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1.
P. Schobinger-Papamantellos J. Rodríguez-Carvajal G. Andr K.H.J. Buschow 《Journal of magnetism and magnetic materials》2006,300(2):333-350
We present the temperature magnetic phase diagram of the compound DyFe4Ge2 determined from neutron diffraction data for the entire magnetically ordered regime. DyFe4Ge2 undergoes at a simultaneous structural and magnetic transition of second order (or weakly first order) followed by two subsequent isostructural first-order magnetic transitions at and Tic1=28K: The re-entrant lock-in magnetic phase is stable in the high-temperature range Tic2–TN and in the low-temperature range 1.5 K–Tic1 while the incommensurately modulated magnetic phase is sandwiched in the intermediate range Tic1–Tic2 between the two commensurate phases. The wave vector q2 has a temperature-dependent length with a minimum in the middle of the incommensurate range and corresponds to a multiaxial amplitude modulated phase. Symmetry analysis leads for both propagation vectors in Cmmm to a twofold and fourfold splitting of the tetragonal Dy 2b site and the Fe 8i sites, respectively. The low temperature and the phases correspond to 3D canted magnetic structures described by the irreducible representations (Irreps) Γ2+Γ3 while the high-temperature q1 phase to 2D canted magnetic structures described by a single Irrep Γ2. The Tic2 transition is connected with reorientations of both Fe and Dy moments. 相似文献
2.
P. Schobinger-Papamantellos J. Rodríguez-Carvajal K. H. J. Buschow E. Dooryhee A. N. Fitch 《Journal of magnetism and magnetic materials》2000,210(1-3)
High-quality powder XRD data of the compound ErFe4Ge2 collected in the ESRF beam line BM16, are presented for the entire magnetically ordered regime (TN=44 K). The data analysis reveals the occurrence of a double symmetry breaking at the magnetic transition. This experiment has allowed us to distinguish between structural and magnetic satellites, both present in the neutron patterns, and to demonstrate the interdependence of structural and magnetic transitions. The high-temperature (HT) phase disproportionates by a first-order transition into two distinct phases: P42/mnm (Tc, TN=44 K)→Cmmm (majority LT phase)+Pnnm (minority IT Phase) which coexist in proportions varying with temperature down to 4 K. The phase diagram comprises three temperature regions: (a) the HT range with T>TN for the tetragonal P42/mnm phase; (b) the IT (intermediate temperature) range, 20 K<T<TN, where the two phases coexist in strongly variable proportions and the Pnnm phase reaches its highest concentration (≈31%) around 30 K and (c) the LT (low temperature) range, 1.5–20 K, where the Cmmm phase is dominating (up to 95%). We suggests that this phenomenon is the result of competing magneto-elastic mechanisms involving the Er crystal field anisotropy, the Er–Er, Er–Fe and the Fe–Fe exchange interactions and their coupling with the lattice strains. 相似文献
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4.
Magda B. Fontes Sergey L. Bud'ko Mucio A. Continentino Elisa M. Baggio-Saitovitch 《Physica B: Condensed Matter》1999,270(3-4)
In this work we present a magnetoresistance study on the CeRu2Ge2 compound. We analyze the ρ(T) curves for several applied magnetic fields using the electron–magnon scattering model for a ferromagnetic spin arrangement. From this analysis, the field dependence of the energy gap of the magnon spectrum is obtained. The magnetoresistance ρ(H) at various temperatures arises from a normal metal contribution with an additional scattering mechanism due to electron–magnon interaction. 相似文献
5.
Two sets of crystal field (CF) parameters have been proposed for DyFe2Si2, none of which could provide a simultaneous explanation of the available experimental data, particularly at low temperatures (below 100 K). The set derived from magnetic studies could not even explain the thermal variation of the magnetic specific heat reported in the same work. Although the set of CF parameters, obtained from a fit to the Mossbauer spectra, could provide a fairly good explanation of the thermal variation of the magnetic susceptibilities along the c-axis, it could not explain the observed thermal variation of other reported experimental findings. In the present work, an appraisal of the CF parameters proposed earlier has been done and a set of CF parameters has been derived, which provide a simultaneous explanation of all the available experimental data. The effect of substitution of Ge for Si on the magnetic properties and the magnetic specific heat of DyFe2Si2 has been studied in the framework of one electron crystal field model. The inelastic neutron scattering studies and EPR measurements are required to check the predicted Stark energies and the paramagnetic resonance g-values. 相似文献
6.
