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The rare-earth chromates (RECrO$_3$) and manganites (REMnO$_3$) where, RE = Eu, Y, Dy, Ho, Gd are constantly under scrutiny in search of room temperature magnetoelectric multiferroics. However, the artefacts and undesirable signal in some of the measurements pose a severe challenge in confirming the ferroelectric (FE) phase, especially in reference to pyroelectric current measurement technique. In this regard, we propose a simple modified approach to pyroelectric current measurement named as 4-segment thermal cycling protocol. This protocol assists in isolating the elusive, irreversible thermally stimulated current from the currents associated with spontaneous and reversible nature of the electric polarization in FE phase. In order to explain working principle of the protocol, we have compared simulated response of two hypothetical materials; an FE material free of space charges and a paraelectric material possessing only space charges. Further, we experimentally verify these new protocols in a single crystal of prototype ferroelectric material, Glycine Phosphite. This report primarily focuses on detailed investigation of ferroelectricity using the proposed protocol in two polycrystalline materials, HoCrO$_3$ and DyFe$_{0.5}$Mn$_{0.5}$O$_3$ where, the former has been reported to be multiferroic earlier. Our elaborative and careful approach to pyroelectric studies expound on the absence of reversible spontaneous electric polarization at temperature ranges tested in both, HoCrO$_3$ and DyFe$_{0.5}$Mn$_{0.5}$O$_3$., 13 pages, 6 figures

We study the electronic structure of single-crystal ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$, a non-charge-ordered mixed-valent semiconductor which exhibits a glassy magnetic ground state. We use the techniques of soft x-ray photoemission, hard x-ray photoemission, x-ray absorption, and resonant photoemission spectroscopy to investigate the occupied and unoccupied electronic states of ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Core level photoemission and x-ray absorption spectroscopy allow us to determine the valence states of Tb, Sr, and Mn ions in ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Model charge transfer multiplet calculations of core level photoemission and x-ray absorption spectra are employed to separate out the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ states and confirm their relative concentrations. Resonant photoemission spectroscopy across the Mn $2p\text{\ensuremath{-}}3d$ threshold shows clear resonant enhancement of the Mn $3d$ partial density of states and two-hole correlation satellites. A Cini-Sawatzky analysis gives on-site Coulomb energy ${U}_{dd}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}5.5\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n}$ states and ${U}_{pd}$ = 0.7 $\mathrm{eV}\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n+1}{\underline{L}}^{1}$ states. The O $1s\text{\ensuremath{-}}2p$ resonant photoemission is used to identify the O $2p$ two-hole correlation satellite which provides ${U}_{pp}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}3.4\ifmmode\pm\else\textpm\fi{}0.2$ eV for the O $2p$ states. Valence band photoemission indicates a small-gap semiconductor ($l100$ meV) consistent with electrical transport measurements. The estimated electronic structure parameters of the on-site Coulomb energies, in combination with the charge transfer energy and the hybridization strength obtained from the model calculations, indicate that ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ is a strongly correlated charge transfer type semiconductor.

PVDF exhibits ferroelectric, pyroelectric, and dielectric properties as a function of its unique crystalline phases, namely α, β, γ, δ, and e. Of these, the β crystalline phase shows unique electrical and mechanical properties due to its highly ordered crystalline lamellae and is of industrial interest. Electrospinning is a unique technique to produce long flawless fibers for various applications. In this study, several MgTiO3–PVDF composites were prepared by the electrospinning and solution-casting methods. The objective of this was to examine the combined effect of a popular, low-loss ceramic dielectric like MgTiO3 and a high-dielectric polymer like PVDF in a new architecture. The effect of the filler dispersion on the microstructure, phase transition, and mechanical and electrical properties of the MgTiO3/PVDF composites was investigated in the frequency range of 100 Hz–100 MHz and at 10 GHz. The dynamic mechanical properties of the composites (1–100 Hz) have also been examined. These polymer composites composed of highly crystalline PVDF nanofibers and MgTiO3 appear to have promising dielectric properties distinctly different from their constituent components.

ErFe0.55Mn0.45O3 single crystal shows canted antiferromagnetic ordering below 365 K with weak ferromagnetic moment along c axis. On cooling, the magnetic moment is completely suppressed at a certain temperature due to Er and Fe/Mn sublattice compensation, below which negative magnetization is observed. The compensation and negative magnetization temperatures are much higher than those in other orthoferrite systems. There is a spin reorientation transition from Γ 4 ( G x , A y , F z ) to Γ 1 ( A x , G y , C z ) structure at 255 K along c axis which is not seen along a and b axes. The spin reorientation is tunable with applied magnetic field and is completely suppressed at sufficiently high magnetic field. The behavior is explained by spin configuration and net magnetization orientation of individual Er and Fe/Mn sublattices. The proposed model is further validated by measurements using ’training’ protocol.

