Uniaxial and hydrostatic pressure effects in alpha-RuCl3 single crystals via thermal-expansion measurements

We present high-resolution thermal-expansion and specific-heat measurements of single crystalline alpha-RuCl3. An extremely hysteretic structural transition expanding over 100 K is observed by thermal- expansion along both crystallographic axes, which we attribute to a change of stacking sequence of the RuCl3 layers. Three magnetic transitions are observed, which we link to the different stacking sequences. Using our data and thermodynamic relations, we derive the uniaxial and hydrostatic pressure derivatives of all three magnetic transitions. Our results demonstrate that magnetic order should be totally suppressed by very moderate pressures of 0.3 GPa to 0.9 GPa. Finally, we discuss why our results differ from recent hydrostatic pressure measurements and suggest a possible route to reaching the spin-liquid state in alpha-RuCl3.Comment: 6 pages, 3 figure

Magnetization, crystal structure and anisotropic thermal expansion of single-crystal SrEr2O4

The magnetization, crystal structure, and thermal expansion of a nearly stoichiometric Sr$_{1.04(3)}$Er$_{2.09(6)}$O$_{4.00(1)}$ single crystal have been studied by PPMS measurements and in-house and high-resolution synchrotron X-ray powder diffraction. No evidence was detected for any structural phase transitions even up to 500 K. The average thermal expansions of lattice constants and unit-cell volume are consistent with the first-order Gr\"uneisen approximations taking into account only the phonon contributions for an insulator, displaying an anisotropic character along the crystallographic \emph{a}, \emph{b}, and \emph{c} axes. Our magnetization measurements indicate that obvious magnetic frustration appears below $\sim$15 K, and antiferromagnetic correlations may persist up to 300 K.Comment: 6 pages, 5 figure, 2 table

Intermultiplet transitions and magnetic long-range order in Sm-based pyrochlores

We present bulk and neutron scattering measurements performed on the isotopically enriched $^{154}\mathrm{Sm_2Ti_2O_7}$ and $^{154}\mathrm{Sm_2Sn_2O_7}$ samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to determine the crystalline electric field (CEF) level scheme, which includes transitions between the ground-state and first excited $J$ multiplets of the $\mathrm{Sm}^{3+}$ ion. To further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental DC-susceptibility measured in low applied magnetic fields. It is demonstrated that the inclusion of intermultiplet transitions in the CEF analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomaly is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly inferred.Comment: 13 pages, 10 Figure

Magnetic Excitations in the Ground State of Yb2Ti2O7\mathrm{Yb_2Ti_2O_7}

We report an extensive study on the zero field ground state of a powder sample of the pyrochlore $\mathrm{Yb_2Ti_2O_7}$. A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic order develops below $T_\mathrm{c}$ with a magnetic moment of $0.87(2)\mu_\mathrm{B}$. High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at $\sim0.6$ meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.Comment: 11 pages, 9 figures, Phys. Rev. B. (accepted

Magnetic and structural transitions in La0.4_{0.4}Na0.6_{0.6}Fe2_2As2_2 single crystals

La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single crystal x-ray and neutron diffraction. La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals show a structural phase transition from a high temperature tetragonal phase to a low-temperature orthorhombic phase at T$_s$\,=\,125\,K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the \emph{a} direction with an ordered moment of 0.7(1)\,$\mu_{\textup{B}}$ at \emph{T}\,=\,5 K. The low temperature stripe antiferromagnetic structure is the same as that in other \emph{A}Fe$_{2}$As$_{2}$ (\emph{A}\,=\,Ca, Sr, Ba) compounds. La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ provides a new material platform for the study of iron-based superconductors where the electron-hole asymmetry could be studied by simply varying La/Na ratio.Comment: 9 pages, 7 figures, to appear in Physical Review

Ингибирование асфальтосмолопарафиновых отложений водонефтяных эмульсий нефти Верхне-Салатского месторождения

High quality thin films of TbMnO3 were grown by pulsed laser deposition on orthorhombicYAlO(3) (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04 degrees and 0.2 degrees for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO3. (C) 2011 Elsevier B.V. All rights reserved

