Irreversibility of the magnetic state of Tm1 xTbxCo2 revealed by specific heat, electrical resistivity, and neutron diffraction measurements

The substitution of Tb for Tm in the Laves phase compound Tm Co2 leads to appearance of a magnetic moment on the Co atoms through the metamagnetic transition in the itinerant d -electron subsystem and gives rise to long-range ferrimagnetic order in Tm1-x Tbx Co2 at x≥0.15. The magnetic state of the compound Tm0.9 Tb0.1 Co2, i.e., just below the critical Tb concentration, is characterized by the presence of large regions with short-range magnetic order and localized spin fluctuations (LSFs) induced in the Co 3d -electron subsystem by the fluctuating f-d exchange due to the Tm-Tb substitution. The peculiar magnetic state of this compound is strongly influenced by an external magnetic field which produces a first-order magnetic phase transition to a long-range ferrimagnetic state with the magnetic moment on the Co atoms up to (0.7-0.8) μB. This field-induced transition in Tm0.9 Tb0.1 Co2 is found to be irreversible. It is accompanied by a giant and irreversible reduction of the electrical resistivity (Δρ ρ∼-45%), specific heat (by about 3.7 times at 2 K), and intensity of magnetic neutron scattering. Such behavior is associated with the field-induced metamagnetic transition in the itinerant d -electron subsystem mediated by the f-d exchange. Significantly enhanced values of the residual resistivity and the coefficient γ of the T -linear contribution to the specific heat in the compound with x=0.1 as well as their unusual behavior with temperature and under application of the magnetic field is ascribed to the presence of LSF. © 2006 The American Physical Society.This work was partly performed at the Swiss Spallation Neutron Source SINQ, Paul Scherrer Institute (PSI), Villigen, Switzerland. This work was supported by the Russian Foundation for Basic Research (Grant No. 04-02-96060) and by the Swiss National Science Foundation (SCOPES Project No. IB7420-110849)

Magnetic Structures of Some Multiferroics

We studied crystal and magnetic structures of some composite and single-phase multiferroics: (x)MFe2O4 + (1-x)BaTiO3, Ni3-yCoyV2O8, and Bi0.9Ba0.1Fe0.9Ti0.1O3. Composite multiferroics (x)MFe2O4 + (1-x)BaTiO3 with x = (0.2; 0.3; 0.4) and M = (Ni, Co) have ferrimagnetic structure, which is described by the propagation vector k = 0. Oxides Ni3-yCoyV2O8 with y = (0.1; 0.3; 0.5) possess a modulated magnetic structure, described by the vector k = (δ, 0, 0), where δ = 0.283 and 0.348 at 7.4 K for y = 0.1 and 0.5, respectively. In the Bi0.9Ba0.1Fe0.9Ti0.1O3 multiferroic a magnetic order is destroyed at 600 K and the Fe-ion magnetic moment decreases from µ = 3.46(5) μB at 300 K to zero at 600 K

Uneven time series forecasting using a modified exponential smoothing method

The article is devoted to the problem of forecasting time series with an uneven distribution of observations over time. The exponential smoothing model is used as the basic forecasting model, in which the variable weights of observations decrease exponentially. The exponential smoothing model allows us to take into account the attenuation of the correlation of cross sections of a random process of time series change over time. However, this does not take into account the factors of temporal unevenness of the results of observations and the finiteness of the sample of observations. The article describes a method for predicting an uneven time series based on a modified exponential smoothing model, in which the transition from exponential smoothing to decreasing non-exponential smoothing is carried out. The modified sequence of the weights of the observations is determined by adjusting the classically calculated exponential weights, taking into account the actual irregularity of the observations

Context Free Evolution of Words

Projet MEVALRandom grammars were introduced in computer science, but the study of their thermodynamic and long time behaviour started only recently. In this paper we undertake more detailed study of context free grammars in the supercritical case, that is when the word grows exponentially fast. We study and calculate the statistics of factors for large t, prove the existence of various limiting measures and study relations between them

Study of the process e+e−→3(π+π−) in the c.m. energy range 1.5–2.0 GeV with the CMD-3 detector

AbstractThe cross section of the process e+e−→3(π+π−) has been measured using a data sample of 22 pb−1 collected with the CMD-3 detector at the VEPP-2000 e+e− collider. 7956 signal events are selected in the center-of-mass energy range 1.5–2.0 GeV. The measured cross section exhibits a sharp drop near the pp¯ threshold. A first study of dynamics of six-pion production has been performed

RHEOMETRIC MONITORING OF THE FORMATION OF MILK-PROTEIN BLOBS

This paper presents the results of the theoretical and experimental studies of newly designed devices, namely, the VRSh-1 ball rheometer and the Sgustok-1S dual-range rotary viscometer, for the continuous automatic monitoring of structure formation processes in milk-protein blobs. Each type of rheometers is studied to substantiate and select their geometric and kinematic parameters and the shape of measuring elements. It has been shown that the mechanical actions on the structure of milk-protein blobs during the rheometric monitoring of their formation must be minimal to obtain reliable data on their readiness. It has been proven that the monitoring of the formation of blobs by the method of the low-amplitude dynamic oscillations of a ball does not necessitate the measurement of the phase shift of its oscillations, and the total force of the resistance of a strengthening clot to the displacements of a ball inside it should be selected as a control parameter, which is in direct proportion to the amplitude of linear displacements of a ball in a viscoelastic medium (blob). Such a solution simplifies the design of a rheometer and makes it possible to obtain a similar rheogram, which precisely and reliably describes the coagulation of a milk mixture. The possibility of switching the rigidity ranges of force indicators without stopping the electrical drive, the design of which prevents a formed blob from dynamic impacts, thus providing the precision of monitoring and the preservation of the structure of a blob, has been designed for the method a cylinder rotating in a formed blob. The algorithm of the computer approximation of rheometric monitoring results for the formation of milk-protein blobs with the possibility of correcting its consistence at the terminal stage of coagulation is described

