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Large size single crystals of potassium L-ascorbate monohydrate (KLAM), (KC6H7O6.H2O) are grown using solution growth technique by lowering the temperature at the rate of 0.24 {\deg}C/h, where water was used as solvent. The structure of KLAM was solved by single crystal XRD. KLAM crystallizes in non-centrosymmetric, monoclinic, P21 space group with lattice parameters a = 7.030(5) {\AA}, b = 8.811(5) {\AA}, c = 7.638(5) {\AA} and \b{eta} = 114.891(5){\deg}. The crystal grows with bulky morphology in all three directions having (100), (-100), (-110), (0-1-1), (0-11), (001) and (00-1) prominent faces. TGA and DSC measurements show that KLAM is stable up to 80 {\deg}C. The crystal shows good optical transparency with a lower cut off as low as 297 nm. Second harmonic conversion efficiency measured on powder sample is 3.5 times that of potassium dihydrogen phosphate (KDP). Phase matching (PM) is observed on a plate of the KLAM. Noncollinear phase matching rings are also observed near the PM directions which help to identify the locus of PM directions. Presence of noncollinear SHG rings up to third order suggests large birefringence and nonlinear optical coefficients. Laser damage threshold value of the crystal is found to be 3.07 GW/cm2, at 1064 nm in 100 direction., Comment: 13 pages

Frequency-dependent and temperature-dependent dielectric measurements are performed on double perovskite Tb$_2$NiMnO$_6$. The real ($\epsilon_1$) and imaginary ($\epsilon_2$) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from bulk, grain boundaries and the sample-electrode interfaces respectively. The temperature and frequency variation of $\epsilon_1$ and $\epsilon_2$ are successfully simulated by a $RC$ circuit model. The complex plane of impedance, $Z'$-$Z"$, is simulated using a series network with a resistor $R$ and a constant phase element. Through the analysis of frequency-dependent dielectric constant using modified-Debye model, different relaxation regimes are identified. Temperature dependence of dc conductivity also presents a clear change in slope at, $T^*$. Interestingly, $T^*$ compares with the temperature at which an anomaly occurs in the phonon modes and the Griffiths temperature for this compound. The components $R$ and $C$ corresponding to the bulk and the parameter $\alpha$ from modified-Debye fit tend support to this hypothesis. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is marked., Comment: Accepted in Europhysics Letters

We have investigated the influence of Fe-excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (Tc) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field Hc1, it is inferred that excess of Fe suppresses superconductivity. The linear and non-linear responses of the ac-susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe-excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity drho/dT in the temperature range Tc < T < Ta with Ta being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above Tc in the sample with higher amount of Fe suggests a disorder driven electronic localization., Comment: 7 pages

The floating-zone method with different growth ambiances has been used to selectively obtain hexagonal or orthorhombic DyMnO$_{3}$ single crystals. The crystals were characterized by X-ray powder diffraction of ground specimen and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetisation, and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO$_{3}$ shows magnetic ordering of Mn$^{3+}$ (S =2) spins on a triangular Mn lattice at $T^{\mathrm {Mn}}_{N}$ = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy$^{3+}$ (S=9/2) spins. At $T^{\mathrm {Dy}}_{N}$ = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO$_{3}$ display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn$^{3+}$ spins at $T^{\mathrm {Mn}}_N$ = 39 K, a {\textit{lock--in}} transition at $T_{\mathrm {lock-in}}$ = 16 K and a second antiferromagnetic transition at $T^{\mathrm {Dy}}_N$ = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4$f-4f$ and 4$f-3d$ couplings., Comment: 15 figures

Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.15 < x 0.5 have been studied in low temperature regime. The resistivity in the ferromagnetic insulating (FMI) phase for x < 0.3 has an activated character. The dependence of the activation gap Delta on doping x has been determined and the critical concentration for the zero-temperature metal-insulator transition was determined as x_{c} ~ 0.33. For a metallic sample with x=0.42, a conventional electron-electron (e-e) scattering term proportional T^{2} is found in the low-temperature electrical resistivity, although the Kadowaki-Woods ratio is found to be much larger for this manganite than for a normal metal. For a metallic sample with x=0.5, a resistivity minimum is observed for x= 0.5. The effect is attributed to weak localization and can be described by a negative T^{1/2} weak-localization contribution to resistivity for a disordered three-dimensional electron system. The specific heat data have been fitted to contributions from free electrons (gamma), spin excitations (beta_{3/2}), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. The value of gamma is larger than for normal metals, which is ascribed to magnetic ordering effects involving Nd. Also, the Schottky-like anomaly appears broadened and weakened suggesting inhomogeneous molecular fields at the Nd-sites., Comment: 14 pages, 8 figures

High resolution topographic images obtained by scanning tunneling microscope in the insulating state of Pr0.68Pb0.32MnO3 single crystals showed regular stripe-like or zigzag patterns on a width scale of 0.4 - 0.5 nm confirming a high temperature polaronic state. Spectroscopic studies revealed inhomogeneous maps of zero-bias conductance with small patches of metallic clusters on length scale of 2 - 3 nm only within a narrow temperature range close to the metal-insulator transition. The results give a direct observation of polarons in the insulating state, phase separation of nanometer-scale metallic clusters in the paramagnetic metallic state, and a homogeneous ferromagnetic state.

