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1.
The magnetic susceptibility of the layered compounds (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2 has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given. 相似文献
2.
Neeraj Khare Ajai K. Gupta G.L. Bhalla 《Journal of Physics and Chemistry of Solids》2005,66(6):949-953
Double layered manganite of La1.4Ca1.6Mn2O7 (DLCMO) was prepared using solid state reaction method and had a metal-insulator transition temperature (TMI) of 125 K. The short range 2D-feerromagnetic ordering (TC2) starts growing when T<168 K and it gets converted into 3D-ferromagnetic ordering (TC1) at 114 K. Low field magnetoresistance (MR) behaviour of the DLCMO was investigated and compared with an infinite layered manganite La0.7Ca0.3MnO3 (LCMO). For DLCMO, in the temperature range between TC1 and TC2, the MR showed a gradual increase with the magnetic field. The observed MR and R-T behaviour of double layered manganite for TC1<T<TC2 has been explained in the frame work of the two phase model [ferromagnetic (FM) domains and paramagnetic (PM) regions] and percolative behaviour of transport in FM-PM mixture. 相似文献
3.
A.S Lagutin J VanackenA Semeno Y BruynseraedeR Suryanarayanan 《Solid State Communications》2003,125(1):7-10
In order to study the mechanism behind the phase separation scenario in the Sm0.15Ca0.85MnO3 compound, magnetization and resistivity measurements have been carried out in pulsed magnetic fields up to 50 T at temperatures 4.2 K<T<200 K. It is found that external magnetic field causes a collapse of a C-type AFM (P21/m) phase resulting in field-induced insulator-metal transition, which is irreversible below T1=75 K. In zero field the content of a G-type phase in the mixed C-G state can vary from 10 to 17% at T=10 K. A set of metastable states with different volume ratios of G-type to C-type phases is observed below T1 depending on the history of the sample. The obtained results indicate that the phase separation plays a dominant role for the electric and the magnetic properties of this material. 相似文献
4.
R. Ortega-Zempoalteca R. Valenzuela 《Journal of magnetism and magnetic materials》2009,321(19):3159-3163
The thermomagnetic behaviour (within the temperature range 553-300 K) for the bulk composite Nd60Fe30Al10 alloy is described in terms of a transition from paramagnetic to superferromagnetic state at T=553 K, followed by a ferromagnetic ordering for T<473 K. For the superferromagnetic regime, the alloy thermomagnetic response was associated to a homogeneous distribution of magnetic clusters with mean magnetic moment and size of 1072 μB and 2.5 nm, respectively. For T<473 K, a pinning model of domain walls described properly the alloy coercivity dependence with temperature, from which the domain wall width and the magnetic anisotropy constant were estimated as being of ≈8 nm and ≈105 J/m3, typical values of hard magnetic phases. Results are supported by microstructural and magnetic domain observations. 相似文献
5.
V.G. Anufriev 《Physics letters. A》1977,64(1):139-140
The temperature dependence of the Cr2O3 EPR spectra is obtained. The linewidth of the EPR is defined by the phonon's modulation of the exchange interactions at T >TN + 4–5 K though at TN < T < TN + 4 K the critical broadening of the EPR in Cr2O3 is determined by fluctuation effects. 相似文献
6.
R.R. Sun X.Y. Qin L.L. Li D. Li J. Zhang Y.S. Zhang C.J. Tang 《Journal of Physics and Chemistry of Solids》2014
The Ruddlesden–Popper (RP) phase compounds (Sr0.95R0.05)3Ti2O7 (R=Er, Y, Dy, Gd, Eu, Sm, Nd and La) were prepared, and their transport and thermoelectric properties were investigated. The results indicate that high-T electrical resistivity ρ (300 K<T<1000 K) increases monotonically with temperature and basically has a relation ρ∝TM, with M varying from 0.91 to 1.92 at temperatures T>~650 K, suggesting acoustic phonon scattering is dominant. At low temperatures (5 K<T<300 K), ρ for (Sr0.95R0.05)3Ti2O7 (R=Nd and La) decreases monotonously with decreasing temperature, whereas ρ for (Sr0.95R0.05)3Ti2O7 (R=Er, Y, Dy, Gd, Eu and Sm) decreases first, and then increases instead as T decreases to a critical temperature Tc. Moreover, electrical conductivity σ∝T1/2 holds at lower temperatures, indicating that the electron–electron interaction caused by the presence of disorder dominates the transport process at the low temperatures. Besides, experiments show that at T<~400 K the lattice thermal conductivity of the doped compounds basically decreases with increase of the atomic mass of dopants. Generally, the figure of merit (ZT) at 1000 K increases first, and then decreases with the increase of the dopants' ionic radius, and the largest ZT is achieved in (Sr0.95Gd0.05)3Ti2O7 mainly owing to its lower lattice thermal conductivity. 相似文献
7.
The heat capacity of (C6H11NH3) CuCl3 (CHAC) has been measured for 0.45 < T < 60 K. Three-dimensional ordering is observed at T = 2.214 K. The data in the paramagnetic region can be described by a ferromagnetic Heisenberg linear chain model system with J/k = +45 ± 5K. 相似文献
8.