Features of Ni Co Ordering in the LiNi1 xCoxPO4 x 0.3, 0.5, 0.7 Crystal Structure

LiNi1 xCoxPO4 x 0.3, 0.5, 0.7 compounds have the olivine structure, space group Pnma, with 3d transition metal ions in the 4c octahedral position. The structural analysis of polycrystalline LiNi1 amp; 8194; amp; 8194;xCoxPO4 x 0.3, 0.5, 0.7 samples is carried out by elastic neutron scattering, and variants of the mutual distribution of nickel and cobalt ions in the 4c position are studied in detail. For the LiNi0.5Co0.5PO4 compound, six options for the mutual distribution of nickel and cobalt ions are proposed. The best description of the neutron diffraction patterns for the compounds with x 0.5 is obtained for two models of the distribution of Ni and Co ions in the sequence Ni Co Ni Co and Co Ni Co Ni, respectively. Nickel ions form planes in the LiNi0.5Co0.5PO4 sample, parallel to ab and alternating with cobalt planes. To describe the neutron diffraction patterns of x 0.3 and x 0.7 compounds, four variants of models for the mutual distribution of Ni and Co ions in the 4c position are proposed. The four versions of the models considered lead to additional structural reflections that are absent in the experimental neutron diffraction patterns. The experimental neutron diffraction patterns of the LiNi0.7Co0.3PO4 and LiNi0.3Co0.7PO4 compounds can best be described using the equiprobable distribution of 3d transition metal ion

Magnetic Structures of the LiNi0.9Co0.1PO4 Crystal

We present the magnetic structures and properties of single crystal and polycrystalline samples LiNi0.9Co0.1PO4 obtained by conventional self f lux LiCl growth from solution and glycerol nitrate methods, respectively. The samples were studied with magnetic property measurement system, X ray and neutron diffraction. A symmetry analysis of possible magnetic structures for the propagation vectors kC 0 and kIC 0, k, 0 was carried out. The magnetic structures in the LiNi0.9Co0.1PO4 single crystal are commensurate kC 0 and incommensurate kIC 0, k, 0 antiferromagnetic orders. The module k is equal 0.10 0.12 reciprocal lattice units at low temperatures. At 7 K, the magnetic moment of the 3d ion is 2.0 amp; 956;B and decreases to zero at 21 K. The temperatures of magnetic phase transitions determined during magnetic property measurements are similar in single crystal and polycrystalline samples. Single crystal neutron diffraction is made it possible to observe some details of the incommensurate structur

Magnetic lock-in phase transition in Tb0.95Er0.05Ni5 driven by low magnetic fields

AbstractThe magnetic properties of a mixed inter-metallic compound, Tb0.95Er0.05Ni5, were investigated using a neutron diffraction method at low temperatures. These compounds were known to have a successive magnetic phase transition from the paramagnetic state at high temperature to a lock-in phase at low temperature through intermediate phases, i.e., PM(paramagnetic)–FM(ferromagnetic)–IC(incommensurate)–L(lock-in) in reverse order of temperature. A meta-magnetic phase transition between an IC phase and a FM phase at 9K was observed with the critical field, HMT~200mT. A new magnetic phase between the new phase (lock-in phase) and an IC phase has been observed. From the field dependence of the Bragg reflections and their satellite peaks at low temperatures (3–12K), weak field driven first-order magnetic phase transitions were recorded at six fixed temperatures. The critical magnetic field decreases exponentially with the temperature. From these experimental results, we obtained a magnetic phase diagram of Tb0.95Er0.05Ni5 at a low temperature region for the first time

Models of Ni and Co ion occupation in LiNi0.5Co0.5PO4 orthophosphate and its magnetic structure

The neutron diffraction, magnetic and heat capacity measurements have been carried out to study the polycrystalline sample LiNi0.5Co0.5PO4 prepared by the glycerol nitrate synthesis method. Models of Ni and Co ion occupation the 4c octahedral position in a crystal structure LiNi0.5Co0.5PO4 are calculated for a paramagnetic state. The best model is the Ni and Co ions occupy the 4c site in Pnma patent space group in sequence Ni Co Ni Co or Co Ni Co Ni. It is shown that nickel ions form ab planes alternating with the planes of cobalt ions in the direction of the c crystallographic axis. At 7 K, an average magnetic moment of 3d ions is equal to 1.90 9 amp; 956;B. The moments are ordering antiferromagnetically and parallel to the bc plane decreasing to zero at 15 K. In the high spin state a temperature dependence of the Ni2 Co2 ion magnetic moment is well described within the 2D Ising model with order parameter amp; 946; 0.198 and N el temperature TN 14.1 1 K, obtained from heat capacity data. This temperature agrees well with Tcr 14.3 2 K, determined with magnetic measurement. Maybe the short range magnetic order exists in LiNi0.5Co0.5PO4 over temperature region 14 16 K, that is confirmed by the maximum on a temperature dependence of the magnetization at 16.1 5