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

The perovskite ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ shows two anomalies in its magnetic susceptibility at ${T}_{N}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}257$ K and ${T}_{\mathrm{SR}}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}190$ K which are, respectively, the antiferromagnetic and spin-reorientation transition that occur in the Fe/Cr sublattice. Magnetic susceptibility of this compound reveals canonical signatures of a Griffiths-like phase: a negative deviation from the ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron-diffraction data analysis confirms two spin-reorientation transitions in this compound. The first one from ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) to ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${\mathrm{A}}_{x}, {\mathrm{F}}_{y}, {\mathrm{G}}_{z}$) occurs at ${T}_{N}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}257$ K and a second one from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${\mathrm{A}}_{x}, {\mathrm{F}}_{y}, {\mathrm{G}}_{z}$) to ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) at ${T}_{\mathrm{SR}}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}190$ K in the $Pnma$ space-group setting. The ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) structure is stable down to 7.7 K, leading to an ordered moment of 3.34(1) ${\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Fe}}^{3+}({\mathrm{Cr}}^{3+}$). In addition to the long-range magnetic order, experimental indication of diffuse magnetism is observed in neutron-diffraction data at 7.7 K. Tb develops a ferromagnetic component along the $z$ axis at 20 K. Thermal conductivity and spin-phonon coupling of ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ studied through Raman spectroscopy are also presented in the paper. The magnetic anomalies at ${T}_{N}$ and ${T}_{\mathrm{SR}}$ do not appear in the thermal conductivity of ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$, which appears to be robust up to 9 T. On the other hand, they are revealed in the temperature dependence of full-width-at-half-maximum curves derived from Raman intensities. An antiferromagnetic structure with $\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\downarrow}$ arrangement of Fe/Cr spins is found as the ground state through first-principles energy calculations, supporting the experimentally determined magnetic structure at 7.7 K. The spin-resolved total and partial density of states show that ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ is insulating with a band gap of $\ensuremath{\sim}0.12$ (2.4) eV within GGA ($\mathrm{GGA}+U$) functionals.

This qualitative study examines why Bernice Sandler's role was significant in achieving gender equality in education, and the role she played in the enactment of Title IX legislation, which changed the face of American education. A historical overview of the development of women's higher education is provided and evaluated in order to describe the context of gender discrimination. Gender has been an important tool of oppression of women for centuries. In that aspect, no country has been an exception, including the United States. Like everywhere else, in America as well, the socio-cultural norms and gender roles expectations hindered women from achieving a full education. The potential barriers to women's higher education, as well as the potential outcomes of these marginalizations, were explored in order to gain a more in-depth understanding of this study. Women faced innumerable socially constructed barriers that constrained their educational development. Women's proper role was considered to be a mother, and her proper place was the home. Everything else was considered beyond the normal gender role definitions. But fortunately, there were few early voices that propagated the idea of the importance of giving higher education for women. As a result, women's higher education has gone through various forms, and types of institutions. Female seminaries, women's colleges, co-education and so on, before it spread to all colleges and universities. Even though by the middle of the twentieth century, women have gained broader access to education, but in certain areas, discrimination was still rampant. For example, especially in medicine, law, and business women's entry was restricted through various measures, such as the quota system, which used to limit the number of women being admitted. In the academic workplace, female faculties were more often not promoted or given tenure. Bernice Sandler's activism led to the passing of the Title IX legislation. By mandating to treat all students equally in all aspects of the education, especially in areas regarding admissions, recruitment, financial assistance, etc., in all federally funded institutions, Title IX eliminated all such practices, creating a more gender-equitable environment in education. Most importantly, it was Sandler's almost single-handed initiative that set things in motion and led to changing the educational landscape.

Magnetic measurements on oriented single crystals of Ho 0.5 Dy 0.5 FeO 3 grown using optical floating zone furnace provide evidence for two spin reorientations of Fe 3 + magnetic sublattice viz., Γ 4 → Γ 1 → Γ 2 at temperatures T SR 1 = 49 K and T SR 2 = 26 K . As magnetic field along c axis increases, the sample resumes Γ 4 spin configuration and a large field is likely to disrupt the spin reorientation process. It is evident from isothermal magnetization along c axis that field induced Γ 1 → Γ 4 transition is feasible within the intermediate temperature range of T SR 1 - T SR 2 and can be triggered at a critical field. Such magnetic behavior is better understood as a consequence of anisotropic effective field, modified by the application of external magnetic field.

Despite numerous attempts of electron doping in different manganites (RMnO3, R = rare earth), successful reports are scarce in the literature till date. In this paper, we have synthesized a series of phase-pure electron doped multiferroic compound Sc1-xZrxMnO3 (x = 0, 0.05, 0.1, and 0.2) and evaluated the effect of doping on structural properties, oxidation states of cations, DC magnetization, heat capacity, resistivity, dielectric behaviour and ferroelectricity in the material. The presence of Zr4+ and mixed valence state of Mn comprising of Mn2+ and Mn3+ ions are confirmed using X-ray photoelectron spectroscopy. All these samples exhibit antiferromagnetic ordering; as Zr4+ content increases, antiferromagnetic ordering gradually diminishes while shifting to low temperatures. Additionally, ferromagnetic-like interaction develops in doped systems which gives rise to hysteresis in isothermal magnetization loops with greatly enhanced magnetization in comparison to pure antiferromagnetic nature of x = 0 i.e. ScMnO3. Interestingly, even with zero magnetic moment of Sc3+, Schottky-like anomaly is observed at 5 K in heat capacity data of samples with x = 0.1 and 0.2, a result that we attribute to the highly resistive nature of doped samples. Moreover, while measuring ferroelectric hysteresis loops, we observe a significant reduction of leakage current in doped sample (x = 0.2) compared to pure ScMnO3. Additionally, the compound x = 0.2 shows improved dielectric and ferroelectric behaviour. It is proposed that doping of Zr4+ compensates for the cation deficiency and consequently eliminates the inherent oxygen vacancies by charge compensation. (C) 2017 Elsevier B.V. All rights reserved.

