Electronic structure and magnetic properties of Y4Co3

The electronic structure of Y₄Co₃ has been studied based on the density functional theory within the local-density approximation. The calculation indicates that Y₄Co₃ is very close to ferromagnetic instability. The Fermi surfaces are composed mainly of 3d electrons of Co and 4d electrons of Y.     

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 low field magnetisation of Y4Co3

The onset of magnetic order at 6 K and a superconducting transition at 2 K was previously observed in Y₄Co₃. In this paper we investigate the magnetisation in very low fields, in the vicinity of the magnetic and superconducting transition (T_c). Below T_c the M-H curves are characterised by broad hysteresis loops. This type of the behaviour indicates that the sample consists of different regions. Some of these regions are superconducting below T_c and others are magnetically ordered below 6 K.     

Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Tb₆Co_1.67Si₃ have been investigated by magnetization measurement. This compound is of a hexagonal Ce$_{6}$Ni$_{2}$Si$_{3}$-type structure with a saturation magnetization of 187\,emu/g at 5\,K and a reversible second-order magnetic transition at Curie temperature $T_{\rm C} = 186$\,K. A magnetic entropy change $\Delta S = 7$\,J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$ is observed for a magnetic field change from 0 to 5\,T. A large value of refrigerant capacity (RC) is found to be 330\,J/kg for fields ranging from 0 to 5\,T. The large RC, the reversible magnetization around $T_{\rm C}$ and the easy fabrication make the Tb₆Co_1.67Si₃ compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.     

Electronic structure and magnetic properties of Gd3Co11B4 compound

The electronic structure of hexagonal Gd₃Co₁₁B₄ compound has been studied by X-ray photoemission spectroscopy (XPS) and ab initio self-consistent tight binding linear muffin tin orbital (TB LMTO) method. We have found a good agreement between the experimental XPS valence band spectra and theoretical LMTO calculations. Results showed that the Gd₃Co₁₁B₄ compound is ferrimagnetic with the calculated total magnetic moment M=14.29 μ_B/f.u. The values of the magnetic moments on Co atoms strongly depend on the local environment. We have also compared the electronic structure and magnetic properties of Gd₃Co₁₁B₄ compound with those of Nd₃Co₁₁B₄ compound.     

Coexistence of magnetic and ferroelectric properties in Y0.1Co1.9MnO4

The magnetic,conductivity,and dielectric properties have been investigated in single-phase polycrystalline Y0.1 Co1.9 MnO4.The temperature-dependent magnetisation reveals the ferromagnetic transition in sample at a low temperature (～186 K).Magnetisation as a function of field H (M-H loop) indicated the weak ferromagnetism of the sample at room temperature.The constant ε and dielectric loss tgδ measurements represent a ferroelectric phase transition at a higher temperature (～650 K),while the conductivity shows an insulator-metallic transition.The ferroelectric hysterisis loops and capacitance-voltage measurements confirm the ferroelectric nature of the sample at room temperature.The observed ferromagnetism and ferroelectric nature in this material suggests a potential multiferroic application.     

Magnetic and transport properties of single-crystal Yb3Cu4Ge4

The magnetic and transport properties of single-crystal Yb₃Cu₄Ge₄ with the Gd₃Cu₄Ge₄-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8_μB/Yb$2.8{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5_μB/Yb$1.5{\mu }_{\mathrm{B}}/\mathrm{Yb}$ and 0.39_μB/Yb$0.39{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type$\lambda \mathrm{-}\mathrm{type}$ sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K² by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to T_C is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb₃Cu₄Ge₄ is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis.     

Magnetic properties of layer compound CsVF4

Magnetic properties of CsVF₄ have been studied by means of thermal diffusivity and neutron diffraction. The antiferromagnetic transition appearing at about 43 K is found to be of Ising spin order of V³⁺ magnetic moments which are oriented along the c-axis having the order of G-type. By applying a magnetic field vertically to the c-plane, it is also found that the magnetic moments of V³⁺ are re-oriented so as to be anti-parallel in each two-dimensional sheet of VF₆ octahedra and parallel between the network with the result that a ferromagnetic component appears.     

Magnetic Properties and magnetic phase diagrams of intermetallic compound GdMn2Ge2

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.     

Magnetic properties for the Mn2GeTe4 compound

Measurements of magnetic susceptibility χ, in the temperature range from 2 to 300 K, and of magnetization M vs. applied magnetic field B, up to 5 T, at various temperatures were made on polycrystalline samples of the Mn₂GeTe₄ compound. It was found that Mn₂GeTe₄ has a Néel temperature T_N of about 135 K, shows mainly antiferromagnetic behavior with a very weak superimposed ferromagnetic component that is attributed to spin canting. Also, the magnetic results suggest that a possible spin-glass transition takes place at T_f≈45 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory. The M vs. B results indicated that bound magnetic polarons (BMPs) occur in the compound, and that the effects from BMPs disappear at approximately 80 K. The M vs. B curves were well fitted by a Langevin type of equation, and the variation of the fitting parameters determined as a function of temperature. Using a simple spherical model, the radius of the BMP in the material was found to be about 27 Å; this value is similar to the effective Bohr radius for an acceptor in the II-IV-V₂ and I-III-VI₂ ternary semiconductor compounds.     

High field magnetization of Y2Co7 and YCo3 hydrides

The magnetization curves for the Y₂Co₇H_x and the YCo₃H_x systems have been measured at 4.2 K in the pulsed high magnetic fields up to 280 kOe. The metamagnetic transition is observed in the β and the γ hydrides except for Y₂Co₇H₃ and YCo₃H₁, which is interpreted in terms of the itinerant electron metamagnetism.     

