铁电磁体Pb(Fe1/2Nb1/2)O3相变特征

借助与示差扫描量热法、磁化率测量、电子自旋共振、铁电与介电性质测量及电子衍射系统地研究了Pb(Fe_1/2Nb_1/2)O₃(PFN)的电、磁性质和相变特征．结果表明发生在380K附近的顺电－铁电转变和发生在145K附近的顺磁 反铁磁转变分别为一级相变和二级相变或弱一级相变．在室温下,PFN的剩余极化与矫顽场分别为11.5μC/cm²和3.04kV/cm.介电测量表明PFN的顺电-铁电相变为弥散型相变．其弥散指数为1.62.电子衍射表明Fe³⁺与Nb⁵⁺离子在B位置上是无序分布的,正是这种与无序分布相关联的成分涨落导致铁电相变的弥散性. 关键词：     

A study of the conduction mechanism of single crystal Li0.5Fe2.5O4 through the transition points

The differential thermal analysis, electrical resistivity and thermopower are studied as a function of temperature in the range 300–1100 K. The measurements show two transition points at 905 and 1030 K. The first point is linked with the magnetic transition at the Néel temperature (T_N), and the second with the order-disorder phase. The conduction mechanism through the Néel point is discussed using the spin polaron model.     

The temperature dependence of the angular variation of,and the critical point exponent for the EPR linewidth in the two-dimensional canted antiferromagnetic (C2H5NH3)2MnBr4: Evidence for a structural phase transition

The angular variation of the EPR linewidths in single crystals of (C₂H₅NH₃)₂MnBr₄ has been measured as a function of temperature. The angular dependence is well characterized by δH(θ) = a + b(3 cos²θ ? 1) + c(3 cos²θ ? 1)². The temperature dependence of the expansion coefficients is reported, and the effect of critical point fluctuations near the Néel temperature as well as a linear temperature dependence at high temperature are observed. A sharp decrease in linewidths at 160°K is attributed to a structural phase transition. The Néel temperature is determined to be 46°K (± 1°) from linewidth measurements of a powder sample. The linewidths diverge exponentially near the Néel temperature with a critical point exponent of 1.5.     

A neutron diffraction study of the coexistence of antiferromagnetism and superconductivity in GdMo6S8

The present neutron diffraction study confirms that GdMo₆S₈ orders antiferromagnetically in the superconducting state at a Néel temperature T_N = 0.84 K. Previous neutron scattering studies have demonstrated the coexistence of antiferromagnetism and superconductivity in two other rare earth ternary compounds, DyMo₆S₈ and TbMo₆S₆.     

Investigation of La1−x Ca x FeO3−y (0≦x≦0.50) by means of X—ray diffraction and Mössbauer spectroscopy

Compounds La_1?x Ca _x FeO_3?y (0≤x≤0.50) were prepared and characterized by X-ray diffraction and Mössbauer measurements. The diffraction patterns were defined to be orthorhombic. The lattice constants of orthorhombic perovskite La_1?x Ca _x FeO_3?y decrease linearly with increasingx. The Mössbauer spectra at room temperature indicate that the Néel temperature drops and the isomer shift decreases with increasingx. The spectrum of La_0.50 Ca_0.50 FeO_3?y at 80 K shows two hyperfine splitting patterns which may be related to the Fe³⁺ and Fe⁵⁺ ions.     

Neutron diffraction study of the (1-x)αFe2O3xAl2O3 system

The magnetic structure of the (1-x) α Fe₂O₃xAl₂O₃ system with x= 0–0.1 has been investigated on polycrystalline samples by neutron diffraction method. The Morin transition temperature and the Néel temperature are observed to decrease on increasing x. The angle by which the magnetic moments turn out of the basal plane in the Morin transition also decreases with increasing x. The Morin transition does not occur above x = 0.09.     

Neutron diffraction study of Ho(Rh0.3Ir0.7)4B4

Using powder neutron diffraction techniques, we have examined the magnetic order of the pseudoternary compound Ho(Rh_0.3Ir_0.7)₄B₄ below the Néel temperature T_N=2.7K. The magnetic structure consists of stacked antiferromagnetic basal plane sheets forming a body centered tetragonal unit cell, with a sublattice magnetization corresponding to 9.6±0.6μ_B per Ho³⁺ion at 1.5 K. Magnetic intensity versus temperature measurements indicate that the transition is second order and reveal no anomalous effects when the compound becomes superconducting at T_c=1.34K.     

Theoretical study of magnetic susceptibility of orbitally unquenched compound KCoF3

The effect of residual orbital magnetic moment of Co²⁺ in KCoF₃ on the magnetic susceptibility has been studied. For the calculation for both the ordered state and the paramagnetic state we have applied the correlated effective field approximation developed by Lines. An excellent value of the Néel temperature is obtained and, except near the Néel temperature, the calculated susceptibility agrees well with the experimental results over the whole temperature range.     

Neutron diffraction study of RECo2Si2 intermetallics

A neutron diffraction study of polycrystalline RECo₂Si₂ intermetallics (RE = Pr, Nd, Tb, Ho, Er) carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic ordering of +?+? type. Magnetic moment is localized on RE ions only and amounts to the RE³⁺ free ion value. In ErCo₂Si₂ the magnetic moment is normal to the tetragonal unique axis, whereas in the remaining compounds the magnetic moment is aligned along it. Néel points were determined from the temperature dependence of magnetic peak heights.     