Structural phase transition in half doped compound (CH3)(2)NH2]Mn0.5Ni0.5(HCOO)(3) is investigated. Differential scanning calorimetry data indicated this to be a distinct transition with enthalpy 465.6 J/mol. Powder X-ray diffraction at different temperature shows structural phase transition from trigonal R -3c to monoclinic Cc through co -existing mixed phase. Based on the experimental results, a phase diagram has been proposed. This phase transition is confirmed to be of first order nature by specific heat measurement. Entropy change and latent heat of the phase transition are also calculated from specific heat which are found to be 2.53 J/mol-K and 412 J/mol respectively.

(CH3)(2)NH2]Mn0.5Ni0.5(HCOO)(3) is prepared via solvothermal method. Phase purity and crystal structures are determined at room temperature using powder X-ray diffraction. Temperature variation of magnetization and isothermal field variation of magnetization indicate antiferromagnetic ordering with weak ferromagnetism. This is possibly induced by spin canting. Thermally activated relaxation is observed which is attributed to ordering of dimethylamine cation. This is associated with first order improper antiferroelectric transition. Temperature dependence of polarization and its spontaneity has been confirmed from pyroelectric current measurements. Effect of electric ordering is clearly reflected in impedance spectroscopy data. Two regions are distinct above and below electric ordering temperature which are demarcated by the magnitude of resistance and capacitance of equivalent circuit model and activation energy. Co-existence of magnetic and electric ordering at low temperature is a signature of multiferroic phase.

Traditionally, lead and heavy metal containing inorganic oxides dominate the area of ferroelectricity. Although, recently, lightweight non-toxic organic ferroelectrics have emerged as excellent alternatives, achieving higher temperature up to which the ferroelectric phase can persist has remained a challenge. Moreover, only a few of those are single-component molecular ferroelectrics and were discovered upon revisiting their crystal structures. Here we report a novel phenanthroimidazole derivative, which not only displays notable spontaneous and highly stable remnant polarizations with a low coercive field but also retains its ferroelectric phase up to a record-high temperature of ∼521 K. Subsequently, the crystal undergoes phase transition to form non-polar and centrosymmetric polymorphs, the first study of its kind in a single-component ferroelectric crystal. Moreover, the compound exhibits a significantly high thermal stability. Given the excellent figures-of-merit for ferroelectricity, this material is likely to find potential applications in microelectronic devices pertaining to non-volatile memory.

Implementing topological insulators as elementary units in quantum technologies requires a comprehensive understanding of the dephasing mechanisms governing the surface carriers in these materials, which impose a practical limit to the applicability of these materials in such technologies requiring phase coherent transport. To investigate this, we have performed magnetoresistance (MR) and conductance fluctuations (CF) measurements in both exfoliated and molecular beam epitaxy grown samples. The phase breaking length (${l}_{\ensuremath{\phi}}$) obtained from MR shows a saturation below sample dependent characteristic temperatures, consistent with that obtained from CF measurements. We have systematically eliminated several factors that may lead to such behavior of ${l}_{\ensuremath{\phi}}$ in the context of TIs, such as finite size effect, thermalization, spin-orbit coupling length, spin-flip scattering, and surface-bulk coupling. Our work indicates the need to identify an alternative source of dephasing that dominates at low $T$ in topological insulators, causing saturation in the phase breaking length and time.

One of the unique features of Dirac Fermions is pseudo-diffusive transport by evanescent modes at low Fermi energies when the disorder is low. At higher Fermi energies i.e. carrier densities, the electrical transport is diffusive in nature and the propagation occurs via plane-waves. In this study, we report the detection of such evanescent modes in the surface states of topological insulator through 1/f noise. While signatures of pseudo-diffusive transport have been seen experimentally in graphene, such behavior is yet to be observed explicitly in any other system with a Dirac dispersion. To probe this, we have studied 1/f noise in topological insulators as a function of gate-voltage, and temperature. Our results show a non-monotonic behavior in 1=f noise as the Fermi energy is varied, suggesting a crossover from pseudo-diffusive to diffusive transport regime in mesoscopic topological insulators. The temperature dependence of noise points towards conductance fluctuations from quantum interference as the dominant source of the noise in these samples., 5 pages, 4 figures

