Magnetic structure and thermodynamic properties of TmPtIn

Physical properties of TmPtIn have been investigated by means of magnetic, electrical transport, calorimetric as well as neutron diffraction measurements. The compound crystallizes in the hexagonal ZrNiAl-type crystal structure. It orders antiferromagnetically below T_N = 3.5 K with the Tm magnetic moments confined to the basal hexagonal plane. They form a non-collinear “triangular” magnetic structure that may be described by the propagation vector . At 1.6 K, the Tm magnetic moment is equal to 5.59(9)μ_B. The antiferromagnetic character of the electronic ground state is reflected in the low temperature behaviors of the magnetic susceptibility and the specific heat, which may be described by spin-wave theory of antiferromagnetic magnons with linear dispersion relation. The compound exhibits metallic character of electrical conduction.     

Crystal structure and magnetic properties of TbFe0.4Ge2 compound

Neutron diffraction and magnetic measurements were performed on polycrystalline TbFe_0.4Ge₂ 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.     

Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4

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) μ_B/Tb is obtained at 2 K.     

The magnetic structure of the compound Ho5Sb3

We have investigated the magnetic behavior of Ho₅Sb₃ compound (Mn₅Si₃-type, hexagonal; a=0.8865(1) nm, c=0.6232(1) nm, as derived from X-ray Guinier powder pattern) by using the techniques of magnetization, electrical resistivity, heat capacity and neutron diffraction. We find that Ho₅Sb₃ exhibits a ferrimagnetic type (Ferrimagnet I) ordering below 60 K with propagation vectors K₀=[0, 0, 1] and K₁=[±K_x, 0, 0]. Below 40 K, the thermal variation of magnetic reflections and the appearance of an additional magnetic component with propagation vector K₂=[0, 1/2, 0] show the onset of an antiferromagnetic type of ordering in the magnetic structure; which evolves into yet another ferrimagnetic structure (Ferrimagnet II) as the temperature is lowered down to 2 K. The magnetic moments of the Ho atoms at the (4d) and (6g) sites with magnitudes of nearly 7.4 and 6.3 μ_B at 2 K, respectively, are inclined approximately at 70° to the c-axis.     

Magnetic structure of the La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3−x (x=0 and 0.3)

We present a neutron powder diffraction investigation of the magnetic structure of La₃NiGe₂-type Tb₃NiGe₂ and Mn₅Si₃-type Tb₅Ni_xGe_3−x (x=0, 0.3) compounds. It is found that below∼135 K Tb₃NiGe₂ exhibits a commensurate b-collinear ferrimagnetic ordering with C_2h′={1, m_z, 1′×2_z, 1′×1?} magnetic point group. The Mn₅Si₃-type Tb₅Ge₃ and Tb₅Ni_0.3Ge_2.7 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 Tb₅Ni_0.3Ge_2.7 (below ∼10 K).     

Magnetic structures of R3Cu4Si4 (R=Dy, Ho and Er)

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.     

Low temperature magnetic structure of MnSe

In this paper we report low temperature neutron diffraction studies on MnSe in order to understand the anomalous behaviour of their magnetic and transport properties. Our study indicates that at low temperatures MnSe has two coexisting crystal structures, high temperature NaCl and hexagonal NiAs. NiAs phase appears below 266 K and is antiferromagnetically ordered at all temperatures while the NaCl phase orders antiferromagnetically at 130 K.     

Magnetic order of Mn5Si3-type Tb5Sb3 and Tb5Si1.5Sb1.5

Neutron diffraction study has been performed on the Tb₅Sb₃ and Tb₅Si_1.5Sb_1.5 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 Tb₅Si_1.5Sb_1.5 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 Tb₅Si_1.5Sb_1.5 have the different magnetic structure in the full temperature range.     

Magnetic structure of the Mn5Si3-type Er5Ge3 compound

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, M_z≈M₀ cos [2π(Z–1/4)(1–kZ)], with M₀=9.2(2) μ_B at 4 K.     

Internal structure of magnetic endosomes

The internal structure of biological vesicles filled with magnetic nanoparticles is investigated using the following complementary analyses: electronic transmission microscopy, dynamic probing by magneto-optical birefringence and structural probing by Small Angle Neutron Scattering (SANS). These magnetic vesicles are magnetic endosomes obtained via a non-specific interaction between cells and anionic magnetic iron oxide nanoparticles. Thanks to a magnetic purification process, they are probed at two different stages of their formation within HeLa cells: (i) adsorption of nanoparticles onto the cellular membrane and (ii) their subsequent internalisation within endosomes. Differences in the microenvironment of the magnetic nanoparticles at those two different stages are highlighted here. The dynamics of magnetic nanoparticles adsorbed onto cellular membranes and confined within endosomes is respectively 3 and 5 orders of magnitude slower than for isolated magnetic nanoparticles in aqueous media. Interestingly, SANS experiments show that magnetic endosomes have an internal structure close to decorated vesicles, with magnetic nanoparticles locally decorating the endosome membrane, inside their inner-sphere. These results, important for future biomedical applications, suggest that multiple fusions of decorated vesicles are the biological processes underlying the endocytosis of that kind of nanometric materials.     