Nouvelles donnes experimentales sur les proprietes magnetiques de Cr3 Se4 et des solutions solides Cr3 Set S4−t

Magnetic susceptibility and specific heat measurements and neutron diffraction experiments allow to locate Néel temperatures T_N and also two types of transitions below T_N. At T_t of order T_N/2 the susceptibility is maximum, and the magnetic structure is modified (for Se-rich compounds). The second transition takes place around 15 K and is characterized by a specific heat peak and a susceptibility anomaly but no modification of the magnetic structure, according to our powder diffraction data.     

Magnetic properties of NdCo2Ge2, ErCo2Ge2 and PrFe2Ge2 compounds

Magnetometric and neutron diffraction studies of polycrystalline NdCo₂GE₂, ErCo₂Ge₂ and PrFe₂Ge₂ compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ～ 4.2 and 13 K, respectively. The RECo₂Ge₂ compounds have collinear antiferromagnetic order of +?+? type. For PrFe₂Ge₂ a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE³⁺ free ion value. In ErCo₂Ge₂ the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis.     

Antiferromagnetic metallic state of NiS2

The neutron diffraction experiment we have made on NiS_1.91 single crystal under increasing pressure (0<P<30 kbar) indicates a constant increase of the Néel temperature of the sample. For high pressures (P>20 kbar) and low temperatures the sample is in an antiferromagnetic metallic state as suggested by theoretical considerations for a Mott-Hubbard insulator. The pressure dependence of the second magnetic transition in NiS₂ (T = 31 K for P = 0) is also reported.     

Susceptibility measurements on some R5In3 compounds

The magnetic susceptibility of some rare earth-indium compounds has been measured in the temperature range 4.2–300 K under a constant field of 1 kOe. The compounds with R = Gd, Tb and Dy are antiferromagnetic, having Néel temperatures between 4.2 and 78 K ; those with R = Ho, Er and Tm seem to be ferromagnetic with ordering temperatures probably below 4.2 K. Y₅In₃ presents a temperature independent susceptibility.     

Phase diagrams of CuCl2·2NC5H5 and CsCuCl3

The phase diagrams of two quasi one-dimensional,$\text{S =}\text{1}\text{2}$ quantum systems CuCl₂·2NC₅H₅ and CsCuCl₃, have been determined experimentally for fields between 0 and 90 kOe. The results show an increase of the Néel temperature as a function of the field, in accordance with earlier observations on manganese systems.     

Low temperature properties of the metallic antiferromagnet ErZn12

The metallic antiferromagnet ErZn₁₂ orders magnetically at 2·76°K. We report measurements of the susceptibility, magnetisation, resistivity and specific heat of polycrystalline specimens of it in the vicinity of the magnetically ordered regime. We find evidence for a metamagnetic or spin-flop transition in fields of 3–7KOe. The resistivity increases monotonically from low temperature to the Néel point and has a power-law dependence on temperature of Tⁿ, where n～6·5. The specific heat shows a lambda anomaly at the Néel point and the divergences which appear above and below it are compared with those reported previously in the resistivity. The magnetic entropy indicates that the ordering process involves only one crystal-field doublet.     

Directional frustration of magnetic moments in (U0.50Dy0.50)Ni2B2C

Polycrystalline (U_0.50Dy_0.50)Ni₂B₂C solid solution was prepared and found by X-ray diffraction to crystallize in BCT LuNi₂B₂C-type structure (space group I4/mmm) of the end compounds UNi₂B₂C and DyNi₂B₂C. AC susceptibility and magnetization show paramagnetic behavior down to 6.5 K, with the values θ=−5(5) K and μ_eff=7.7(1) μ_B, compatible with those of the end compounds, and indicate possible cooperative phenomena at lower temperatures. The observed paramagnetism, at variance with antiferromagnetic ordering in (Pr_0.50Dy_0.50)Ni₂B₂C, is attributed to a directional frustration of the magnetic moments on the (U,Dy) site.     

Magnetic order in an MnF2 epitaxial layer with the orthorhombic structure

The magnetic structure of MnF₂ is determined by the neutron diffraction method in the metastable orthorhombic phase grown in the form of thin (～1 μm) film on a CaF₂ buffer layer by the molecular beam epitaxy method. The magnetic moments of Mn⁺⁺ form a simple two-sublattice antiferromagnetic structure and are directed along the c crystallographic axis parallel to the film plane. Using the temperature dependence of magnetic reflections, a Néel temperature of 67.19(7) K and a critical index of 0.50(2), which corresponds to the mean field approximation, are determined.     

Neutron diffraction study of antiferromagnetism in YbVO4

The antiferromagnetism of YbVO₄ has been studied by neutron diffraction down to 50 mK. The structure is collinear with the spins along the c-axis. The Néel point is at 93 mK and the saturated moment on the ytterbium is (3.1 ± 0.16)μB. The results are in reasonable agreement with Mössbauer work.     

The antiferromagnetic structure of TbB4

The magnetic structure of the rare earth tetraboride TbB₄ (crystallographic space group P4/mbm) has been determined by neutron diffraction on a polycrystalline sample. Below the experimentally determined Néel temperature of T_N = (43±1) K TbB₄ is ordered antiferromagnetically. The data refinement yielded a magnetic moment value of (7.7 ± 0.2) μ_B/Tb ion at 4.2 K which we interpret as Tb⁴⁺. The magnetic structure is antiferromagnetic collinear with the moments perpendicular to the tetragonal axis.     

Domain wall energy in ErCrO3

Domain structure in ErCrO₃ was studied from 10 K up to the Néel temperature by means of Faraday effect. Experimental temperature dependence of domain wall energy was obtained. Using a two-sublattice molecular-field model, the expression for the domain wall energy density was derived. It was shown that domain walls in ErCrO₃ have a Bloch wall character with the rotation of the sublattice magnetization in (ac) plane.