The sublattice magnetization of the quadratic-layer basal-plane antiferromagnet K2FeF4 has been studied by use of Mössbauer spectroscopy. A distribution of Néel temperatures with a width ~3 K is found at a mean TN = 67.2±0.3 K. For 0.3 < T/TN < 0.99 the sublattice magnetization is described by a power law with critical exponent β = 0.17±0.01. 相似文献
9.
John C. Papaioannou George S. Patermarakis 《Journal of Physics and Chemistry of Solids》2005,66(5):839-844
The frequency dependence of the real (?′) and imaginary (?″) parts of the dielectric constant of polycrystalline hematite (α-Fe2O3) has been investigated in the frequency range 0-100 kHz and the temperature range 190-350 K, in order to reveal experimentally the electron hopping mechanism that takes place during the Morin transition of spin-flip process. The dielectric behaviour is described well by the Debye-type relaxation (α-dispersion) in the temperature regions T<233 K and T>338 K. In the intermediate temperature range 233 K<T<338 K a charge carrier mechanism takes place (electron jump from the O2− ion into one of the magnetic ions Fe3+) which gives rise to the low frequency conductivity and to the Ω-dispersion. The temperature dependence of relaxation time (τ) in the −ln τ vs 103/T plot shows two linear regions. In the first, T<238 K, τ increases with increasing T implying a negative activation energy −0.01 eV, and in the second region T>318 K τ decreases as the temperature increases implying a positive activation energy 0.12 eV. The total reorganization energy (0.12-0.01) 0.11 eV is in agreement with the adiabatic activation energy 0.11 eV given by an ab initio model in the literature. The temperature dependence of the phase shift in the frequencies 1, 5, 10 kHz applied shows clearly an average Morin temperature TMo=284±1 K that is higher than the value of 263 K corresponding to a single crystal due to the size and shape of material grains. 相似文献
10.
Temperature dependence of conduction noise and low field magnetoresistance of layered manganite La1.4Ca1.6Mn2O7 (DLCMO) are reported and compared with the infinite layered manganite La0.7Ca0.3MnO3 (LCMO). The double layered manganite was prepared using standard solid state reaction method and had a metal-insulator transition temperature (TM-I) of 155 K. The temperature dependence of susceptibility showed evolution of ferromagnetic ordering at 168 K. The observed voltage noise spectral density (SV) shows 1/fα type of behaviour at all temperatures from 77 K to 300 K. In the ferromagnetic region (T<168 K), SV/V2 shows two peaks at 164 K and 114 K. The observed two peaks in normalised conduction noise of DLCMO is attributed to the excess noise generated due to setting up of short range 2D-ferromagnetic ordering and long range 3D-ferromagnetic ordering at two different temperatures TC2 and TC1. In temperature range between TC1 and TC2, the magnetoresistance (MR) showed a gradual increase with the magnetic field. The observed MR has been explained in the framework of the two phase model [ferromagnetic (FM) domains and paramagnetic (PM) regions]. 相似文献
11.
G.V. Bazuev A.V. Korolyov T.I. Chupakhina 《Journal of magnetism and magnetic materials》2010,322(5):494-312
Two methods—the solid-phase high-temperature (1300 °C) and the liquid-phase low-temperature (750 °C) routes—were used to synthesize the complex oxide La1.25Sr0.75MnCoO6, which has the structure of rhombohedral perovskite and is characterized by a disordered distribution of Mn and Co in structural sites. It was found by means of X-ray absorption near edge spectroscopy (XANES) at the K-edge that mixed valence states of Co2+/Co3+ and Mn3+/Mn4+, exist in both phases. Measurements of dc magnetization and real (χ′) and imaginary (χ″) parts of the ac susceptibility showed that the magnetic properties of these oxides are determined by a ferromagnetic transition at TC=217 K and a frequency-dependent transition at Tg<100 K. The high frequency dependence of Tg is indicative of the cluster-glass behavior of La1.25Sr0.75MnCoO6 (7 5 0) at T<TC within the ferromagnetic state. 相似文献
12.
J.H.M. Mooy 《Solid State Communications》1981,39(12):1305-1309
Critical behaviour with dimensionality d = 2 has been observed for the 300 K antiferrodistortive phase transition in Al ur6(ClO4)3 and Ga ur6(ClO4)3 by means of the temperature dependence of the ESR parameter D. The systems exhibited d = 2 behaviour in the static critical behaviour for T<Tc?40 K for T>Tc + 40 K. From the ESR data including line width measurements the local order parameter relaxation rate ω1 has been obtained for various temperatures above Tc, with a lowest value of ω1 = 150 MHz at Tc + 15 K 相似文献
13.