It is well known that in double perovskites, the degree of cation ordering plays a very important role in determining the intrinsic magnetic properties. Therefore, in order to distinguish between the intrinsic properties and the disordered cation driven magnetic properties, we have grown ordered and disordered epitaxial thin films of Lu2MnNiO6 (LMNO) using two different cubic substrates (0 0 1)-LaAlO3 and (0 0 1)-SrTiO3 (LAO and STO respectively) by pulsed laser deposition (PLD) method. It is found that both LMNO films grow in monoclinic crystal symmetry and possess two out-of-plane domains (1 1 0) and (0 0 1). Moreover, various in-plane rotations of these domains give rise to a total of six in-plane twin variants. The films show dominant ferromagnetic nature. Due to good lattice matching with LAO, LMNO/LAO films are well-ordered and exhibit a sharp ferromagnetic to paramagnetic transition at TC = 38 K, whereas, the large lattice mismatch with STO resulted in disordered LMNO/STO films and TC is lowered to 34 K. The value of maximum magnetization (MS, at 70 kOe) in disordered LMNO/STO (MS = 2.4 μB/f.u.) is almost half of that in the ordered LMNO/LAO (MS = 4.0 μB/f.u.). Interestingly, the well-ordered LMNO/LAO films show memory effect and relaxation of magnetization in the entire temperature range below TC. This is in conformance to the intrinsic glassy magnetic nature of LMNO.

We have carried out dielectric and transport measurements in NdFe1-xMnxO3 (0 ≤ x ≤ 1) series of compounds and studied the variation of activation energy due to a change in Mn concentration. Despite similar ionic radii in Mn(3+) and Fe(3+), large variation is observed in the lattice parameters and a crossover from dynamic to static Jahn-Teller distortion is discernible. The Fe/Mn-O-Fe/Mn bond angle on the ab plane shows an anomalous change with doping. With an increase in the Mn content, the bond angle decreases until x = 0.6; beyond this, it starts rising until x = 0.8 and again falls after that. A similar trend is observed in activation energies estimated from both transport and dielectric relaxation by assuming a small polaron hopping (SPH) model. Impedance spectroscopy measurements delineate grain and grain boundary contributions separately both of which follow the SPH model. Frequency variation of the dielectric constant is in agreement with the modified Debye law from which relaxation dispersion is estimated.

The diverse properties of two-dimensional materials have been utilized in a variety of architecture to fabricate high quality electronic circuit elements. Here we demonstrate a generic method to control hysteresis and stable memory effect in Van der Waals hybrids with a floating gate as the base layer. The floating gate can be charged with a global back gate-voltage, which it can retain in a stable manner. Such devices can provide a very high, leakage-free effective gate-voltage on the field-effect transistors due to effective capacitance amplification, which also leads to reduced input power requirements on electronic devices. The capacitance amplification factor of ∼10 can be further enhanced by increasing the area of the floating gate. We have exploited this method to achieve highly durable memory action multiple genre of ultra-thin 2D channels, including graphene, MoS2, and topological insulators at room temperature.

A key feature of topological insulators (TI) is symplectic symmetry of the Hamiltonian which changes to unitary when time reversal symmetry is lifted and the topological phase transition occurs. However, such a crossover has never been explicitly observed, by directly probing the symmetry class of the Hamiltonian. In this report, we have probed the symmetry class of topological insulators by measuring the mesoscopic conductance fluctuations in the TI Bi$_{1.6}$Sb$_{0:4}$Te$_2$Se, which shows an exact factor of two reduction on application of a magnetic field due to crossover from symplectic to unitary symmetry classes. The reduction provides an unambiguous proof that the fluctuations arise from the universal conductance fluctuations (UCF), due to quantum interference and persists from T = 22 mK to 4.2 K. We have also compared the phase breaking length (l$_\phi$) extracted from both magneto-conductivity and UCF which agree well within a factor of two in the entire temperature and gate voltage range. Our experiment confirms UCF as the major source of fluctuations in mesoscopic disordered topological insulators, and the intrinsic preservation of time reversal symmetry in these systems., Comment: 6 pages, 4 figures

The emergence of exchange bias effect in Fe

Magnetization reversal and glassy phase in Tb0.7Sr0.3MnO3 are reported. Polycrystalline samples of Tb0.7Sr0.3MnO3 are prepared by solid-state synthesis. This material crystallizes in orthorhombic Pbnm space group with lattice parameters: a = 5.471(1)A, b = 7.608(2)A, and c = 5.398(2)A. Field-cooled/zero field-cooled magnetization measurements show two magnetic transitions, one at 40 K and another at 8 K. The transition at 40 K is due to magnetic ordering of Mn while that at 8 K arises due to Tb ordering. Low field-cooled measurements reveal magnetization reversal at low temperature. The temperature at which this occurs increases with decrease in field strength. The observed magnetization reversal is attributed to the competition between interacting Mn (3 d) and Tb (4 f) magnetic sublattices which makes the system ferrimagnetic. The glassy magnetic behavior below 50 K and absence of long-range order in Tb0.7Sr0.3MnO3 is confirmed through ac susceptibility studies.