Magnetic properties of the intermetallic compound Ce5Ge4

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 (T_C). 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 0.8μ_B/Ce³⁺ is obtained compared to the free ion value of 2.14μ_B/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 T_C, 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.     

The temperature evolution of the magnetic correlations in pure and diluted spin ice Ho2−xYxTi2O7

Diffuse polarized neutron scattering studies have been carried out on single crystals of pyrochlore spin ice Ho_2−xY_xTi₂O₇ (x=0, 0.3, and 1) to investigate the effects of doping and anisotropy on spin correlations in the system. The crystals were aligned with the (1 −1 0) orientation coincident with the direction of neutron polarization. For all the samples studied the spin flip (SF) diffuse scattering (i.e. the in-plane component) reveals that the spin correlations can be described using a nearest-neighbour spin ice model (NNSM) at higher temperatures (T=3.6 K) and a dipolar spin ice model (DSM) as the temperature is reduced (T=30 mK). In the non-spin flip (NSF) channel (i.e. the out-of-plane component), the signature of strong antiferromagnetic correlations is observed for all the samples at the same temperature as the dipolar spin ice behaviour appears in the SF channel. Our studies show that the non-magnetic dopant Y does not significantly alter SF or NSF scattering for the spin ice state, even when Y doping is as high as 50%. In this paper, we focus on the experimental results of the highly doped spin ice HoYTi₂O₇ and compare our results with pure spin ice Ho₂Ti₂O₇. The crossover from a dipolar to a nearest-neighbour spin ice behaviour and the doping insensitivity in spin ices are briefly discussed.     

High-pressure synthesis,structure and magnetic properties of LaCrO3 ceramics

Single-phase LaCrO₃ ceramics was synthesized successfully by the solid state sintering method under high pressure (5 GPa). X-ray diffraction measurements suggest that the high-pressure synthesized sample is well-crystallized, but the cell volume is larger than that of the sample synthesized under ambient pressure, which can be ascribed to the occurrence of Cr²⁺ converted form part of Cr³⁺. Such mixed valent state with coexistence of Cr²⁺ and Cr³⁺ could be confirmed by X-ray photoelectron spectroscopy measurements. Magnetic measurement results indicate that in addition to antiferromagnetic superexchange interaction of Cr³⁺-O-Cr³⁺ network accompanied by weak ferromagnetism at high temperature, another kind of ferromagnetic behavior can be observed at low temperature (below 30 K), which could be attributed to double exchange interaction of Cr²⁺-O-Cr³⁺ networks.     

Magnetic behaviour of TbMnFe

Neutron diffraction and M?ssbauer measurements have been carried out on the cubic Laves phase intermetallic TbMnFe. The magnetic moment on the transition metal atom is found to be low, 0.2μ _B, at room temperature. This moment is temperature independent down to 10 K. Magnetic moment on the rare earth atom varies from 2.5μ _B at 296 K to 7.27μ _B at 10 K. M?ssbauer spectra recorded at 298 K and 78 K have magnetic character but there is a large distribution of hyperfine field values. Both these features arise due to magnetic frustration created in the sample due to the competing ferro and antiferromagnetic interactions between the transition metal atoms.     

稀土配合物的喇曼散射和超喇曼散射效应

以可见光为激发光,观测了稀土配合物的喇曼散射和超瑞利、超喇曼散射光谱,简单论述了超瑞利和超喇曼散射的理论,对实验测出的谱线进行了认证与分析     

Local structure of polymeric ferrogels

We synthesize hybrid gels incorporating γ‐Fe₂O₃ nanoparticles (NPs), citrate coated, in a polyacrylamide (PAM) network. The local organisation and the rotational degrees of magnetic nanoparticles are probed in the conditions of gel synthesis and also at swelling equilibrium, to correlate the homogeneous/inhomogeneous structure of the ferrogels to the synthesis parameters and to their macroscopic elasticity. NP adsorption on the PAM network at low citrate concentration is responsible for the reinforcing of the polymer structure. At higher citrate concentration, due to a competition between citrate and NPs, the nanoparticles desorb from the polymer structure weakening the system.     

Spin-Wave Analysis of the Spin-1 Two-Dimensional Frustrated Heisenberg Antiferromagnet with the Single-Ion Anisotropy

In this paper,the low-temperature properties of the spin-1 two-dimensional frustrated Heisenberg antiferromagnet with the single-ion anisotropy are investigated on a square lattice by using the spin-wave theory.The influence of the frustration and anisotropy is found in the thermodynamics of the model,such as the temperature dependence of the staggered magnetization and specific heat.For some selected values of the frustration and anisotropy parameters,the results for the specific heat are compared with those of existing theories and numerical estimates.Within a spin-wave analysis,we have found the evidence for an intermediate magnetically disorder phase to separate the N′eel and collinear phases.     

Magnetostructural phase transitions of DyFe4Ge2: Part II Neutron diffraction

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 T_ic1=28K:

The re-entrant lock-in magnetic phase is stable in the high-temperature range T_ic2–T_N and in the low-temperature range 1.5 K–T_ic1 while the incommensurately modulated magnetic phase is sandwiched in the intermediate range T_ic1–T_ic2 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 T_ic2 transition is connected with reorientations of both Fe and Dy moments.