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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.
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
3.
A.V. Morozkin Jinlei Yao Y. Mozharivskyj O. Isnard 《Journal of magnetism and magnetic materials》2012
We present a neutron powder diffraction investigation of the magnetic structure of La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3−x (x=0, 0.3) compounds. It is found that below∼135 K Tb3NiGe2 exhibits a commensurate b-collinear ferrimagnetic ordering with C2h′={1, mz, 1′×2z, 1′×1?} magnetic point group. The Mn5Si3-type Tb5Ge3 and Tb5Ni0.3Ge2.7 compounds are found to present a flat spiral type antiferromagnetic ordering at 85 and ≥89 K, respectively. The Ni for Ge substitution is found to decrease the flat spiral ordered magnetic unit cell from a×a×40c of Tb5Ge3 (below 40 K) down to a×a×5c for Tb5Ni0.3Ge2.7 (below ∼10 K). 相似文献
4.
Neutron diffraction study has been performed on the Tb5Sb3 and Tb5Si1.5Sb1.5 compounds (hexagonal Mn5Si3-type, hP16, P63/mcm) to understand their magnetic structures. The temperature dependence of neutron diffraction results proves that these intermetallics show a complex magnetic ordering. The Tb5Sb3 presents five subsequent changes in magnetic structure at ∼150, 119, 85, 70 and 54 K on cooling: paramagnet→antiferromagnetic flat spiral→ferromagnetic cone→antiferromagnetically canted ferromagnetic cone→canted AF→sine modulated AF. The Tb5Si1.5Sb1.5 shows two subsequent changes in magnetic structure at 123 and 66 K: paramagnet→sine modulated antiferromagnet I→sine modulated antiferromagnet II. The Tb5Si3, Tb5Sb3 and Tb5Si1.5Sb1.5 have the different magnetic structure in the full temperature range. 相似文献
5.
The Er5Ge3 compound (Mn5Si3-type, hP16, P63/mcm) at 4 K shows magnetic ordering of the antiferromagnetic type. Its magnetic structure consists of sine modulated collinear magnetic moments of Er that are parallel to the c axis (with a propagation vector k=[0 0 ±0.3]). This corresponds to the magnetic unit cell (a a 10c), the values of the magnetic moment of the Er atoms being, as a general formula, Mz≈M0 cos [2π(Z–1/4)(1–kZ)], with M0=9.2(2) μB at 4 K. 相似文献
6.
Y.W. Long L.X. Yang Y.X. Lv Ying Chen C.Q. Jin 《Journal of magnetism and magnetic materials》2010,322(14):1912-1916
The crystal and magnetic structures of DyCrO4 were studied using neutron powder diffraction. Complete diffraction data at 3.6, 17, 27, and 40 K show that a crystal structural phase transition from tetragonal I41/amd to orthorhombic Imma symmetry is found to take place between 27 and 40 K. This transition does not involve a significant change in the unit cell volume. Strong ferromagnetic reflections are observed at 3.6 and 17 K, and can be fit well using the magnetic model of space group Im'ma', with the moments of both Dy3+ and Cr5+ ions aligning along the y-axis. Detailed temperature dependent magnetic intensities of 101/011 and 211/121 peaks reveal a Curie temperature of Tc=22.35(15) K. 相似文献
7.
Neutron diffraction and magnetic measurements were performed on polycrystalline TbFe0.4Ge2 which crystallizes with the orthorhombic structure of the CeNiSi2-type. Despite the presence of some clear anomalies in the low-temperature magnetic susceptibility, the neutron diffraction experiment did not reveal any long-range magnetic ordering of the Tb magnetic moments down to 1.57 K. 相似文献
8.
《Journal of magnetism and magnetic materials》2004,280(2-3):234-242
Polycrystalline samples of R3Cu4Si4 (R=Dy, Ho, Er) intermetallics were studied with neutron diffraction methods. All of them crystallize in the orthorhombic structure of Gd3Cu4Ge4-type and order antiferromagnetically at low temperatures. Magnetic moments localized at the rare earth atoms, that occupy two non-equivalent 2d and 4e sublattices, order simultaneously in Dy3Cu4Si4. The order is described by the propagation vector
accompanied by
, δ=0.025(2). In Ho3Cu4Si4 two propagation vectors are needed to model the magnetic order. These are:
for the 4e sublattice, which disorders as the first when the temperature increases, and
for the 2d sublattice. A similar situation is observed for Er3Cu4Si4 where the propagation vectors are: k=(0,1−δ,0), δ=0.097(2) for the 4e sublattice, which disorders as the first with increasing temperature, and
, δ=0.0015(6) for the 2d sublattice. 相似文献
9.
10.
11.