InAs_{x}Sb_{1-x} alloys show a strong bowing in the energy gap, the energy gap of the alloy can be less than the gap of the two parent compounds. We demonstrate that a consequence of this alloying is a systematic degradation in the sharpness of the absorption edge. The alloy disorder induced band-tail (Urbach tail) characteristics are quantitatively studied for InAs_{0.05}Sb_{0.95}., Comment: 3 figures

Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs in the absence of magnetoresistance (MR). Measurements of electroresistance (ER) and current induced resistivity switching have been performed in the ferromagnetic insulating state of a single crystal manganite of composition Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic insulating state is realized for temperatures, T <~ 130 K. The colossal electroresistance, arising from a strongly nonlinear dependence of resistivity ($\rho$) on current density (j), attains a large value ($\approx 100%$) in the ferromagnetic insulating state. The severity of this nonlinear behavior of resistivity at high current densities is progressively enhanced with decreasing temperature, resulting ultimately, in a regime of negative differential resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with the build-up of the ER however, is a collapse of the MR to a small value (< 20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled in the ferromagnetic insulating phase of manganites. We establish that, the behavior of ferromagnetic insulating phase is distinct from the ferromagnetic metallic (FMM) phase as well as the charge ordered insulating (COI) phase, which are the two commonly realized ground state phases of manganites., Comment: 24 pages (RevTeX4 preprint), 8 figures, submitted to PRB

The critical properties at the ferromagnetic - paramagnetic transition have been analysed from data of static magnetization measurements on single crystals of Pr1-xPbxMnO3, for x = 0.23 and x = 0.30. In Pr1-xPbxMnO3 the ferromagnetic ordering and the metal-insulator transition do not coincide in parts of the phase diagram. The crystal with x = 0.23 is a ferromagnetic insulator with Curie temperature Tc = 173 K, while the crystal with x =0.30 has Tc = 198 K and remains metallic up to a metal-insulator transition temperature Tmi = 235 K. The dc magnetization measurements were carried out in the field range from 0 to 5 T for an interval in the critical temperature range Tc+_10 K corresponding to a reduced temperature interval 0.003 < epsilon < 0.6. The exponents beta for spontaneous magnetization, gamma for the initial susceptibility above Tc and delta for the critical magnetization isotherm at Tc were obtained by static scaling analysis from modified Arrott plots and by the Kouvel Fisher method for the insulating crystal with composition x = 0.23. The data are well described by critical exponents similar to those expected for the Heisenberg universality class relevant for conventional isotropic magnets Systematic deviations from scaling in the data for the metallic crystal with composition x = 0.30 are demonstrated from effective critical exponents near the assumed ordering transition. The unconventional magnetic ordering in this system indicates the presence of frustrated magnetic couplings that suppresses magnetic ordering and lowers the transition temperature., Comment: 9 double column pages, 14 figures. 1 table

The structure of Nd$_{1-x}$Pb$_{x}$MnO$_{3}$ crystals is determined by single crystal X-ray diffraction. Substitution of Pb at the Nd site results in structural phase change from tetragonal (x = 0.25) to cubic (x = 0.37). These changes are attributed to the progressive removal of inter-octahedral tilting and minimization of the octahedral distortion leading to a higher symmetry as doping concentration increases. While the unit cell volume of tetragonal structure ($\it{P4/mmm}$) is comparable to that of parent NdMnO$_{3}$, the volume of cubic unit cell ($\it{Pm\bar{3}m}$) is doubled. Electron diffraction patterns support these results and rule out the possibility of twinning. Changes in transport properties as a function of temperature at different doping levels are in accordance with the observed structural changes. It is noticed that $\it{T_{c}}$ and $\it{T_{MI}}$ increase with x., Comment: 8 figures, Communicated to Journal of Materials Chemistry

Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in the temperature range around T_C (Curie temperature) which embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the T_C =156.47 +/- 0.06 K and the critical exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547 +/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The exponent values are very close to those expected for the universality class of 3D Heisenberg ferromagnets with short-range interactions., Comment: 19 pages, including 6 figures

Single crystals of Nd_{1-x}Pb_{x}MnO_{3} with x=0.2 are grown by high temperature solution growth technique using PbO-PbF_{2} flux. Magnetization studies on the samples show a transition to a ferromagnetic state below T_c ~ 125 K and the resistivity measurements show it to be an insulator throughout the temperature range 50 - 300 K. Electron Paramagnetic Resonance studies have been performed for T > T_{C} with a view to comparing the results with those on metallic ferromagnetic manganites. The temperature dependence of various parameters like g-value, linewidth and intensity has been studied in the temperature range 150 - 300 K. It is found that they behave in a manner similar to that exhibited by metallic ferromagnetic manganites., Comment: 8 pages, 4 figures

Variable temperature scanning tunneling microscopy/spectroscopy studies on single crystals and epitaxial thin films of hole-doped manganites, which show colossal magnetoresistance, have been done. We have investigated the variation of the density of states, at and near the Fermi energy ($E_f$), as a function of temperature. Simple calculations have been carried out, to find out the effect of temperature on the tunneling spectra and extract the variation of density of states with temperature, from the observed data. We also report here, atomic resolution images, on the single crystals and larger range images showing the growth patterns on thin films. Our investigation shows unambiguously that there is a rapid variation in density of states for temperatures near the Curie temperature ($T_c$). While for temperatures below $T_c$, a finite DOS is observed at $E_f$, for temperatures near $T_c$ a hard gap opens up in the density of states near $E_f$. For temperatures much higher than $T_c$, this gap most likely gives way to a soft gap. The observed hard gap for temperatures near $T_c$, is somewhat higher than the transport gap for all the materials. For different materials, we find that the magnitude of the hard gap decreases as the $T_c$ of the material increases and eventually, for materials with a $T_c$ close to 400 K, the value of the gap approaches zero., Comment: 9 pages RevTeX, 12 postscript figures, 1 table included in text, submitted to Physical Review B