Macrocyclic Tetramers—Structural Investigation of Peptide-Peptoid Hybrids

Outstanding affinity and specificity are the main characteristics of peptides, rendering them interesting compounds for basic and medicinal research. However, their biological applicability is limited due to fast proteolytic degradation. The use of mimetic peptoids overcomes this disadvantage, though they lack stereochemical information at the α-carbon. Hybrids composed of amino acids and peptoid monomers combine the unique properties of both parent classes. Rigidification of the backbone increases the affinity towards various targets. However, only little is known about the spatial structure of such constrained hybrids. The determination of the three-dimensional structure is a key step for the identification of new targets as well as the rational design of bioactive compounds. Herein, we report the synthesis and the structural elucidation of novel tetrameric macrocycles. Measurements were taken in solid and solution states with the help of X-ray scattering and NMR spectroscopy. The investigations made will help to find diverse applications for this new, promising compound class

PENGARUH PENAMBAHAN POTONGAN KARUNG PLASTIK SEBAGAI BAHAN CAMPURAN UNTUK MEMPERKUAT TIMBUNAN TANAH LEMPUNG

Terbatasnya lahan untuk pembangunan yang diperlukan mengakibatkan tidak dapat dihindarinya pembangunan di atas tanah lempung seperti tanah yang ada di Indonesia. Oleh karena itu, sangat penting untuk mencampurkan bahan tambahan sebagai campuran ke dalam tanah lempung tersebut untuk meningkatkan kualitas daya dukung tanah pada tanah lempung. Karena banyaknya permintaan karung plastik, limbah karung plastik menjadi semakin banyak, maka peneliti mencoba untuk memanfaatkan serat karung plastik tersebut sebagai bahan campuran pada tanah lempung benda uji. Dengan mencampurkan potongan serat karung plastik ke dalam tanah lempung, diharapkan tanah lempung campuran serat karung plastik tersebut dapat meningkatkan kepadatan tanah dan dapat memperkuat kuat geser tanah. Studi ini meliputi, studi literatur dan penelitian di Laboratorium Mekanika Tanah ITN Malang pada tanggal 7 April – 19 Juli 2019. Tanah benda uji dalam penelitian ini berasal dari Ds. Argotirto, Kec. Sumbermanjing Wetan, Kab. Malang dan bahan campuran potongan serat karung plastik sepanjang ≥ 1cm - ≤ 3cm dengan variasi kadar campuran; 1%, 1,5%, 2%, 2,5%, 3% dari berat total tanah saat kadar air optimum. Penelitian ini meliputi pengujian sifat fisik dan sifat teknis. Pengujian sifat fisik meliputi; Kadar Air Tanah Asli (w), Berat Jenis (Gs), Analisa Saringan, Analisa Hidrometer, Uji Plastisitas (LL, PL, SL), Tingkat Pengembangan, dan Tingkat Keaktifan (Activity). Pengujian sifat teknis meliputi; Compaction Standard dan Modified, Triaxial UU, dan Unconfined Compression, masing-masing pengujian terdiri dari 3 sampel. Dengan dibantu uji hipotesis data untuk mengetahui adanya pengaruh atau tidak adanya pengaruh dalam pengujian tanah lempung campuran serat karung plastik tersebut. Berdasarkan hasil pengujian, tanah benda uji penelitian tersebut termasuk dalam tanah MH (Lanau anorganik atau pasir halus diatomac, atau lanau diatomac, lanau yang elastis). Nilai hasil pengujian campuran serat karung plastik cenderung meningkat dibandingkan tanah tanpa campuran. Nilai tertinggi untuk bahan timbunan mendapatkan prosentase kadar campuran serat karung plastik sebanyak 3% pada pengujian Modified Compaction sebesar; 1,528g/cm3, dengan nilai kadar air (w) sebesar; 26,89%. Pada pengujian Triaxial UU, mendapatkan nilai Kohesi (c) sebesar; 0,350kg/cm², dengan nilai Sudut Geser (φ) sebesar; 6,277 pada kadar campuran 3%. Dan pada pengujian Unconfined Compression, mendapatkan nilai Tegangan Normal (qu) sebesar; 0,681kgf/cm2 pada kadar campuran 1%