B. Penc S. GerischerA. Hoser A. Szytu?a 《Journal of magnetism and magnetic materials》2012,324(5):657-659
TmCu2Ge2 compound crystallizes in the tetragonal ThCr2Si2-type crystal structure. The neutron diffraction reveals the presence of an incommensurate antiferromagnetic order below TN=2.5 K. The Tm magnetic moment of 5.0(1) μB at 0.47 K is parallel to the c-axis. The order is described by the propagation vector k=[kx, kx, 0], where kx=0.117(3). The increase of the values of the components kx near the Néel temperature is observed. 相似文献
12.
13.
C.A. Bridges V.V. Krishnamurthy S. Poulton M.P. Paranthaman B.C. Sales C. Myers S. Bobev 《Journal of magnetism and magnetic materials》2009,321(22):3653-3657
This paper reports a neutron powder diffraction study of CaMn2Sb2 in the temperature range of 20–300 K. Collinear long-range antiferromagnetic order of manganese ions occurs below 85 K, where a transition is observed in the dc magnetic susceptibility measured with a single crystal. Short-range magnetic order, characterized by a broad diffraction peak corresponding to a d-spacing of approximately 4 Å (2θ≈22°), is also observed above 20 K. The long-range antiferromagnetic order is indexed by the chemical unit cell, indicating a propagation vector k=(0 0 0), with a refined magnetic moment of 3.38 μB at 20 K. Two possible magnetic models have been identified, which differ in spin orientation for the two manganese ions with respect to the ab plane. The model with spins oriented at a 25±2° angle relative to the ab plane gives an improved fit compared to the other model in which the spins are constrained to the ab plane. Representational analysis can account for a model involving a c-axis component only by the mixing of two irreducible representations. 相似文献
14.
R. Nirmala A.V. Morozkin A.K. Nigam 《Journal of magnetism and magnetic materials》2009,321(3):188-191
Magnetization and neutron diffraction studies have been performed on Ce4Sb3 compound (cubic Th3P4-type, space group I4¯3d, no. 220). Magnetization of Ce4Sb3 reveals a ferromagnetic transition at ∼5 K, the temperature below which the zero-field-cooled and field-cooled magnetization bifurcate in low applied fields. However, a saturation magnetization (MS) value of only ∼0.93μB/Ce3+ is observed at 1.8 K, suggesting possible presence of crystal field effects and a paramagnetic/antiferromagnetic Ce3+ moment. Magnetocaloric effect in this compound has been computed using the magnetization vs. field data obtained in the vicinity of the magnetic transition, and a maximum magnetic entropy change, −ΔSM, of ∼8.9 J/kg/K is obtained at 5 K for a field change of 5 T. Inverse magnetocaloric effect occurs at ∼2 K in 5 T indicating the presence of antiferromagnetic component. This has been further confirmed by the neutron diffraction study that evidences commensurate antiferromagnetic ordering at 2 K in zero magnetic field. A magnetic moment of ∼1.24μB/Ce3+ is obtained at 2 K and the magnetic moments are directed along Z-axis. 相似文献
15.
A. M. Balagurov E. V. Raspopina V. V. Sikolenko I. S. Lyubutin A. S. Stepin A. V. Gribanov G. Andr F. Boure H. M. Duh 《Journal of magnetism and magnetic materials》2000,210(1-3)
The neutron diffraction and magnetic susceptibility studies have shown that the magnetic structure of UPd2Ge2 changes dramatically even under very low iron doping. Though the general magnetic structure of pure UPd2Ge2 and of 1%Fe-doped samples is the same, the temperature intervals of existence of different magnetic phases are different. The values of transition temperatures, where (i) the ‘square’ modulated longitudinal spin-density wave (LSDW) structure with the propagation vector k=(0; 0;
) starts to transform into the sinusoidal modulated LSDW structure and (ii) the commensurate phase transforms into incommensurate one, shift under the 1%Fe doping to the higher temperatures (from 50 to 65 K and from 80 to 90 K, respectively). In the pure and 1%Fe-doped UPd2Ge2, the magnetic transition from the commensurate to incommensurate phase is accompanied by the drastic decrease of the propagation vector kz. In the 2%Fe-doped sample, besides the Néel point of TN=135 K, we have found two additional characteristic temperatures of 65 and 93 K. Below 65 K, the material has a simple antiferromagnetic (AF) structure with the propagation vector k=(0; 0; 1) and, at 65 K<T<TN, the magnetic structure is LSDW with sinusoidal modulation. Over almost the total region 65 K<T<TN, the LSDW magnetic structure is incommensurate. Only at about 93 K, the propagation vector passes the commensurate value of
, whereas
at 65<T<93 K and
at 93 K<T<TN. We have found that the magnetic susceptibility and the uranium magnetic moment are sensitive to the
transition. With increasing iron concentration to x0.15, the simple AF structure with k=(0; 0; 1) develops over all temperature region up to the Néel point. Below TN, the uranium magnetic moments are always parallel to the tetragonal c-axis. 相似文献
16.
