band to spin-localized ferromagnetism

The kinetic properties of ferromagnetic Ni₃Al_{1 − x} Mn _x alloys with _x ≤ 0.6 are studied at T ≤ 800 K and H ≤ 7 MA/m. The behavior of the electrical resistivity, the thermopower, the magnetoresistance, the Hall effect, and the spontaneous Hall effect are analyzed in the range of transition from band (Ni₃Al) to spinlocalized (Ni₃Mn) ferromagnetism at x ∼ 0.15.     

Low-temperature conductivity and the Hall effect in (PbzSn1 ? z)0.84In0.16Te semiconducting solid solutions

The temperature dependences of the conductivity and the Hall effect in heavily doped polycrystalline samples of the (Pb _z Sn_{1 − z} )_0.84In_0.16Te solid solutions with lead content varied within the 0 ≤ z ≤ 0.9 interval have been studied. For x ≤ 0.65, the material undergoes a superconducting transition at a critical temperature T _c ≤ 4.2 K in a magnetic field H _c2(0 K) ∼ 50 kOe. As the lead concentration is increased to z ≤ 0.9, a clearly pronounced trend to transfer of the material to the dielectric state is observed at helium temperatures. The observed behavior is related to the variation in the band structure of the solid solutions with variations in the material composition, doping level, and position of the indium impurity band. The dependences of the resistivity, Hall effect, and superconducting characteristics of (Pb _z Sn_{1 − z} )_0.84In_0.16Te on the temperature and the composition of the solid solutions is observed to be related to the variation in its band structure as tin atoms are replaced with lead in the metallic sublattice of the compound. Original Russian Text ? D.V. Shamshur, S.A. Nemov, R.V. Parfen’ev, M.S. Kononchuk, V.I. Nizhankovskii, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 11, pp. 1948–1952.     

Thermal and magnetic properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

The thermodynamic and magnetic properties of the La_{1 − x} Pb _x MnO₃ (0.24 ≤ x ≤ 0.40) solid solution system were investigated in the temperature range of 4.2–340 K. All objects were ferromagnetics with Curie temperature T _C ≈ 320–340 K, which slowly increased with x. The M(T) behavior in the magnetic ordering region indicated a nonuniform ground state, due possibly to the competition of ferromagnetic and antiferromagnetic interactions. The increase in the saturation magnetic moment with x can be described by a simple model of the binary bonds in La_{1 − x} Pb _x MnO₃.     

Phase transformations and magnetotransport properties of the Pr0.5Sr0.5Co1 ? xMnxO3 system

The structural, magnetic, and magnetotransport properties of Pr_0.5Sr_0.5Co_{1 − x} Mn _x O₃ (x < 0.65) perovskites are studied by magnetization and electrical conductivity measurements in magnetic fields up to 14 T and by neutron diffraction. In the manganese concentration range x < 0.5 and T = 300 K, the crystal structure is described by monoclinic space group I2/a; at x > 0.5, it is described by orthorhombic space group Imma. When the temperature decreases, a structural transformation without changing the symmetry takes place in all compounds. This transformation is caused by an active role of the inner shells of the praseodymium ion in chemical bond formation. The substitution of manganese for cobalt breaks a long-range ferromagnetic order near x ≈ 0.25, and a metal-dielectric transition occurs at x ≈ 0.15. The negative magnetoresistance is found to be maximal near a critical manganese concentration, where a long-range magnetic order is broken; it reaches 95% in a field of 14 T at T = 10 K for x = 0.2. An unusual dielectric magnetic state with a small spontaneous magnetic moment and a sharp transition into a paramagnetic state at T > 200 K is revealed in the concentration range 0.30 ≤ x ≤ 0.65 in spite of the absence of coherent magnetic neutron scattering. A model is proposed to explain the behavior of the magnetic properties in this phase.     

A study of the microstructure of La1 − x Ca x MnO3 (x = 0.5, 0.8) solid solutions

HREM and XPD methods are used to study the microstructure of La_{1 − x} Ca _x MnO₃ perovskite-like oxides synthesized by pyrolysis of polymer-salt compositions. The XPD data show that the samples studied are single-phase solid solutions. Morphological transitions are observed in series of samples depending on the substitution parameter x. At 0 ≤ x ≤ 0.4 the samples can be characterized by rhombic symmetry (space group Pnmb); at 0.5 ≤ x ≤ 0.8 the symmetry increases to the tetragonal space group I4/mmm; at 0.9 ≤ x ≤ 1 the symmetry lowers to the monoclinic space group P1121. Heating of samples with x = 0.5 and 0.8 up to 1200°C in air does not lead to noticeable changes in the sample structure, which indicates their high thermal stability. When the La_0.2Ca_0.8MnO₃ sample is heated to 1100°C in vacuum nanocrystalline states with particle disintegration into microphases of different structures form because of a partial decomposition of the solid solution. As a result, a system of Mn₃O₄ nanoparticles appears, which is coherently bound with the perovskite phase of a defective structure.     