Dominik Uhlich 《Journal of luminescence》2008,128(10):1649-1654
This work reports on the phase formation during a solid-state reaction of Eu3+-doped garnets with the general formula A3B2Ge3O12 (A=Ca, Sr and B=Ga, In, Y) and their luminescent properties. It is shown by XRD and DTA/TG experiments that the garnet-phase formation is completed at 1100-1200 °C. Moreover, it turned out that the position of the oxygen to europium charge-transfer band and the intensity of the forbidden 4f-4f transitions of Eu3+ is dependent on the covalent interaction between the Eu3+ activator and the surrounding oxygen anions. The investigated red-emitting luminescent materials show high lumen equivalents and deep red emission at the same time, which makes them attractive for the application in LEDs (light emitting diodes), in particular for near UV-emitting LEDs. 相似文献
7.
D.M. Rajkumar M. Manivel RajaR. Gopalan V. Chandrasekaran 《Journal of magnetism and magnetic materials》2008
Evolution of structure and magnetocaloric properties in ball-milled Gd5Si2Ge2 and Gd5Si2Ge2/0.1 wt% Fe nanostructured powders were investigated. The high-energy ball-milled powders were composed of very fine grains (70–80 nm). Magnetization decreased with milling time due to decrease in the grain size and randomization of the magnetic moments at the surface. The magnetic entropy change (ΔSM) was calculated from the isothermal magnetization curves and a maximum value of 0.45 J/kg K was obtained for 32 h milled Gd5Si2Ge2 alloy powder for a magnetic field change of 2 T while it was still low in Fe-contained alloy powders. The thermo-magnetic measurements revealed that the milled powders display distribution of magnetic transitions, which is desirable for practical magnetic refrigerant to cover a wide temperature span. 相似文献
8.
《Journal of magnetism and magnetic materials》1992,110(3):L259-L260
Magnetic phase transitions in NdRu2Ge2 under external pressure are studied. The (p, T) phase diagram is presented. An additional phase is observed for pressures p ≥ 4.3 kbar. 相似文献
9.
A modified Yafet-Kittle model is applied to investigate the magnetic properties and magnetic phase transition of the intermetallic compound GdMn_2Ge_2. Theoretical analysis and calculation show that there are five possible magnetic structures in GdMn_2Ge_2. Variations of external magnetic field and temperature give rise to the first-order or second-order magnetic transitions from one phase to another. Based on this model, the magnetic curves of GdMn_2Ge_2 single crystals at different temperatures are calculated and a good agreement with experimental data has obtained. Based on the calculation, the H-T magnetic phase diagrams of GdMn_2Ge_2 are depicted. The Gd-Gd, Gd-Mn, intralayer Mn-Mn and interlayer Mn-Mn exchange coupling parameters are estimated. It is shown that, in order to describe the magnetic properties of GdMn_2Ge_2, the lattice constant and temperature dependence of interlayer Mn-Mn exchange interaction must be taken into account. 相似文献
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11.
J.G.S. Duque R. Lora SerranoD.J. Garcia L. BufaicalL.M. Ferreira P.G. PagliusoE. Miranda 《Journal of magnetism and magnetic materials》2011,323(7):954-956
In this work, we have investigated the low temperature magnetic phase diagram of the tetragonal NdRhIn5 and Nd2RhIn8 single crystals by means of temperature and field dependent heat capacity and magnetic susceptibility measurements. These compounds order antiferromagnetically with a Néel temperature (TN) of 11 and 10.7 K for NdRhIn5 and Nd2RhIn8, respectively. The constructed magnetic phase of both compounds are anisotropic and show, as expected, a decrease of TN as a function of the magnetic field for c crystallographic direction. However when the magnetic field is applied along of the c-axis, which is the magnetic easy axis, first-order-like field induced transitions are observed within the antiferromagnetic state. We compare the phase diagrams obtained for NdRhIn5 and Nd2RhIn8 with those for their cubic relative NdIn3. 相似文献
12.