Bae Soon Son Sam Jin Kim Younghun Jo Myung-Hwa Jung Bo Wha Lee Chul Sung Kim 《Journal of magnetism and magnetic materials》2008
The sample of FeSc2S4 was prepared by solid reaction method. The crystallographic structure and the magnetic properties of the fabricated compound were investigated by X-ray, and superconducting quantum interference device (SQUID) magnetometer and Mössbauer spectroscopy. The polycrystalline FeSc2S4 confirmed the normal cubic spinel structure (space group Fd3m). The lattice constants a0 and anion parameter u are 10.519 Å and 0.255, respectively. The Mössbauer spectroscopy has been studied for the FeSc2S4 at various temperatures, ranging from 4.2 K to room temperature. The spectra consist of two doublets at 4.2 K while a single line at room temperature. It is noticeable that the Mössbauer spectra of two doublet patterns with large electric quadrupole splitting (ΔEQ) remain over the Néel temperature. Those are interpreted as a result of large electric quadrupole interaction compared to magnetic dipole interaction. The magnetic susceptibility measurements were performed with a SQUID magnetometer for temperatures 2<T<320 K, in external fields up to 5 kOe. Magnetic behavior shows antiferromagnetic behavior and the magnetic superexchange interactions between the Fe ions are weakly antiferromagnetic. The paramagnetic susceptibilities follow Curie–Weiss (CW) law with CW temperature ΘCW=−100 K, and frustration parameter f=−ΘCW/TN is of the order of 1000. We conclude that two sublattices are coupled antiferromagnetically, leading to strong frustration effects. 相似文献
14.
A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La0.67Ba0.33MnO3 materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data (<75 K) can be best fitted in the frame work of Kondo-like spin-dependant scattering, electron-electron and electron-phonon interactions. It has been found that upturn behavior may be attributed to weak spin disorder scattering including both spin polarization and grain boundary tunneling effects, which are the characteristic features of extrinsic magnetoresistance behavior, generally found in nanocrystalline manganites. The variation of electrical resistivity with temperature in the high temperature ferromagnetic metallic part of electrical resistivity (75K<T<TP) has been fitted with grain/domain boundary, electron-electron and magnon scattering mechanisms, while the insulating region (T>TP) of resistivity data has been explained based on adiabatic small polaron hopping mechanism. 相似文献
15.
Magnetization and spin-flip Raman measurements are reported for Cd1?xMnxSe, x = 0.106, at 1.9 < T < 4.2 K and magnetic fields H up to 80 kOe. The high-field results are combined to determine the exchange energy between donor electrons and Mn++ spins, αN0=261±13 meV. Empirical fits to the magnetization data are described. 相似文献
16.
J. Pérez P.J. Silva C.A. Durante-Rincón J. Primera Ferrer J.R. Fermin 《Journal of magnetism and magnetic materials》2008
Electron paramagnetic resonance (EPR) experiments were made in the diluted magnetic semiconductor CuGa1−xMnxTe2, in the temperature range 70<T<300 K. The samples were synthesized by direct fusion of stoichiometric mixtures of the elements, with Mn composition from x=0.0 to 0.25. The EPR spectra were measured as function of temperature, Mn composition, and field orientation. The temperature variation of the resonance field shows a critical point at about 235 K, and is associated with a transition from the ferromagnetic to the superparamagnetic state. The resonance field was also measured as a function of the field angle, and displays a well-defined uniaxial symmetry. This uniaxial field depends on the Mn concentration and is due to tetragonal distortions induced by Mn2+ at Ga sites, and the demagnetizing effects due to formation of ferromagnetism (FM) Mn-clusters. 相似文献
17.
The temperature dependence of the monoclinic lattice constants in the two smectic phases, S1G and S2G, of HxBPA, has been obtained from X-ray diffraction data, in the temperature range 300 K < T < 240 K. The variation of b (unique axis) is consistent with the chain ordering in the S2G phase indicated by Raman and NMR measurements. 相似文献
18.
Magnetic characteristics of SmMn2Ge2 with a layer structure have been studied by magnetization measurements using single crystal. In the sequence of decreasing temperature, ferromagnetism is observed at 196 K ? T ? 348 K, collinear antiferromagnetism becomes stable for 64 K ? T < 196 K and reentrant ferromagnetism appears below 64 K. The appearance of such successive magnetic orderings are attributed to the variation of the shortest Mn-Mn distance due to thermal expansion and the existence of ferromagnetic coupling between the Sm moments in the intralayer which is dominant at low temperatures. 相似文献
19.
Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH3)3NCH2COO·H3AsO4]
The present work reports an experimental investigation on the influence of glycine (NH2CH2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH3)3NCH2COO·H3AsO4. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K<T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities. 相似文献
20.
We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (ρ) in the 1.8-300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T<30 K. The effect of pressure on BaFe2As2 is to shift the onset of the crystallographic transformation down in temperature at the rate of ~−1.04 K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba0.55K0.45)Fe2As2 is to shift the onset of superconductivity to lower temperatures at the rate of ~−0.21 K/kbar. The effect of pressure on CaFe2As2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P<5 kbar. However, higher pressures bring about another phase transformation characterized by reduced-resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (Hc2) data in (Ba0.55K0.45)Fe2As2 and CaFe2As2 are discussed. 相似文献