Spin-reorientation transition and electronic structure of TmCo3 compound

The TmCo₃ compound crystallizes in the rhombohedral PuNi₃-type structure. TmCo₃ exhibits a kink in the resistivity and AC susceptibility near the spin-reorientation temperature (T_SR≅17 K). The spin-reorientation transition observed in TmCo₃ is ascribed to the competition between the anisotropies of Co and Tm atoms. The value of spontaneous magnetization is equal to 3.1 μ_B/f.u. and is closer to the value 3.31 μ_B/f.u. obtained by ab initio calculations, which show that the moments on Co atoms depend on their local environments.     

Spin-reorientation in GdGa

We have determined the magnetic structure of the intermetallic compound GdGa by ¹⁵⁵Gd Mössbauer spectroscopy and neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure. It orders ferromagnetically at T _c ?=?190(2) K and then undergoes a spin reorientation at T _SR ?=?68(2) K. Between T _c and T _SR , the magnetic structure is characterized by ferromagnetic order of the Gd moments along the b-axis. On cooling below T _SR , the Gd 4c magnetic moments split into two groups (2:2). At 3.6 K, the Gd moment is 6.7(4) μ _B , and the Gd magnetic moments are in the bc-plane, canted by 84(3)° and 46(4)° with respect to the crystallographic b-axis. This splitting into two magnetically inequivalent sites is confirmed by our 5 K ¹⁵⁵Gd Mössbauer results.     

Spin-reorientation phase transition: Magnetic resonance, acoustic and optic properties

The problem dealt within this paper is the study of soft modes near the spin-reorientation phase transition (SRPT) in ferromagnets (and partly in antiferromagnets) when the magnetoelastic interaction is taken into account. A detailed discussion is given for the long wavelength magnetoacoustic modes (MAM) and their influence on various physical properties. The results are: the conditions for linear and nonlinear (parametric) excitations of MAM by an ac magnetic field; MAM contributions to the local magnetic susceptibility, nuclear magnetic and magnetoacoustic resonances; the modulation of the sound velocity by an ac magnetic field; and the magnetic birefrigence of light by sound waves. All these phenomena manifest a sharp increase near the SRPT.     

Spin-reorientation phase transition in the basal plane in α-Fe2O3:Ga,Dy

In hematite crystals doped with gallium and dysprosium ions a spin-reorientation phase transition induced in the basal plane by the introduction of dysprosium ions was observed in the temperature range T=15–20 K. The effect is associated with the competition between the anisotropy fields arising from the iron and rare-earth subsystems. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 694–697 (10 May 1996)     

Hyperfine field of156Gd in TbFe2, TbFe3, TbCo2 and TbCo3 compounds

Time integral γ-γ angular correlation measurements have been made on¹⁵⁶Gd in Tb-3d metal compounds, TbFe₂, TbFe₃, TbCo₂ and TbCo₃, using two Ge(Li) detetctors. From the observation of a linear relation between magnetic hyperfine fields at Gd and Tb nuclei in corresponding compounds, it is inferred that crystalfield induced variations of the Tb moment are negligible. The experimental results are discussed in terms of the conduction electron polarization caused by the magnetic moment of 3d metals.     

Exchange interaction effect of TbCo/FePt bilayers

Interlayer exchange coupling in dc-magnetron sputtered Tb_29.6Co_70.4/FePt bilayers with different annealing temperatures of the FePt film have been investigated. The dependence of ordering degree on perpendicular magnetic properties of the FePt film was studied. The Tb_29.6Co_70.4/FePt film has high perpendicular coercivity and high saturated magnetization about 7.5 kOe, and 302 emu/cm³, respectively as the substrate temperature is 500 °C and annealing at 500 °C for 30 min. It also shows a strong exchange coupling between this FePt layer and Tb_29.6Co_70.4 layer. We also examined the interface wall energy in the exchange coupled Tb_29.6Co_70.4/FePt double layers.     

First-order superconducting phase transition in CeCoIn5

The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K in zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c). The change from second order at lower fields is reflected in strong sharpening of both specific heat and thermal expansion anomalies associated with the phase transition, a strong magnetocaloric effect, and a steplike change in the sample volume. This effect is due to Pauli limiting in a type-II superconductor, and was predicted theoretically in the mid-1960s.     

非晶TbCo/Si多层膜的磁性和磁光特性

利用射频磁控溅射方法制备了非晶TbCo/Si多层膜,并对多层膜的磁性和磁光特性进行了测量.实验发现,随着Si层厚度的增加,非晶TbCo/Si多层膜的饱和磁化强度M_s、垂直各向异性常数K_u、磁光克尔角θ_K都显著下降.分析认为这是由于在TbCo层与Si层之间的层间互扩散形成了非磁性的Co₂Si所致. 关键词：     

Magnetic anisotropy in 5d transition metal–porphyrin molecules

Single molecule magnets(SMMs) with large magnetic anisotropy energy(MAE) have great potential applications in magnetic recording.Using the first-principles calculations,we investigate the MAE of 5 d transition metal-porphyrin-based SMMs by using the PBE and PBE+U with different U values,respectively.The results indicate that W-P,Re-P,Os-P,and Ir-P possess the considerably large MAE among 5 d TM-P SMMs.Furthermore,the MAE of 5 d TM-P can be facilely manipulated by tensile strain.The reduction of the absolute value of MAE for Ir-P molecule caused by tensile strain makes it easier to implement the writing operation.The decreasing of the occupation number of minority-spin channels of Ir-d_(x~2-y~2) orbital leads the MAE to decrease when the tensile strain increases.     