High quality single crystal CaFe4As3 was grown by using the Sn flux method. Unlike layered CaFe2As2, CaFe4As3 crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed at ~90 K and ~27 K, respectively. The high temperature transition is an antiferromagnetic(AF) ordering transition. However, the low temperature transition shows complex properties. It shows a ferromagnetic-like transition when a field is applied along b-axis, while antiferromagnetism-like transition when a field is applied perpendicular to b-axis. These results suggest that the low temperature transition at 27 K is a first-order transition from an AF state to a canted AF state. In addition, the low temperature electron specific heat coefficient reaches as high as 143 mJ/mol·K2, showing a heavy fermion behavior. 相似文献
13.
Liang Zhang Guang-Fu Ji Feng ZhaoChuan-Min Meng Dong-Qing Wei 《Physica B: Condensed Matter》2011,406(3):335-338
Magnesium aluminum spinel (MgAl2O4) is a major constituent of the shallow upper mantle. It is of great geophysical importance to explore its physical properties under high pressure and temperature. The first-principle density functional theory (DFT) with the plane wave along with pseudopotential was employed to obtain the total energy for both Fd3m-MgAl2O4 and F4-3m-MgAl2O4, which was used to generate the Gibbs free energy as a function of temperature and pressure with the quasi-harmonic Debye model. It is found that the phase transition temperature from Fd3m-MgAl2O4 to F4-3m-MgAl2O4 is beyond 452.6 K in the pressure regime studied, which is consistent with the experiment. The phase transition temperature is related to pressure by a linear function, i.e. T=8.05P+452.6, which is the first equation of this kind to describe the phase transition Fd3m→F4-3m. The elastic constants, equation of states and thermodynamic properties of Fd3m-MgAl2O4 are also reported in this paper to make a complete study. 相似文献
14.
Spinel LiMn2O4 active material with high capacity retention 总被引:1,自引:0,他引:1
Xifei Li 《Applied Surface Science》2007,253(21):8592-8596
Heating the mixture of LiMn2O4 and NiO at 650 °C was employed to enhance the cyclability of spinel LiMn2O4. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy analyses implied that a LiNixMn2−xO4 solid solution was formed on the surface of LiMn2O4 particles. And charge-discharge tests showed that the enhancement of the capacity retention of modified LiMn2O4 is significant, maintained 97.2% of the maximum capacity after 100 cycles at charge and discharge rate of C/2, while the pure one only 75.2%. The modified LiMn2O4 also results in a distinct improvement in rate capability, even at the rate of 12C. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion at the surface of spinel LiMn2O4 particles. 相似文献
15.
The complex electrical impedance of Na3H(SO4)2 along the bm-axis has been measured from 25°C to 316°C in the frequency range 4 kHz–40 MHz. The temperature dependence of the electrical conductivity shows remarkable changes in the temperature range 160°C–260°C. The sample crystal becomes a fast ionic conductor above 260°C. The conduction mechanisms of proton and sodium ions in the different phases are analyzed in detail with respect to the structural features of the sample crystal. 相似文献
16.
J. Zaleski T. Glowiak R. Jakubas L. Sobczyk 《Journal of Physics and Chemistry of Solids》1989,50(12):1265-1269
A new [(C2H5)4N]6Bi8Cl30 crystal of the family of alkylammonium halogenobismuthates was grown. X-ray diffraction studies showed that the crystals are monoclinic, space group C2/m with a = 20.117(5), b = 12.682(3), c = 20.396(5) Å, β = 93.03(3), Z =2. The lattice consists of (C2H5)4N+ cations and a new type of Bi8Cl6−30 anion. Dielectric studies revealed two closely-lying structural phase transitions around 241 K (on cooling). They were interpreted as due to a freezing of the rotational motions of tetraethylammonium cations. 相似文献
17.