Field dependence of the superconducting transition and of the onset of magnetism in Y4Co3

Measurements of a.c.-susceptibility in the temperature range from 0.1–12 K superimposed over d.c.-magnetic fields up to 1 T are reported. The results in zero d.c.-field have revealed the onset of magnetic order at 5.6 K and indicated a superconducting transition at 2 K. This transition was determined from the center of susceptibility decrease, in agreement with the result published recently by Kolodziejczyk et al. The superconducting transition is suppressed by an applied field of about 1 T. Down to the lowest obtainable temperature no reappearance of magnetic order has been found even in the highest applied field.     

The spin-glass state in Y2Co2/3Mo4/3O7 and Y2Fe2/3Mo4/3O7 complex oxides

The magnetic properties of Y₂ B _2/3Mo_4/3O₇ complex oxides (B = Co, Fe) were studied in the temperature range 2–300 K. At low temperatures, these compounds exhibit spin-glass properties with freezing temperatures T _f=26 and 33 K, respectively, and typical features in the magnetic hysteresis and in the dependences of the real part of the dynamic magnetic susceptibility on temperature and ac magnetic field frequency. Above T _f, the static magnetic susceptibility of the samples studied depends on the applied magnetic field, which is tentatively assigned to the presence of metallic cobalt and/or yttrium orthoferrite YFeO₃ introduced in the course of sample preparation. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 12, 2005, pp. 2182–2188. Original Russian Text Copyright ? 2005 by Bazuev, Korolev.     

Magnetic properties of PuNi3 type intermetallic compounds YxZr1−xCo2.9 and their hydrides

Magnetization and Curie temperature of Y_xZr_1−xCo_2.9 decrease with decreasing x. Their hydrides with x0.8 are paramagnetic with an anomaly and those of 0.7x0.5 become weak ferromagnets. The spin structure is discussed.     

Magnetoelastic properties of ErMn6Sn6 intermetallic compound

The thermal expansion and magnetostriction of polycrystalline sample of the ErMn₆Sn₆ intermetallic compound with hexagonal HfFe₆Ge₆-type structure are investigated in the temperature range of 77 K to above 400 K. The thermal expansion measurement of the sample shows anomalous behavior around its T_N=340 K. The isofield curves of volume magnetostriction also reveal anomalies at paramagnetic-antiferromagnetic and antiferromagnetic-ferrimagnetic phase transitions. In the antiferromagnetic state, the transition to ferrimagnetism can be induced by an applied magnetic field. The threshold field for the metamagnetic transition H_th increases from 0.18 T at 84 K to about 1 T around 220 K, and then decreases monotonously to T_N. This behavior is well consistent with that observed earlier on magnetization curves attributed to exchange-related metamagnetic transition rather than the anisotropy-related one. Furthermore, the low H_th values suggest that the Mn-Mn coupling in ErMn₆Sn₆ is not so strong. The experimental results obtained are discussed in the framework of two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for this compound.     

Magnetoelastic properties of GdMn6Sn6 intermetallic compound

We studied the thermal expansion and magnetostriction of polycrystalline samples of GdMn₆Sn₆ intermetallic compound with hexagonal HfGe₆Fe₆-type structure in the temperature range of 77-520 K. The thermal expansion measurement of the sample shows anomalous behavior around its T_C=434 K and T_M=309 K, possibly the point of collapse-like reduction of Mn moments. In addition, the isofield curves of anisotropic and volume magnetostriction reveal anomalies around paramagnetic to ferrimagnetic phase transition. The obtained experimental results are discussed in the framework of two-magnetic sublattices by bearing in mind the lattice parameter dependence of interlayer Mn-Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants as well as a comparison of their orders of magnitude for this compound.     

Magnetic and electronic properties of the antiferromagnetic YbFe4Al8 compound

The magnetic, electrical and electronic properties of the tetragonal ternary YbFe₄Al₈ compound have been investigated. This compound was supposed to be an antiferromagnetic superconductor due to the negative magnetization signal appearing at a low field of the field cooling mode, however, based on the measurements of the temperature dependence of magnetization and resistivity we do not confirm the presence of superconductivity in this material and we ascribe the negative magnetization to the complicated non-collinear magnetic structure. A switch to the antiferromagnetic order at about 150 K has been visible both on the M(T) and ρ(T) curves. The valence state of the Yb ions has been studied by X-ray photoemission spectroscopy. The valence band spectrum at the Fermi level exhibits the domination of the hybridized Yb(4f) and Fe(3d) states.     

Electrical properties of the intermetallic compound Mn3Sn

Temperature variations of resistivities are measured on the single crystals of Mn₃Sn with a hexagonal crystal structure. Anomalies of resistivity along the c-axis are observed at 230 and 420 K which correspond to the transition temperature from a tringle-helix to triangular spin structure state and the Néel temperature, respectively.     

混合自旋反铁磁材料Y2BaNiO5的磁学和热力学性质

在格林函数的理论框架下，采用一维自旋为1的各向异性Heisenberg模型来讨论Y₂BaNiO₅材料的磁学和热力学性质.得到了它的自旋关联函数、低激发谱、基态能(E_g)、比热(C)和静态磁化率(χ)在不同交换各向异性因子下的性质，所得结果与实验和数值模拟结果完全一致. 关键词： Heisenberg模型 格林函数理论 Haldane能隙 反铁磁长程序     

One-dimensional effects in the intermetallic compound Al11Mn4

Magnetic susceptibility and electrical resistivity measurements show that the intermetallic compound Al₁₁Mn₄ has a one-dimensional magnetic character. This is attributed to the presence of chains of nearest neighbour Mn atoms together with a strongly depressed interaction between distant Mn atoms.