The magnetic properties of the PrPd2Ge2 and NdPd2Ge2 compounds have been investigated by magnetic measurements, specific heat measurements and neutron diffraction experiments. The PrPd2Ge2 compound orders antiferromagnetically below TN=5.0(2) with an original modulated magnetic structure characterized by a magnetic cell three times larger than the chemical one by tripling of the c parameter. The palladium atom is non magnetic and the Pr moments are parallel to the c-axis with a value of ≈2.0 μB at 2 K. The specific heat measurements clearly detect a low temperature transition for the NdPd2Ge2 compound, interpreted as a Nd sublattice antiferromagnetic ordering below 1.3(2) K. 相似文献
17.
F. Genet S. Loridant C. Ritter G. Lucazeau 《Journal of Physics and Chemistry of Solids》1999,60(12):6521-2021
Polycrystalline samples and small single crystals of the perovskite BaCeO3 were studied by neutron diffraction and Raman spectrometry between 300 and 1200 K. The controversy about the phase transitions originally deduced from our previous Raman study and those observed since by neutron diffraction by Knight has stimulated this work. Pretransitional effects which are detected by Raman much before long-range ordering takes place can partly explain the above disagreement. A continuous monitoring of the structural changes by neutron diffraction and by Raman spectroscopy including polarization analysis has allowed discussion of the transition mechanisms: The first transition Pnma–Imma takes place at 573 K and is of second order. Although some modes soften when the temperature is raised as in many of these perovskite compounds the transition is likely partly displacive partly order–disorder. The Raman modes which disappear transform in modes at the X point of the Brillouin zone of the Imma phase. The second transition Imma–R
c takes place at 673 K and is first order. The last transition R
c–Pm3m occurs above 1200 K and the transition temperature which can be deduced by extrapolation to zero Raman intensity is in good agreement with neutron results. This second order transition is progressive and begins at about 400 K, the intermediate R
c structure appearing as an attempt for slowing down the structural evolution toward the cubic perovskite form. 相似文献
18.
Magnetic and magnetocaloric properties of the compound Ce5Ge4 have been studied. This compound has orthorhombic Sm5Ge4-type structure (space group Pnma, no. 62) and orders ferromagnetically at ~12 K (TC). The paramagnetic Curie temperature is ~−20 K suggesting the presence of competing ferromagnetic and antiferromagnetic interactions in this compound. The magnetization does not seem to saturate even in fields of 90 kOe at 3 K consistent with the presence of competing interactions. Saturation magnetization value (extrapolated to 1/H→0) of only 0.8μB/Ce3+ is obtained compared to the free ion value of 2.14μB/Ce3+. This moment reduction in the ordered state of Ce5Ge4 could be due to partial antiferromagnetic/paramagnetic ordering of the Ce moments and may also be due to crystalline electric field effects. Magnetic entropy change near TC, calculated from the magnetization vs. field data, is found to be moderate with a maximum value of ~9 J/kg/K at ~11 K for a field change of 90 kOe. 相似文献
19.
T. Chatterji J. CombetB. Frick A. Szyula 《Journal of magnetism and magnetic materials》2012,324(6):1030-1033
We have investigated the low energy nuclear spin excitations in NdMn2Si2 and NdMn2Ge2 by high resolution inelastic neutron scattering. Previous neutron diffraction investigations gave ambiguous results about Nd magnetic ordering at low temperatures. The present element-specific technique gave direct evidence for the magnetic ordering of Nd ions. We found considerable difference in the process of the Nd magnetic ordering at low temperature in NdMn2Si2 and NdMn2Ge2. Our results are consistent with those of magnetization and recent neutron diffraction measurements. 相似文献
20.
M.R. Alinejad N. Tajabor H. Khandan Fadafan D. Fruchart D. Gignoux 《Journal of magnetism and magnetic materials》2007
The magnetoelastic properties of iron-rich REFe10V2 (RE=Nd, Y) compounds were studied via magnetostriction and thermal expansion measurements in the 5–300 K range of temperature in up to 6 T external fields. Results of thermal expansion analysis show that the spontaneous magnetostriction of the compounds mostly originates from itinerant magnetization. Besides, the small volume striction appearing in the thermal expansion of the Nd compound close to 50 K suggests the existence of a basal to conical spin re-orientation transition. The volume magnetostriction isotherms of both compounds take minimum values for external field corresponding to the anisotropy field. In addition, the anisotropic and the volume magnetostriction traces of the NdFe10V2 take marked maxima under low field, with a relatively large initial magnetostrictivity, again more pronounced at the conical–axial spin re-orientation transition (TSR=130 K). Analysis of the anisotropic magnetostriction of the Nd compound leads to the conclusion that the contribution of Nd–Fe interactions is negligible. The temperature dependence of volume magnetostriction is in good agreement with prediction of a phenomenological model based upon a fluctuating local band theory. This analysis shows that the difference between the forced volume strictions of Y and Nd compounds below and above TSR originates from the Nd sublattice magnetization. 相似文献