The orthorhombic Sm5Ge4-type Tb2Ti3Ge4 shows square modulated non-collinear magnetic ordering with wave vector K=[±1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) μB/Tb is obtained at 2 K. 相似文献
18.
Sergei A. JerebetsMingqin Zou Roger D. Willett 《Journal of Physics and Chemistry of Solids》2002,63(5):793-799
The compound (Me4P)2ZnBr4, a member of the β-K2SO4 structure class, undergoes a phase transition at 84°C from the room temperature space group P121/c1 to the parent Pmcn structure. The room temperature structure corresponds to a ferrodistortive transition of B1g symmetry at the zone center. At room temperature, the compound has lattice constants a=9.501(1), b=16.055(2), c=13.127(2) Å and β=90.43(1)°. For the high temperature phase, the orthorhombic cell has dimensions a=9.466(2), b=16.351(3) and c=13.284(2) Å. The structures consist of two crystallographically independent Me4P+ cations and the ZnBr42− anions. In the room temperature phase, all three ionic species show substantial displacement from the mirror plane perpendicular to the a-axis that exists in the high temperature phase, as well as rotations out of that plane. The thermal parameters of the cations are indicative of substantial librational motion. Measurements of lattice parameters have been made at 2-5°C intervals over the temperature range 40-140°C. The changes in the lattice constants appear continuous at Tc (within experimental limits) indicating that the phase transition is likely second-order. The a lattice constant shows an anomalous shortening as Tc is approached. Thermal expansion coefficients are calculated from this data. An application of Landau theory is used to derive the temperature dependencies of spontaneous shear strain and corresponding elastic stiffness constants associated with the primary order parameter. 相似文献
19.
Uniaxial strain induced ferroelectric phase transitions in rutile TiO2 are investigated by first-principles calculations. The calculated results show that the in-plane tensile strain induces rutile TiO2, paraelectric phase with P4-2/mnm (D4h) space group, to a ferroelectric phase with Pm (Cs) space group,driven by the softening behaviour of the E_u1 mode. In addition, the out-of-plane tensile strain, vertical to the ab plane, leads to a ferroelectric phase with P42nm (C4v) space group, driven by the softening behaviour of the A2u mode. The critical tensile strains are 3.7% in-plane and 4.0% out-of-plane, respectively. In addition, the in-plane compression strain, which has the same structure variation as out-of-plane tensile strain due to Poisson effect, leads the paraelectric rutile TiO2 to a paraelectric phase with Pnnm (D2h) space group driven by the softening behaviour of the B1g mode. These results indicate that the sequence ferroelectric (or paraelectric) phase depends on the strain applied. The origin of ferroelectric stabilization in rutile TiO2 is also discussed briefly in terms of strain induced Born effective charge transfer. 相似文献
20.
Magnetic phase transition and the corresponding magnetostriction of intermetallic compounds RMnsGe2(R=Sm,Gd)
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The temperature dependence of lattice constants a and c of intermetallic compounds RMn2Ge2 (R=Sm, Gd) is measured in the temperature range 10-800K by using the x-ray diffraction method. The magnetoelastic anomalies of lattice constants are found at the different kinds of spontaneous magnetic transitions. The transversal and longitudinal magnetostrictions of polycrystalline samples are measured in the pulse magnetic field up to 25T. In the external magnetic field there occurs a first-order field-induced antiferromagnetism-ferromagnetism transition in the Mn sublattice, which gives rise to a large magnetostriction. The magnitude of magnetostrictions is as large as 10-3. The transversal and longitudinal magnetostrictions have the same sign and are almost equal. This indicates that the magnetostriction is isotropic and mainly caused by the interlayer Mn-Mn exchange interaction. The experimental results are explained in the framework of a two-sublattice ferrimagnet with the negative exchange interaction in one of the sublattices by taking into account the lattice constant dependence of interlayer Mn-Mn exchange interaction. 相似文献