Double perovskite R2NiMnO6 (R=Pr, Nd, Tb, Ho and Y) composites are prepared via solid state synthesis or nitrate route. Isothermal magnetic entropy change ( Δ S M ( T , H ) ) and relative cooling power (RCP) for all systems are calculated and compared. All of them possess relatively high values of Δ S M ( T , H ) and RCP as compared to many perovskite and double perovskite systems reported previously. Ho2NiMnO6 has the highest value for | Δ S M ( T , H ) | and RCP as 8.4 JKg − 1 K − 1 at 70 kOe and 59.18 J Kg−1 at 20 kOe respectively. This study highlights the potential of magnetocaloric refrigerant materials at low temperature.

Magnetic and dielectric properties of the double perovskite Ho2NiMnO6 are reported. The compound is synthesized by nitrate route and is found to crystallize in monoclinic P2(1)/n space group. Lattice parameters obtained by refining powder x-ray diffraction data are; a = 5.218(2)angstrom, b = 5.543(2)angstrom, c = 7.480(3)angstrom and the monoclinic angle i beta = 90.18 degrees(4). A phase transition is observed at T-C = 86 K in the temperature-dependent magnetization curve, M(T). The inverse magnetic susceptibility, (1/chi(T)) fits reasonably well with modified Curie-Weiss law by incorporating the paramagnetic response of Ho3+. 1/chi(T) manifests as an upward deviation from ideal Curie-Weiss behaviour well above the ferromagnetic transition. Signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible when one subtracts the Ho3+ paramagnetic contribution from total susceptibility and does the power-law analysis. The magnetic hysteresis at 2 K gives the maximum value of magnetization M-max approximate to 15 mu(B)/f. u. at 50 kOe. Field-derivative of magnetization at 2 K shows discontinuities which indicates the existence of metamagnetic transitions in this compound. This needs to be probed further. Out of the two dielectric relaxations observed, the one at low temperature may be attributed to phononic frequencies and that at higher temperature may be due to Maxwell-Wagner relaxation. A correlation between magnetic and lattice degrees of freedom is plausible since the anomaly in dielectric constant coincides with T-C.

We report the detailed experimental characteristics of LuMn0.5Fe0.5O3 synthesized by the wet chemical method and proclaim it as a new member of the multiferroic family. The compound stabilizes in P63cm crystal symmetry. It exhibits a spin re-orientation transition at TSR and an antiferromagnetic transition at TN. In addition, our magnetization vs. temperature data reveals an extra broad maximum close to room temperature; unseen in earlier studies. By invoking the compatible nature of the magnetic exchange path in P63cm symmetry, we have argued that the origin lies in the intraplane short-range spin ordering. Heat capacity is measured and analysed to elucidate the magnetic entropy. Though long-range antiferromagnetic ordering vanishes at TN ∼ 103 K, we find the experimental magnetic entropy calculated till 200 K is less by a significant amount from the value of theoretical spin randomization magnetic entropy; further supporting the existence of spin ordering beyond TN and even above 200 K. While the specif...

Single crystals of Tb0.5Sr0.5MnO3 were grown in an optical float zone furnace and their magnetic and thermodynamic properties were studied. Temperature dependent DC magnetization measurements at different fields show strong irreversibility below the magnetic anomaly at 44 K. The upward deviation from ideal CW behavior well above the transition temperature and its field independent nature are signatures of non-Griffiths phase. The origin non-Griffiths phase owe to competition between the antiferromagnetic and ferromagnetic Mn3+ Mn4+ interactions mediated through intervening oxygen. Further, 44 K transition is confirmed as a magnetic glassy transition. The estimated dynamical spin flip time (tau(o)=2.11(3) x10(-14) s) and zv(9.3(2)) values fall into the range of typical spin-glass systems. Detailed memory and temperature cycling relaxation measurements were performed and support the Hierarchical relmtation model. Low-temperature specific heat data displays a linear term, identifying the glassy magnetic phase contribution.

The electronic structure of double perovskite Pr2MnNiO6 is studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 2+ and 4+ states respectively. Using charge transfer multiplet analysis of Ni and Mn 2p XPS spectra, we find charge transfer energies {\Delta} of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the atomic values of 8.00 and 3.00 respectively thereby indicating the covalent nature of the system. The O 1s edge absorption spectra reveal a band gap of 0.9 eV which is comparable to the value obtained from first principle calculations for U-J >= 2 eV. The density of states clearly reveal a strong p-d type charge transfer character of the system, with band gap proportional to average charge transfer energy of Ni2+ and Mn4+ ions., Comment: 18 pages, 9 figures

Multiferroic materials are characterized by simultaneous magnetic and ferroelectric ordering making them good candidates for magneto-electrical applications. We conducted thermal expansion and magnetostriction measurements in magnetic fields up to 14 T on perovskitic GdMnO3 by highresolution capacitive dilatometry in an effort to determine all longitudinal and transversal components of the magnetostriction tensor. Below the ordering temperature T (N) = 42 K, i.e., within the different complex (incommensurate or complex) antiferromagnetic phases, lattice distortions of up to 100 ppm have been found. Although no change of the lattice symmetry occurs, the measurements reveal strong magneto-structural phenomena, especially in the incommensurate sinusoidal antiferromagnetic phase. A strong anisotropy of the magnetoelastic properties was found, in good agreement with the type and propagation vector of the magnetic structure. We demonstrate that our capacitive dilatometry can detect lattice expansion effects and changes of the dielectric permittivity simultaneously because the sample is housed inside the capacitor. A separation of both effects is possible by shielding the sample. Dielectric transitions could be detected by this method and compared to the critical values of H and T in the magnetic phase diagram. Dielectric changes measured at 1 kHz excitation frequency are detected in GdMnO3 at about 180 K, and between 10 K and 25 K in the canted antiferromagnetic structure which is characterized by a complex magnetic order on both the Gd- and Mn-sites.