Topological quantum phase transition in 5d transition metal oxide Na2IrO3

We predict a quantum phase transition from normal to topological insulators in the 5d transition metal oxide Na2IrO3, where the transition can be driven by the change of the long-range hopping and trigonal crystal field terms. From the first-principles-derived tight-binding Hamiltonian, we determine the phase boundary through the parity analysis. In addition, our first-principles calculations for Na2IrO3 model structures show that the interlayer distance can be an important parameter for the existence of a three-dimensional strong topological insulator phase. Na2IrO3 is suggested to be a candidate material which can have both a nontrivial topology of bands and strong electron correlations.     

Phase transition in Pb5Al3F19

A study of the PbF₂-AlF₃ system has resulted in a new material Pb₅Al₃F₁₉ with a tetragonal structure at room temperature closely related to that of Pb₅Cr₃F₁₉. A phase transition in Pb₅Al₃F₁₉ has been detected by means of X-ray diffraction, calorimetric and dielectric measurements. The coexistence of the high and low-temperature Pb₅Al₃F₁₉ phases over the range 270 to 300 K and the abrupt 0.7% increase in the a-axis and 1.5% decrease in the c-axis, on heating through the phase transition, are characteristic of a first-order phase change. The increase in symmetry from point group 4 below to point group 4/m above the phase transition is consistent with a ferroelectric to paraelectric transition, as found previously in Pb₅Cr₃F₁₉.     

5d→4f transition in halosulphate phosphors

The synthesis, X-ray diffraction and photoluminescence characteristics in alkaline halosulphate phosphors, such as KZnSO₄Cl:Ce; KMgSO₄Cl:Ce; NaMgSO₄F:Ce and Na₃SO₄F:Ce is reported in this paper. The Ce³⁺ emission in KMgSO₄Cl:Ce phosphor is maximum and it may be useful for scintillation applications.     

Magnetic transition in ThCo5 due to change of Co-moment

ThCo₅ is ferromagnetic, the Co moment on the 3g-site (0.9 μ_B) is lower than that on the 2c-site (1.2 μ_B). In high fields, or in alloys slightly richer in Co, a structure of equal moments (1.50 μ_B) is observed. Above a critical value of the magnetic interactions, a metamagnetism of the 3d-band appears on the 3g-site.     

5d过渡金属氧化物中的奇异量子物性研究

相比于3d和4d过渡金属元素, 5d过渡金属元素既具有很强的自旋轨道耦合相互作用, 同时它们的电子关联作用也不可忽略. 因而5d过渡金属氧化物体系具有许多奇异的量子特性. 这篇综述主要介绍我们在5d过渡金属氧化物中的一些理论进展. 首先介绍烧绿石结构铱氧化物(A₂Ir₂O₇, A=Y或稀土元素)中的Weyl拓扑半金属性. 我们确定出A₂Ir₂O₇这一类具有阻挫结构材料的磁基态, 并预言其是Weyl半金属; 其Weyl 点受到拓扑保护而稳定, 而且它的表面态在费米能级形成特别的费米弧. 其次预言尖晶石结构锇氧化物(AOs₂O₄, A=Ca, Sr)是具有奇异磁电响应的Axion绝缘体; 然后分析了电子关联、自旋轨道耦合对钙钛矿结构的锇氧化物(NaOsO₃)的影响, 并成功定出它的基态磁构型, 最终确定其为Slater绝缘体. 最后介绍了LiOsO₃中铁电金属性的成因.     

The antiferromagnetic/paramagnetic transition in mixed-spin compounds R2BaNiO5

We present an extensive Quantum Monte Carlo study of the magnetic properties of the mixed-spin quantum systems R2BaNiO5 (R= magnetic rare earth) which show coexistence of 3-dimensional magnetic long-range order with 1-dimensional quantum gap excitations. We discuss the validity of the performed simulations in the critical region and show the excellent agreement with experimental results. We emphasize the importance of quantum fluctuations contained in our study which is absent in previous mean-field-like treatments.     

液Zn对Fe_2Al_5涂层侵蚀的相变过程研究

本文对Fe2Al5涂层在液态Zn中的侵蚀相变过程进行了研究,实验结果表明:在侵蚀初期,靠界面张力平衡的作用,先发生热侵蚀,在试样表面形成热蚀沟,当热蚀沟达到一定程度后,液Zn与Fe2Al5相由不浸润变为浸润;同时Zn原子扩散进入Fe2Al5相并形成Fe2Al5-Znx固溶体相(η相);随着侵蚀时间的增加,发生在腐蚀界面上的液Zn对Fe2Al5涂层的侵蚀过程是恒温相变过程,相变过程使Fe2Al5涂层发生定向熔化.相变的驱动力来自于相成分的改变所引起的各相自由能的变化及各相间的相平衡的重新建立.     

Insulator-metal transition in V3O5

The results of a study of the insulator-metal phase transition in V₃O₅ occuring at T = 450 K are presented. Conductivity, thermopower, magnetic, structural and optical data are reported. On a basis of the data obtained we conclude that the high-temperature phase is a poor metal with strong electron correlations and localized magnetic moments. The metal-non-metal transition is presumably driven by the spatial ordering of V³⁺ and V⁴⁺ ions.