Morphotropic phase boundary, weak ferromagnetism, and strong piezoelectric effect in Bi1 ? xCaxFeO3 ? x/2 compounds

The crystal structure and magnetic and piezoelectric properties of the Bi_{1 − x} Ca _x FeO_{3 − x/2} system (x ≤ 0.2) are studied. The crystal-structure transformations occur in the following sequence: rhombohedral (R3c) polar phase (x ≤ 0.06) → modulated polar phase (0.07 ≤ x ≤ 0.1) → modulated antipolar phase (0.11 ≤ x ≤ 0.14). The modulated polar and antipolar phases are weakly ferromagnetic with a spontaneous magnetization of 0.25 G cm³/g (x = 0.09). In the polar weak ferromagnet with x = 0.09, a uniform piezoelec- tric response 2.5 times stronger than in the initial BiFeO₃ compound is detected by the piezoelectric force microscopy.     

Zero-field μSR study of ErBa2Cu3Ox for various oxygen contentx

Results from zero-field μSR experiments are presented, performed on the high-T _c compounds ErBa₂Cu₃O_x for various oxygen contentx with 6≤x≤7 at temperatures between 40 mK and 300 K. The aim was to study the magnetic ordering behavior of the Cu moments and the Er moments, and its interplay with superconductivity.     

Magnetic structure of Ce<Subscript>2</Subscript>Fe<Subscript>17 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The magnetic structure of intermetallic compounds Ce₂Fe_{17 − x} Mn _x (0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms.     

57Fe Mössbauer study of ternary alloy systems Fe(Sb1−x Te x )2 for 0.5≤x≤1.0 at 4.2K

Summary We report on low-temperature (4.2 K)⁵⁷Fe M?ssbauer studies of the ternary alloy system Fe(Sb_1−x Te _x )₂ for 0.5≤x≤1.0. The M?ssbauer spectra are electric-quadrupole doublets for all the specimens, indicating a non-magnetic character. The quadrupole splitting decreases with the increase in tellurium concentration. FeTe₂ has also been studied in external magnetic fields up to 6T. These experiments show that the electric-field gradient in this alloy is negative and has an asymmetry parameter of η ≈0.7. Paper presented at the ICAME-95, Rimini, 10–16 September 1995.     

Studies on electrical switching behavior and optical band gap of amorphous Ge–Te–Sn thin films

Amorphous thin film Ge₁₅Te_85−x Sn _x (1≤x≤5) and Ge₁₇Te_83−x Sn _x (1≤x≤4) switching devices have been deposited in sandwich geometry using a flash evaporation technique, with aluminum as the top and bottom electrodes. Electrical switching studies indicate that these films exhibit memory type electrical switching behavior. The switching fields for both the series of samples have been found to decrease with increase in Sn concentration, which confirms that the metallicity effect on switching fields/voltages, commonly seen in bulk glassy chalcogenides, is valid in amorphous chalcogenide thin films also. In addition, there is no manifestation of rigidity percolation in the composition dependence of switching fields of Ge₁₅Te_85−x Sn _x and Ge₁₇Te_83−x Sn _x amorphous thin film samples. The observed composition dependence of switching fields of amorphous Ge₁₅Te_85−x Sn _x and Ge₁₇Te_83−x Sn _x thin films has been understood on the basis of Chemically Ordered Network model. The optical band gap for these samples, calculated from the absorption spectra, has been found to exhibit a decreasing trend with increasing Sn concentration, which is consistent with the composition dependence of switching fields.     

Magnetic phases in Pr0.5Sr0.5Mn1 ? xCoxO3 (x ≤ 0.5) solid solutions

The magnetic and magnetotransport properties of Pr_0.5Sr_0.5Mn_{1 − x} Co _x O₃ (x ≤ 0.5) solid solutions have been investigated using neutron diffraction methods. The magnetization and electrical conductivity have been measured in magnetic fields up to 140 kOe. It has been established that, during cooling in the temperature range from 160 to 110 K, the compounds of compositions with a cobalt content x ≤ 0.07 undergo a structural phase transition from the high-temperature ferromagnetic phase to the antiferromagnetic phase. A further substitution of cobalt for manganese leads to a stabilization of the inhomogeneous dielectric ferromagnetic state, whereas a state of the cluster spin-glass type has been revealed in compositions with x = 0.15 and 0.20. At x ≥ 0.25, a new magnetic phase with a Curie temperature up to 210 K is formed as a result of the magnetic interaction between manganese and cobalt ions. A magnetic phase diagram of the system under investigation has been constructed.