We report on the single crystal growth of 50% Sr and Y doped multiferroic DyMnO3 using optical floating zone technique. A comparison of the effect of growth ambience and of chemical substitution on the crystal structure of DyMnO3 is attempted. It is observed that DyMnO3 adopts Pm3m cubic structure with 50% Sr doping whereas with 50% Y doping, the crystal structure is hexagonal P6(3)cm. Orthorhombic Pnma structure is adopted by DyMnO3 when grown in air, whereas hexagonal P6(3)cm structure is obtained when grown under the ambience of argon. The structural polymorphism is discussed in terms of difference in ionic sizes of Sr, Y and Dy, comparable Gibbs free energies and coordination schemes of surrounding oxygens for hexagonal and orthorhombic structures of DyMnO3. (C) 2012 Elsevier B.V. All rights reserved.

Lithium L-Ascorbate dihydrate (LLA) is a new metal organic nonlinear optical crystal belonging to the saccharide family. Single crystals of LLA were grown from aqueous solution. Solubility of the crystal has a positive temperature coefficient facilitating growth by slow cooling. Rietveld refinement was used to confirm the phase formation. The crystal has prismatic habit with (010), (001) and (10-1) prominent faces. Thermal analysis shows that the crystal is stable up to 102 degrees C. Transmission spectrum of the crystal extends from 302 nm to 1600 nm. Dielectric spectroscopic analysis revealed Cole Cole behaviour and prominent piezoelectric resonance peaks were observed in the range of 100-200 kHz. Second harmonic generation (SHG) conversion efficiency of up to 2.56 times that of a phase matched KDP crystal was achieved when the (010) plate of LLA single crystal was rotated about the +ve c axis, by 9.4 degrees in the clockwise direction. We also observed SHG conical sections which were attributed to noncollinear phase matching. The observation of the third conical section suggests very high birefringence and large nonlinear coefficients. A detailed study of surface laser damage showed that the crystal has high multiple damage thresholds of 9.7 GW cm(-2) and 42 GW cm(-2) at 1064 nm and 532 nm radiation respectively. (C) 2012 Elsevier B.V. All rights reserved.

Single crystals of lithium D-isoascorbate monohydrate (LDAM), (C6H7O6Li center dot H2O), are grown by a solution growth method. The crystal structure of LDAM is solved using single crystal X-ray diffraction. The space group is orthorhombic P2(1)2(1)2(1) with four formula units per unit cell and lattice parameters a = 7.7836(3) angstrom, b = 8.7456(3) angstrom, and c = 11.0368(4) angstrom. Solubility of the material in water is determined thermogravimetrically and found to have a positive temperature coefficient of solubility. Large optical quality single crystals are subsequently grown from aqueous solution by a slow cooling method. The crystal has a bulky prismatic habit and among the prominent faces the c face appears as the only principal morphological face. The crystal exhibits a (010) cleavage. Dielectric spectroscopy reveals a nearly Debye type Cole-Cole behavior with anisotropy in relaxation. Optical transmission range is found to be from 300 to 1400 nm. The principal refractive indices of this biaxial crystal, measured using Brewster's angle method, at wavelengths 405, 543, and 632.8 nm, show high dispersion. The crystal is negative biaxial with 2V(z) = 107.8 degrees (405 nm) and belongs to the Hobden class 3. Theoretically generated type 1 and type 2 second order phase matching curves match very well with the experimental results. The second-order nonlinear coefficient d(14) was determined to be 7 x 10(-13) m/V. For the optimum phase matching direction (type 2), the second-order effective nonlinear coefficient and the walk off angle are determined to be 0.84 times d(14) and 3.5 degrees respectively. The crystal possesses high multiple surface damage thresholds of 18 GW/cm(2) and 8 GW/cm(2) at laser wavelengths 1064 and 532 nm, respectively.

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO$_3$ studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at $T^\mathrm{Fe/Mn}_N \approx$ 295~K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, $T^\mathrm{Fe/Mn}_{SR} \approx$ 26~K where a spin-reorientation transition occurs in the Fe/Mn sublattice and $T^\mathrm{R}_N \approx$ 2~K where Tb-ordering starts to manifest. At 295~K, the magnetic structure of the Fe/Mn sublattice in TbFe$_{0.5}$Mn$_{0.5}$O$_3$ belongs to the irreducible representation $\Gamma_4$ ($G_xA_yF_z$ or $Pb'n'm$). A mixed-domain structure of ($\Gamma_1 + \Gamma_4$) is found at 250~K which remains stable down to the spin re-orientation transition at $T^\mathrm{Fe/Mn}_{SR}\approx$ 26~K. Below 26~K and above 250~K, the majority phase ($> 80\%$) is that of $\Gamma_4$. Below 10~K the high-temperature phase $\Gamma_4$ remains stable till 2~K. At 2~K, Tb develops a magnetic moment value of 0.6(2)~$\mu_\mathrm{B}/$f.u. and orders long-range in $F_z$ compatible with the $\Gamma_4$ representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe$_{0.5}$Mn$_{0.5}$O$_3$ and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-$Q$ region of the neutron diffraction patterns at $T < T^\mathrm{Fe/Mn}_{SR}$. These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe$_{0.5}$Mn$_{0.5}$O$_3$., Comment: 16 pages, 7 figures, Accepted to J. Appl. Phys., 2016

Large single crystals of Sodium D-isoacsorbate monohydrate and Lithium L-ascorbate dehydrate were grown using solution growth technique. Dielectric constant and dielectric loss were monitored as a function of frequency at different temperatures. These are typically characterized by strong resonance peaks. The piezoelectric coefficients d(31), elastic coefficient (S-11) and electromechanical coupling coefficient (k(31)) were estimated by resonance-antiresonance method. The temperature dependence of the resonance-peaks frequencies was studied.

Critical behavior of double perovskite Y2NiMnO6 near the second-order ferromagnetic transition is studied. Scaling exponents calculated frommodified Arrot plots are confirmed by Kouvel-Fisher method and satisfy the Widom's scaling relation. The exponents do not follow any conventional theoretical models.beta values areconsistent with 3D-Ising model while delta conformsto TCMF and gamma valueclosely relates to the 3D-Heisenberg model. Critical exponents are compared with similar R2NiMnO6 double perovskites which shows that a decrease in size of R ion changes exponents from mean-field to the 3D-Ising model.

Here, we report the dielectric, impedance and transport studies of non-charge-ordered magnetic glass, Tb0.5Sr0.5MnO3 single crystals. The temperature-and frequency-dependent real (epsilon') and imaginary (epsilon'' or tan delta) parts of the dielectric constant display large frequency dispersion. The colossal dielectric constant observed (approximate to 3000) above 100K is considered extrinsic. The activation energy of thermally activated relaxation is calculated using the Arrhenius law. Interestingly, two relaxation regions, each with different activation energies (E-a) are clearly evident, one occurring above and the other below the glassy magnetic transition temperature (T-g = 44K). E-a relates to the electron hopping between Mn3+ and Mn4+ ions and the origin of dielectric dispersion. Ea in the glassy region is lower than that in paramagnetic region due to a lower energy spent in hopping between frozen spins. Bulk capacitance and resistivity derived from impedance measurements reveal anomalies around T-g. Electrical transport data between 60 and 300K shows insulating behavior and the calculated E-a is in good agreement with the value obtained from dielectric measurements. Although, these results cannot be interpreted in terms of magneto-electric coupling, the correlation observed between magnetic and electronic states of the system is significant. Copyright (C) EPLA, 2016

Highly non-linear I–V characteristics and apparent colossal electro-resistance were observed in non-charge ordered manganite Tb 0.5 Sr 0.5 MnO 3 single crystal in low temperature transport measurements. Significant changes were noticed in top surface temperature of the sample as compared to its base while passing current at low temperature. By analyzing these variations, we realize that the change in surface temperature ( Δ T sur ) is too small to have caused by the strong negative differential resistance. A more accurate estimation of change in the sample temperature was made by back-calculating the sample temperature from the temperature variation of resistance (R–T) data ( Δ T cal ) , which was found to be higher than Δ T sur . This result indicates that there are large thermal gradients across the sample. The experimentally derived Δ T cal is validated with the help of a simple theoretical model and estimation of Joule heating. Pulse measurements realize substantial reduction in Joule heating. With decrease in sample thickness, Joule heating effect is found to be reduced. Our studies reveal that Joule heating plays a major role in the nonlinear electrical response of Tb0.5Sr0.5MnO3. By careful management of the duty cycle and pulse current I–V measurements, Joule heating can be mitigated to a large extent.

An organic nonlinear optical material, namely glucuronic acid gamma-lactone or glucuronolactone, was crystallized from aqueous solution. Crystals of large dimensions and full morphology were obtained by slow-cooling method in a custom-built solution growth setup. CHN analysis and X-ray diffraction confirmed the phase formation in the grown crystal. High-resolution XRD studies followed by Rietveld refinement yielded accurate lattice parameters which compared well with the reported values. UV-Vis spectrum recorded for a b-plate of 2 mm thickness revealed the low UV-cutoff at 250 nm. Dielectric constant and dielectric loss were monitored as a function of frequency. Piezoelectric resonance peaks were observed in the range 0.2-1.5 MHz which are dependent on the plate thickness. The temperature dependence of the resonance peak frequency was studied. Piezoelectric coefficients were estimated by resonance-antiresonance method.

D-Isoascorbic acid (C6H8O6) crystals belonging to the monoclinic space group P2(1) are grown from aqueous solution employing slow cooling technique. The grown crystals possess blocky morphology with (100) (010) and (001) prominent faces. Thermal analysis shows that the crystals are stable up to 162 degrees C and decompose immediately after melting. The optical transmission lower cutoff is determined to be 300 nm. The Kleinman conjecture, applicable to second-order nonlinear coefficients, was violated as the optical transmission was dependent on the state of the incident light polarization. The principal dielectric frame of the crystal was determined using conoscopy and is found to be rotated about the crystallographic b-axis. Non-collinear SHG rings up to second order were observed which helped to locate phase matching directions. The second harmonic conversion efficiency of the crystal is measured to be 3x that of a KDP crystal by both single crystal phase matching and Kurtz powder techniques. Surface laser damage thresholds at 1064 and 532 nm are determined to be 9.7 and 4.2 GW/cm(2), respectively.

Bulk, transparent organic nonlinear optical (NLO) single-crystals of imidazolium L-Ascorbate (ImLA) were grown using slow-evaporation. Crystal structure was determined by single crystal X-ray diffraction analysis. Preliminary linear optical measurements through UV-Visible and infrared spectroscopy revealed good optical transmittance and a low near-UV cutoff wavelength at 256 nm. Kurtz and Perry powder test revealed that ImLA is a phase-matchable NLO material with a second harmonic generation (SHG) efficiency of 1.2 times larger than that of standard KH2PO4 (KDP). Laser damage thresholds were determined for ImLA.

A new double perovskite Ho2FeMnO6 was grown by nitrate route. Temperature dependent dielectric response was recorded at different frequencies. Relaxor-like-behavior is observed whose activation energy was calculated using Arrhenius equation. The dispersion is very small at room temperature. The Nyquist plot over a broad frequency range at room temperature provides evidence for the presence of three relaxations from sample electrode interface, grain boundary and grain. The corresponding values of resistance and capacitance were calculated from the equivalent circuit model analysis of the Nyquist plot.

The double perovskite Y2NiMnO6 displays ferromagnetic transition at T-c approximate to 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (Ms) and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P2(1)/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T-c). Pyrocurrent measurements register a current flow with onset near T-c and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong topological insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in field-effect transistors (FET) of mechanically exfoliated Bi1.6Sb0.4Te2Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter gamma(H) as low as approximate to 10(-4), but it increases rapidly when channel thickness exceeds similar to 1 mu m. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.

We present an extensive study on magnetic and transport properties of La(0.85)Sr(0.15)CoO(3) single crystals grown by a float zone method to address the issue of phase separation versus spin-glass (SG) behavior. The dc magnetization study reveals a kink in field-cooled magnetization, and the peak in the zero-field-cooling curve shifts to lower temperature at modest dc fields, indicating the SG magnetic phase. The ac susceptibility study exhibits a considerable frequency-dependent peak shift (similar to 4 K) and a time-dependent memory effect below the freezing temperature. In addition, the characteristic time scale tau(0) estimated from the frequency-dependent ac susceptibility measurement is found to be similar to 10(-13) s, which matches well with typical values observed in canonical SG systems. The transport relaxation study evidently demonstrates the time-dependent glassy phenomena. In essence, all our experimental results corroborate the existence of SG behavior in La(0.85)Sr(0.15)CoO(3) single crystals.

The magnetic behavior of La0.85Sr0.15CoO3 single crystals and polycrystals has been subjected to a controversial debate for the last several years; while some groups show evidence for phase separation, others show spin-glass (SG) behavior. Here, we present a comprehensive investigation of the structural, ac susceptibility, and dc magnetization properties of La0.85Sr0.15CoO3 single crystals grown by float zone method. The structural analysis of XRD data by Rietveld refinement reveals the single crystallographic phase. The ac susceptibility results exhibit a frequency dependent peak shift (∼2 K) and time-dependent memory effect below the freezing temperature. The characteristic time scale τo calculated from this peak shift is found to be of ∼10−13 s which matches very well with typical values observed for a SG system. Further, the peak shift of the zero-field-cooling curves to lower temperature at higher dc fields is well described by the well-known de Almeida Thouless line, a characteristic of SG behavior. Thus, all our experimental findings confirm the existence of SG behavior in La0.85Sr0.15CoO3 single crystals.

The emergence of exchange bias effect in Fe3O4 thin films has been since attributed to the presence of anti phase boundary (APB) growth defects despite lack of direct experimental evidence. In the present report, APB induced anomalous weak ferromagnetism and exchange bias property of single-phase antiferromagnetic (AFM) system LuMn0.5Fe0.5O3 (LMFO) is discussed and Fe-57 Mossbauer spectroscopy and high resolution transmission electron microscopy (HRTEM) measurements are used to probe the origin of the observed effect. In addition to the sextet component corresponding to the long range AFM ordering, the measured Mossbauer spectra reveal the presence of a small component (10%-12%) near zero velocity with unusually small internal field. This indicates the presence of APB defects. From micro structural investigations using HRTEM, presence of APB type defects and dislocations are confirmed. In addition to the exchange bias effect, upon field cooling, hysteresis loop exhibits large vertical shift due to strong pinning effect of the APB. Finally we further annealed the optimally sintered sample LMFO and studied the evolution of defects, and their influence on weak ferromagnetism and exchange bias properties. Our present experimental findings may pave the way in creating new functionalities in materials using APB-type growth defects.